The European athecate hydroids and their medusae (Hydrozoa, Cnidaria): Capitata Part 1

Abstract

This study reviews all European hydrozoan species belonging to the capitate families Acaulidae, Boreohydridae, Candelabridae, Cladocorynidae, Cladonematidae, Margelopsidae, Pennariidae, Protohydridae, and Tricyclusidae. Updated diagnoses for the families and genera are provided and existing taxonomic problems solved or at least outlined. Candelabrum verrucosum Bonnevie, 1898 is regarded as a valid species and redescribed based on a new record from Greenland. Although Spadix purpurea Gosse, 1853 may be a senior synonym of Candelabrum cocksii (Cocks, 1854), the latter is regarded as the valid name, this because the former name has not been used after 1899, while the latter has been widely used [ICZN article 23.9.1.1]. Likewise, two senior synonyms of Eleutheria claparedii Hartlaub, 1898 are declared as invalid as they have never been used since their original introduction by Haeckel.

Full text

The European athecate hydroids and their medusae
(Hydrozoa, Cnidaria): Capitata Part 1
Peter SCHUCHERT
Muséum d'histoire naturelle, CP 6434, CH-1211 Genève 6, Switzerland.
E-mail: Peter.Schuchert@ville-ge.ch
The European athecate hydroids and their medusae (Hydrozoa,
Cnidaria): Capitata Part 1. - This study reviews all European hydrozoan
species belonging to the capitate families Acaulidae, Boreohydridae, Can-
delabridae, Cladocorynidae, Cladonematidae, Margelopsidae, Pennariidae,
Protohydridae, and Tricyclusidae. Updated diagnoses for the families and
genera are provided and existing taxonomic problems solved or at least out-
lined. Candelabrum verrucosum Bonnevie, 1898 is regarded as a valid
species and redescribed based on a new record from Greenland. Although
Spadix purpurea Gosse, 1853 may be a senior synonym of Candelabrum
cocksii (Cocks, 1854), the latter is regarded as the valid name, this because
the former name has not been used after 1899, while the latter has been
widely used [ICZN article 23.9.1.1]. Likewise, two senior synonyms of
Eleutheria claparedii Hartlaub, 1898 are declared as invalid as they have
never been used since their original introduction by Haeckel.
Keywords: Marine invertebrates - Cnidaria - Hydrozoa - Anthoathecata -
Capitata - descriptions - revision - taxonomy.
INTRODUCTION
This publication is the second in a series of taxonomic revisions of the
European Anthoathecata (=Anthomedusae, Athecata) which was begun with the
families Oceanidae and Pachycordylidae (Schuchert, 2004). Although it was initially
planned to continue with families of the suborder Filifera, some essential material
could not be obtained to complete them in time. Therefore, this second paper presents
some families of the suborder Capitata.
Following the suggestions of fellow colleagues, the geographic scope of the
fauna under investigation has been somewhat extended to match the territory covered
by the European Register of Marine Species (Costello et al.,2001). The new scope
now also includes the Azores, Iceland, eastern Greenland, Jan Mayen, the Barents Sea,
Svalbard, and Franz Joseph Land. The extension of the geographic scope does not add
many species. A single species needs to be added to the families treated in the first
paper of this series, namely Similomerona nematophora (Antsulevich, 1986). This
species is already mentioned and diagnosed in Schuchert (2004), but its type locality
was erroneously given as "Kurile Islands". Dr Antsulevich informed me that the
REVUE SUISSE DE ZOOLOGIE 113 (2): 325-410; juin 2006
Manuscript accepted 19.10.2005

species was described from material originating from the archipelago of Franz Joseph
Land, thus falling within the limits of the newly adopted coverage. Furthermore,
although the paper was authored by Antsulevich & Polteva (1986), the authorship of
the species name is due to Dr Antsulevich alone. Although the genus name Merona is
an artificial word, its ending is characteristic for the feminine gender, thus requiring a
change of the specific epithet to nematophora.
The current paper treats several families of the suborder Capitata. The families
reviewed here were chosen somewhat arbitrarily and do not form a natural unit, though
some are evidently closely related. The selection had to be based on the material
available for study. The order of the families as given below has no phylogenetic
significance and is only thought to group somewhat similar forms together. For a
phylogenetic analysis of these families see Petersen (1990). Molecular phylogenies of
some families of Capitata can be found in Collins et al. (2005a, and b).
MATERIAL AND METHODS
For morphological methods see Schuchert (1996; 2004) or Bouillon et al.
(2004). Where possible, it was attempted to supplement the species descriptions by 16S
DNA sequence information. The methods to obtain 16S DNAsequences are described
in Schuchert (2005). All sequences have been submitted to the EMBL database under
the accession numbers: AM088481, AM088482, AM088483, AM088484, AM088485.
The origin and identity of the material used to obtain 16S sequence data are given for
each species in the section "Material examined". Some sequences have been deter-
mined by other laboratories using material described here (accession numbers
AY920796, 18S AY920758, AY787879, AY920762, AY512539). Morphological
characters of the Cladonematidae were used for a phylogenetic analysis using the
parsimony criterion and the program PAUP* (Swofford, 2001). Bootstrap replicates
were performed 1000 times. Only a subset of all Cladonematidae was used. The
members of the genus Cladonema are all very similar and well represented by C. ra-
diatum.For Staurocladia,only those species with known life cycle were used. As out-
group taxa, three members of the Corynidae were used (comp. Schuchert, 2001b).
Table 1 gives the species names and the characters used and their states.
ABBREVIATIONS
BMNH The Natural History Museum, London, England
MHNG Muséum d’histoire naturelle de Genève, Switzerland
ICZN International Code of Zoological Nomenclature
IRSN Institut Royal des Sciences Naturelles de Belgique, Bruxelles
ZMUC Zoological Museum Copenhagen, Denmark
CI Consistency index
RI Retention Index
HI Homoplasy Index
TAXONOMIC PART
FAMILYACAULIDAE FRASER, 1924
DIAGNOSIS:Solitary hydroids, body divided into basal and distal part. Basal part
conical to cylindrical, covered or not by gelatinous perisarc which may form anchoring
P.SCHUCHERT
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filaments. Upper part with few indistinctly capitate tentacles or many capitate
tentacles, lowest whorl of capitate tentacles may transform into thick filiform tentacles.
Gonophores fixed sporosacs in the lower or middle part of the hydranth. Sometimes
asexual reproduction by transverse fission.
REMARKS:The name Acaulidae was proposed by Fraser (1924) and this spelling
was used by all subsequent authors. According to the ICZN [article 29.3.1.1] there is
thus no need to change it to the formally correct Acaulididae.
According to Bouillon (1985), this family contains two genera: Acaulis
Stimpson, 1854 and Acauloides Bouillon, 1965. Petersen (1990) also included the
genus Boreohydra Westblad, 1937 in the Acaulidae, while Bouillon (1985) kept
Boreohydra in a separate family Boreohydridae, this together with the genus Proto-
hydra.A third genus was later added to the Acaulidae by Thomas et al. (1995):
Cryptohydra. The discovery of Cryptohydra narrowed the gap of the Acaulidae to the
genus Protohydra – and thus Boreohydridae – to a degree that any subdivision now
appears entirely arbitrary. The proximity of both families is further emphasized if the
nematocyst warts on the body of Boreohydra are regarded as reduced capitate tentacles
(Calder, 1974). It is thus tempting to fuse both families, but this should only happen in
the framework of a broader analysis and discussion and the phylogenetic relationships.
The Acaulidae and Boreohydridae have also many similarities with the Candelabridae
and Tricyclusidae, and the demarcations are equally arbitrary.Because a phylogenetic
analysis based on morphological characters alone appears not so promising (see
Petersen, 1990), it is therefore preferable to wait with a revision until a thorough
molecular analysis provides the necessary robust phylogeny.Meanwhile, the classifi-
cation according to Bouillon (1985) is here used in order to maintain nomenclatural
stability.
Through monotypy,the genus Acauloides Bouillon, 1965 is unfortunately based
on Acauloides ammisatum, an insufficiently known species. Acauloides is thus essen-
tially distinguished from Acaulis through the absence of filiform tentacles. The filiform
tentacles of Acaulis are formed relatively late in development through the transfor-
mation of capitate tentacles (Berrill, 1952). Using this ontogenetic argument and also
outgroup comparisons to the Tricyclusidae and Candelabridae, it is evident that filiform
tentacles of Acaulis are apomorphic. The absence of filiform tentacles in the genus
Acauloides is thus a plesiomorphic trait and unsuitable to reveal a monophyletic group.
The genus Acauloides could nevertheless be valid, as in Acauloides ilonae the
gonophores develop in the upper axils of the tentacles, which is clearly an apomorphy
for this genus. Because Acauloides ilonae is perhaps a synonym of A. ammisatum,it is
thus recommendable to continue to use the genus Acauloides in order to maintain
nomenclatural stability.
KEY TO GENERA:
1a hydranth small, very elongated, all tentacles indistinctly capitate
.......................................Cryptohydra (not in European fauna)
1b majority of tentacles distinctly capitate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2a mature hydranth with a whorl of thick filiform tentacles . . . . . . . . . . . . . . . . . . . Acaulis
2b all tentacles capitate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acauloides
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

Genus Acaulis Stimpson, 1854
TYPE SPECIES:Acaulis primarius Stimpson, 1854.
SYNONYMS:Blastothela Verrill, 1878: 374; ? Myriocnida Stechow, 1909 (invalid nomen
nudum).
DIAGNOSIS:Hydroid connected to substrate by modified hydrocaulus secreting
agelatinous sheath or forming anchoring filaments; hydranth fusiform; capitate tenta-
cles in one oral whorl and more scattered below, solid, with chordoid gastrodermis; be-
low capitate tentacles one whorl of filiform, long, stout, aboral tentacles developing by
transformation of capitate tentacles; gonophores fixed, carried singly or in clusters on
short pedicels.
REMARKS:Stechow (1909) introduced the genus name Myriocnida for a hydroid
described in Fewkes (1890) as Acaulis (without specific epithet). Because it was not
based on a nominal species, the genus is not valid. It remains unclear to which species
Fewkes' material belonged (he described it from notes made by someone else). It could
have been be either Acaulis or more likely an incomplete Candelabrum species.
Acaulis primarius Stimpson, 1854 Fig. 1
Acaulis primarius Stimpson, 1854: 10, pl. 1 fig. 4; Allman, 1872: 378; Sars, 1874: 123, pl. 5 figs
14-20; Will, 1913: 57, pl. 26; Scheuring, 1922: 167, pl. 5 fig. 1; Berrill, 1952: 17, fig. 6;
Rees, 1957: 466, fig. 13; Bouillon, 1971: 342, pl. 4; ? Verwoort, 1985: 269, plate 1;
Schuchert, 2001a: 35, fig. 22A-D.
Acaulis primaris – Naumov, 1969: 243, fig. 112 [incorrect subsequent spelling].
MATERIAL EXAMINED:Material from Iceland and Greenland as given in Schuchert
(2001a).
DIAGNOSIS:Acaulidae with filiform tentacles in mature animals, sporosacs not
in axils of tentacles, base without attachment filaments.
DESCRIPTION:Solitary hydroids, body thickly fusiform to cylindrical, divided
into basal part (approx. 1/5 of height, variable) and upper part. Both parts separated by
one whorl of five to eight thick tapering tentacles covered evenly with nematocysts.
Basal part conical to cylindrical, surrounded by thick jelly covered by adhering
detritus. Upper part of hydranth roughly cylindrical with up to 50 scattered capitate
tentacles; hypostome rounded. Gonophores on lower part of region with capitate
tentacles but not associated with the tentacles. Gonophores sessile sporosacs with
spadix but without radial or ring canals. Nematocysts: stenoteles, microbasic
heteronemes (euryteles or mastigophores), and desmonemes.
DIMENSIONS:Mature polyps are 5 to 10 mm in height, extended up to 2 cm
(Westblad, 1947), gonophores ca. 0.5-0.6 mm. Nematocysts: stenoteles, (18-21)x(14-
17) mm; heteronemes, (16-20)x(7-10.5) mm; desmonemes, (12-15.5)x(8.5-10.5) mm.
DEVELOPMENT:Young hydranths have no filiform tentacles, only capitate ones.
During growth, the lowest capitate tentacles become elongated and thicker, and the
nematocyte free regions of the tentacles are subsequently covered by nematocytes (see
Fig. 1A-B) (Berrill, 1952). The development of the gonophores can begin before the
filiform tentacles have completed their transformation.
P.SCHUCHERT
328

ADDITIONAL DATA:Westblad (1947) describes and depicts both the gonophore
development and gametogenesis. Westblad (1947) also depicts the nematocysts and de-
scribes their distribution.
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG.1
Acaulis primarius Stimpson, 1854; after Schuchert (2001a), Icelandic material. A) Juvenile,
scale bar 0.5 mm, also valid for sections B-C. B) Intermediate sized specimen with beginning
transformation of lowest tentacles. C) Mature female, filiform tentacles fully developed. D)
Nematocysts, as seen in preserved material: stenotele, microbasic heteroneme, desmoneme,
scale bar 10 µm.

BIOLOGY:Acaulis primarius lives usually partially embedded in sediment
bottoms at depths of down to 350 m, usually not above 20 m depth (Berrill, 1952;
Schuchert, 2001a).
DISTRIBUTION:Northern Atlantic, Arctic to boreal regions; New England, New
Brunswick, north-west coast of Norway, Barents Sea, White Sea (Scheuring, 1922;
Fraser, 1944; Naumov, 1969), North Sea, Sweden (Jäderholm, 1909; Westblad, 1937;
Bouillon et al.,1995), Baltic Sea (Will, 1913; Schönborn et al.,1993), Iceland
(Schuchert, 2001a), western Greenland (Schuchert, 2001a). Perhaps also Bay of Biscay
(Vervoort, 1985, identification uncertain). Type locality: Grand Manan, Bay of Fundy,
Canada.
REMARKS:Stimpson (1854) described Acaulis primarius based on two sets of
animals collected at different times. The first animal he found and depicted corres-
ponds exactly to our current concept of Acaulis primarius.The second set he found
later, attached to red-algae (it is unclear in what depth, he states 5-15 f., which could
be feet or fathoms, both interpretations can be found in the literature, but the latter
being more probable). In the second set of specimens the tentacles were much longer,
the hydranths resembled a corynid and they reportedly produced medusae. Allman
(1872), Will (1913), and Fraser (1924) noticed this difference and assumed that the
second set of Stimpson’s material belonged to another species than Acaulis primarius.
Allman (1872) restricted the scope of Acaulis to the animal depicted in Stimpson
(1854), thus he de facto selected a lectotype and Acaulis primarius is thus well defined.
Genus Acauloides Bouillon, 1965
TYPE SPECIES:Acauloides ammisatum Bouillon, 1965, by monotypy.
SYNONYMS: ? Psammocoryne Monniot, 1962 (invalid nomen nudum).
DIAGNOSIS:Hydroid attached to substrate by modified hydrocaulus, secreting a
gelatinous sheath or mucous film; capitate tentacles in one oral whorl and more
scattered below,solid, with chordoid gastrodermis; without filiform tentacles;
gonophores in upper axils of tentacles, asexual reproduction through transverse fission.
Acauloides ammisatum Bouillon, 1965 Fig. 2
?Psammocoryne. – Monniot, 1962: 274, fig. 14b [nomen nudum].
Acauloides ammisatum Bouillon, 1965: 54; Bouillon, 1971: 335, figs IV8-11, V-VI; Bouillon
et al.,2004: 86, fig. 47H.
MATERIAL EXAMINED:None, type material could not be located.
DIAGNOSIS:Acaulidae with capitate tentacles only, adults 0.6-2 mm, 10-25
tentacles, peduncle without gelatinous tube, only mucous secretion at its end for
attachment to sand grains.
DESCRIPTION:Solitary hydroids, thick fusiform shape, short peduncle of about
1/3 of total height, peduncle without gelatinous tube but at end mucous secretion by
which the animal attaches itself to sand grains. Tentacles all capitate, 10-25, one oral
whorl of 4-6 short tentacles, remaining scattered below on body, those in middle of
body longest, others very short to almost lacking a stalk. Nematocysts: stenoteles;
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desmonemes; holotrichous microbasic mastigophores, when discharged shaft longer
than capsule. Vegetative and sexual reproduction not known.
DIMENSIONS:Polyps 0.6-2 mm. Nematocysts: stenoteles 17x14 µm, desmo-
nemes 6x10 µm, microbasic mastigophores (16-18)x(6-8)µm.
ADDITIONAL DATA:Bouillon (1971) provides further details on the histology and
cytology of this species.
DISTRIBUTION:Roscoff, Brittany; ? Banyuls-sur-Mer (Mediterranean). Type
locality: Roscoff, English Channel.
REMARKS:Acauloides ammisatum Bouillon, 1965 strongly resembles the vege-
tative reproduction stage of A. ilonae (Brinckmann-Voss, 1966) and the two are
possibly conspecific. There are some minor size differences, with A. ammisatum being
smaller and having slightly larger nematocysts. Another formal difference is the
absence of a gelatinous tube in A. ammisatum, for which only a mucous cover has been
described. However,such a mucus cover might be only the initial stage of a gelatinous
tube, a type of cover which is only seen in fully grown animals. There is also a possible
ecological difference: while A. ammisatum occurs on sand, A. ilonae has been found
on mud only.More data – especially on mature animals from Roscoff – are needed
before a final more definite conclusion is possible. Meanwhile, both nominal species
should be kept separate.
Bouillon (1971) also attributed to this species some animals from Banyuls
(Mediterranean) depicted in Monniot (1962). Monniot found her animal in coarse sand
and identified it as Psammocoryne. This name is not a valid genus as it was not asso-
331
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 2
Acauloides ammisatum Bouillon, 1965; modified after Bouillon (1971), no scale given. A)
Polyp. B) Stenotele, larger mastigophore, smaller mastigophore, discharged mastigophore.

ciated with a valid nominal species. Furthermore, Monniot's hydroid could easily also
be referred to A. ilonae and it is therefore also somewhat unclear whether A. ammisa-
tum also occurs in the Mediterranean (this in case that they are not conspecific).
Acauloides ilonae (Brinckmann-Voss, 1966) Fig. 3
Acaulis ilonae Brinckmann-Voss, 1966: 292, figs 1-10; Brinckmann-Voss, 1970: 44, text-fig. 51,
pl. 1 figs 4-6.
Acauloides ilonae –Bouillon et al., 2004: 86, fig. 47I.
MATERIAL EXAMINED:Syntypes (labelled holotype), BMNH 1963.12.9.1, as Acaulis ilon-
ae,two specimens, both broken. – BMNH 1974.11.21, as Acaulis ilonae,Naples, 20.10.1960-
29.11.1961, leg. Brinckmann-Voss, one female, pedicel broken off.
DIAGNOSIS:Acaulidae with capitate tentacles only, sexually reproducing adults
5-10 mm, about 2 mm in phase of vegetative reproduction; sporosacs in upper axils of
tentacles, peduncle of adult hydranths in gelatinous sheath.
DESCRIPTION (after Brinckmann-Voss, 1966; 1970; and own observations):
Mature hydroid spindle shaped, divided into two parts of roughly the same length: an
upper tentacle-bearing part and a basal part without tentacles called peduncle (or
"foot"). Peduncle tapering, surrounded by a gelatinous sheath which adheres to mud
particles or cultivation vessels, gastrodermis highly vacuolated. Tentacles all capitate,
solid, up to 60, one oral whorl of four to five tentacles and a basal whorl comprising
the same number of tentacles, between them a number of scattered tentacles, often in
groups of two to three around a sporosac, tentacle length unequal, longest ones more
proximal, diameter of capitula also variable. Gonophores are sporosacs without radial
canals, developing always in upper axils of tentacles in middle region of tentaculate
part, oldest sporosacs in middle, younger ones proximal and distal to them. New ten-
tacles often formed close to the gonophores. Colour of the animals pink to orange, with
anumber of white dots on surface, very old specimens have a brownish colour,nema-
tocysts: stenoteles, microbasic euryteles and desmonemes. Fertilized eggs developing
acapsule and going through an encysted resting stage.
Polyps in vegetative phase of reproduction small, with 29-35 tentacles, attached
to substratum, multiplying by binary fission in region of tentacles.
DIMENSIONS:Sexually reproducing animals up to 10 mm, polyps in phase of
vegetative multiplication up to 2 mm. Diameter of eggs 0.15 mm. Nematocysts:
desmonemes (8.4-12.6)x(7.6-9.2)µm; stenoteles (18.5-22.7)x(16.0-19.3)µm; microba-
sic euryteles (11.8-14.3)x(3.4-7.6)µm (Brinckmann-Voss, 1966).
DISTRIBUTION:Naples, questionably also Roscoff, Brittany, although the latter
records may refer to A. ammisatum.Type locality: Gulf of Pozzuoli, Naples, Italy, 45 m.
BIOLOGY (after Brinckmann-Voss, 1966; 1970): Acauloides ilonae is able to
creep sluggishly on the substrate. The animals are gonochoristic; female and male hy-
droids continue to spawn their gametes several times for more than a year,the gametes
differentiate continuously. Eggs are usually shed during the night and early morning
hours, fertilisation takes place in the seawater. The embryo does not swim and attaches
itself to the ground and transforms into a flattened body which is covered with thin,
transparent cuticula. The cyst remains attached for at least one month, after which a
P.SCHUCHERT
332

small polyp without tentacles hatches very slowly (it takes 2-3 days). Hydroids hatch
from cysts only if kept in water of 13°C, at 20°C the hatching rate is poor. The young
polyp grows to a size of about 2 mm and then starts the vegetative reproduction phase
by transverse fission. At 20°Cdivisions take place every 10-45 days and if kept at 20°
the fission continues, the polyps do not exceed 2-3 mm, and they do not develop
gonophores. Polyps that had undergone divisions and are brought to 13° do not divide
anymore, they begin to grow in length, get more tentacles and develop gonophores in
the axils of the tentacles, thus starting the sexual phase. Individuals that had hatched
from cysts and are cultured at 13° undergo one or two rounds of divisions before they
develop gonophores. Sexual maturity is not reached without having first undergone
asexual division.
The hydroid was found on surface of mud in depths of 20 to 80 m. It occurred
in abundance around Naples from November to April. It was not found from July to
October. It is thus a winter species.
REMARKS:Brinckmann-Voss (1966) described her material based on animals
from Naples, but also mentioned that Bertil Swedmark had found it at Roscoff too (via
personal communication by J. Rees). Because it appears that the latter material was
333
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 3
Acauloides ilonae (Brinckmann-Voss, 1966), modified after Brinckmann-Voss (1966), scale bar
1mm. A) Sexually reproducing polyp. B) Vegetatively reproducing polyp just after fission, with
aboral and oral parts.

more likely Acauloides ammisatum (see remarks in Bouillon, 1971: 335), the occur-
rence of A. ilonae outside the Mediterranean is uncertain (if the two indeed prove to be
distinct species, see remarks under A. ammisatum).
FAMILY BOREOHYDRIDAE WESTBLAD, 1947
TYPE GENUS:Boreohydra Westblad, 1937.
DIAGNOSIS:Hydroids solitary, small, with one whorl of reduced tentacles,
capitate or not, located in the oral or median part of body; perisarc covering of base
filmy or absent; gametes in body wall.
REMARKS:Representing likely a simplified form, the affinities of the genus
Boreohydra with its sole species B. simplex remains controversial. Westblad (1947)
considered it related to the Tubulariidae, but sufficiently distinct to deserve being
placed in a separate family.Rees (1957) could not agree and placed it in the
Corymorphidae. Calder (1974) thought that if the nematocyst clusters on the body
should prove to be nothing but reduced capitate tentacles, then the genus should belong
to the Candelabridae. Bouillon (1985) considered the family Boreohydridae as valid
and added also the genus Psammohydra to it, this because of the resemblance of their
cnidome. Petersen (1990) placed Boreohydra among the Acaulidae, but gives no
arguments for this and he does not discuss Psammohydra.As already stated for the
family Acaulidae, the problem is not resolvable by traditional approaches and, pending
amolecular analysis, the family Boreohydridae is here retained for the time being.
KEY TO THE GENERA:
1a hydranth with oral capitate tentacles and nematocyst buttons on body . . . . . Boreohydra
1b filiform tentacles in middle of body; hypostome proboscis-like . . . . . . . . Psammohydra
Genus Boreohydra Westblad, 1937
TYPE SPECIES:Boreohydra simplex Westblad, 1937.
DIAGNOSIS:Solitary hydroids of small size, living buried in the sediment; caulus
covered by filmy perisarc; one whorl of capitate tentacles near mouth and numerous
scattered nematocyst clusters on hydranth body. Gametes in epidermis at junction of
hydranth body and caulus; asexual reproduction by transverse fission.
REMARKS:This is currently a monotypic genus.
Boreohydra simplex Westblad, 1937 Fig. 4
Boreohydra simplex Westblad, 1937: 1, figs 1-4; Westblad, 1947: 1-13, figs 1-4, pls 1-3; Nyholm,
1951b: 531, text fig., pl. 1 figs 1-4; Westblad, 1953: 351, figs 1-2; Prévot, 1959: 97,
pl. 1 fig. 2; Calder, 1974: 1666, fig. 1; Bozhenova et al.,1989: 11, fig.; Petersen, 1990:
148; Schuchert, 2001a: 36, fig. 23A-B; Bouillon et al.,2004: 86, fig. 47L.
MATERIAL EXAMINED:See Schuchert (2001a).
DIAGNOSIS:Small, solitary,mud-dwelling hydroids with three to four capitate
oral tentacles and scattered wart-like nematocyst clusters on hydranth body.
DESCRIPTION:Solitary hydroid, composed of hydranth body and conical
peduncle. Hydranth spindle-shaped, hypostome short and rounded, surrounded by
P.SCHUCHERT
334

three to four short, stubby tentacles, only slightly capitate. On hydranth body 50-60
scattered nematocyst clusters, variable in size, 3-15 capsules per cluster, clusters slight-
ly elevated and wart-like. Hydranth body at base tapering and turning into peduncle,
peduncle conical, constantly tapering into fine tip at its end, covered by wrinkled
perisarc. Gastrodermis with three or four longitudinal folds. Nematocysts: stenoteles;
desmonemes, discharged with four coils; isorhizas.
DIMENSIONS: Hydranth body height 0.8-1.5 mm, diameter about 0.3 mm;
peduncle 0.4-1 mm long. Nematocysts: stenoteles (17-19)x(16)µm; desmonemes,
(16-17)x(9-11)µm; isorhizas (17-20)x(4.5-5.5)µm.
BIOLOGY:Fairly common in mud bottoms characterized by the 'Brissopsis
lyrifera - Amphiura chiajei'community (Petersen, 1913; Jones, 1950) at depths of
around 40 m (Westblad, 1953). The depth range varies from a few metres to more than
600 m (Christiansen, 1972). The animal is able to move quite rapidly on the surface of
mud (Hult, 1941). The latter author also described how it burrows into the mud. The
oral tentacles are instrumental for this process. The food seems to be mainly composed
of small nematodes (Westblad, 1947).
ADDITIONAL DATA: (Westblad, 1947; Nyholm, 1951b) The polyp multiplies by
transverse fission and produces gonophore-like outgrowths without germ-cells. Eggs
were found in the epidermis at the junction of the body and peduncle. Westblad (1947)
gives further details on the variability: of 60 animals, 47 had three tentacles, the others
four. The number of tentacles and the number of gastrodermal folds is not closely
correlated. Prévot (1959) depicts a longitudinal section. Bozhenova et al.,(1989)
depict the nematocysts and provide measurements.
335
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 4
Boreohydra simplex Westblad, 1937; Northern Greenland, Pearyland, after Schuchert (2001a).
A) polyp, scale bar 0.2 mm. B) stenotele, desmoneme, isorhiza, scale bar 10 µm

DISTRIBUTION:Bipolar, northern and southern Atlantic Ocean in temperate to
Arctic waters, probably quite frequent, but often overlooked. It was particularly often
recorded along the Atlantic coast of Scandinavia. The southern limit for Europe is the
English Channel. Recorded from the White Sea, Norway to Sweden, Great Britain,
Iceland, North Greenland, North-Eastern Canada, North Greenland, South Georgia
(Hult, 1941; Westblad, 1953; Christiansen, 1972; Calder, 1974; Bozhenova et al.,
1989; Schuchert, 2001a). Type locality: Tromsø and Ramfjord, Norway.
REMARKS:Westblad (1947) supplemented the first description by further
anatomical and ecological details. He observed buds that he interpreted as gonophores,
however he could not find germ cells in them. Later, Nyholm (1951) observed eggs in
the epidermis and concluded that the germ cells of this species are not collected in
sporosacs, but remain in the epidermis like in Hydra.Petersen (1990) interpreted the
gonophore-like outgrowths observed by Westblad (1947) as incipient polyp buds.
More work is needed to reveal the nature of these buds.
Genus Psammohydra Schulz, 1950b
TYPE SPECIES:Psammohydra nana Schulz, 1950b.
DIAGNOSIS:Solitary hydroids of very small size, living attached to sand grains;
one whorl of filiform tentacles in middle region of hydranth; hypostome proboscis-like,
with terminal swelling. Asexual reproduction through fission.
REMARKS:This is currently a monotypic genus. The sexual reproduction is in-
sufficiently known.
Psammohydra nanna Schulz, 1950 Fig. 5
Psammohydra nanna Schulz, 1950b: 122, figs 1-9; Riedl, 1970: 153, pl. 43; Clausen, 1971: 2,
fig. 1; Clausen & von Salvini-Plawen, 1986: 34, fig. 3; Thiel, 1988: 267, fig. 19.1d;
Bouillon etal.,2004: 87, fig. 48A.
MATERIAL EXAMINED:None, the type material could not be located.
DIAGNOSIS:Very small solitary hydroid living attached to sand grains, body skit-
tle- to spindle shaped, one whorl of filiform tentacles in about middle of body.
DESCRIPTION:Tiny solitary hydroids, living attached to sand-grains; body shape
and size very variable, usually skittle- or spindle-shaped, with flat base when attached,
slightly above middle a single whorl of four (rarely 3-5) tentacles; hydranth body
above tentacles proboscis-like, with terminal swelling. Proboscis movable and exten-
sible, mouth terminal but invisible when not used. Tentacles short, straight, contractile,
filiform, nematocysts evenly distributed, gastrodermis chordoid. Sexual reproduction
insufficiently known, reportedly only one egg is produced. Colour: sand-grey. Nemato-
cysts: stenoteles, desmonemes, atrichous isorhizas.
DIMENSIONS:Total body size 0.28-0.4 mm, but very variable, can contract or
expand its body about two times. Nematocysts: stenoteles (6-7)x(5-6)µm, isorhizas
(5.5-6.8)x(2.3-3)µm; desmonemes (3.5-5.5)x(2.3-3.5)µm(Schulz, 1950b).
BIOLOGY:Vegetative reproduction takes place by transverse fission. The animal
can move by creeping like a freshwater Hydra. It is a member of the meiofauna and
P.SCHUCHERT
336

occurs in fine sand in shallow waters of a few metres. Schulz (1950b) characterizes the
community where it was found as "Turbanella hyalina"community (Remane, 1933).
It can tolerate reduced salinity down to 8‰ (Schönborn et al., 1993).
ADDITIONAL DATA :Of 46 examined animals, 39 had four tentacles, four had
three tentacles, and three five (Schulz, 1950b). Schulz (1950b) also describes the
histology of this animal. The gastrodermal epithelium is high in the lower part of the
animals, almost obliterating the lumen, but it is low above the tentacles and thus leaves
adistinct cavity. The proboscis contains only stenoteles and isorhizas. The desmo-
nemes are confined to the tentacles. The proboscis is very extensible and can bend to
all sides. It acts like a central tentacle and it is used for locomotion and food capture.
Swedmark (1959) mentions without further comment that Psammohydra produces a
single egg only.
DISTRIBUTION:Western Baltic Sea (Schulz, 1950b), English Channel (Teissier,
1965); western Mediterranean (Swedmark, 1956), Adriatic Sea (Salvini Plawen, 1966).
REMARKS:The taxonomic position of this simplified animal is unclear (see also
remarks for family Acaulidae and Boreohydridae).
FAMILYPROTOHYDRIDAE Allman, 1888
TYPE GENUS:Protohydra Greeff, 1869.
DIAGNOSIS:Solitary,small, elongated hydroids usually living in brackish-
waters; without tentacles and gonophores, pedal disc formed by epidermal cells only;
337
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 5
Psammohydra nanna Schulz, 1950, redrawn from Schulz (1950b), no scale given. A-C) Animals
on sand-grains in various states of contraction. D) Vegetative reproduction by transverse fission.

gametes bulging into gastric cavity, nematocysts: stenoteles and isorhizas, evenly dis-
tributed over body.
Genus Protohydra Greeff, 1869
TYPE SPECIES:Protohydra leuckarti Greeff, 1869.
DIAGNOSIS:With the characters of the family.
REMARKS:Due to their – likely secondary – very simple morphology, the Proto-
hydridae are difficult to classify. Petersen (1990) treated the family as Capitata incerta
sedis. The cnidome is quite interesting as it lacks desmonemes. This could, however be
due to the absence of tentacles. In Psammohydra nanna,asimilarly reduced form, the
desmonemes are associated with the tentacles. The family currently comprises two
species: Protohydra leuckarti Greeff, 1869 and Protohydra psamathe Omer-Cooper,
1964. Protohydra caulleryi Dawydoff, 1930, characterized by budding or frustules, is
likely a polyp belonging to the Oliandiasidae (Weill, 1935; Schulz, 1952).
Protohydra leuckarti Greeff, 1869 Fig. 6
Protohydra leuckarti Greeff, 1869: 37, pls 4-5; Luther, 1923: 1, figs 1-11; Koller, 1927: 97, figs
1-2; Westblad, 1930a: 1-4; Westblad, 1930b: 1-13, figs 1-3; Weill, 1934: 448; Weill,
1935: 83, fig. 5; Westblad, 1935: 152, figs 1-4; Vervoort, 1946: 47, fig. 1; Schulz, 1950a:
53; Nyholm, 1951a: 529, pl. 1; Naumov, 1969: 593, fig. 439; Clausen, 1971: 1.
MATERIAL EXAMINED:ZMUV, Denmark, Mariagerfjord, Ajstrupbugt, 0.5 m, 31 July
1955, 3 specimens, det. Kramp. – IRSN, two samples from Roscoff, collected by J. Bouillon in
May 1964 (many specimens) and August 1961 (few specimens).
DIAGNOSIS:Solitary,small, elongated hydroids without tentacles and gono-
phores, gametes bulging into gastric cavity; vegetative reproduction usually by trans-
verse fission or rarely by lateral buds; nematocysts: stenoteles and isorhizas.
DESCRIPTION:Solitary,brackish-water hydroids, usually elongate spindle- to
club-shaped when relaxed, spherical when contracted. Tentacles absent, at aboral end
asmall epidermal attachment disc for temporary attachment, no perisarc, nematocysts
evenly distributed in epidermis, not concentrated around mouth. Vegetative repro-
duction by transverse fission, rarely by buds (Schulz, 1952). Gonophores absent,
gametes differentiate from epidermal cells and proliferate into gastric cavity where the
gonad remains attached along one side of the body wall, gonochoristic, females pro-
duce one egg only which is expelled by perforation of the body wall. Nematocysts
(Luther, 1923; Weill, 1934; Schulz, 1950b): stenoteles and basitrichous isorhizas,
desmonemes absent.
DIMENSIONS:Adults maximally contracted to a sphere 0.4 mm, expanded
2-3 mm (Greeff, 1869). Eggs ca. 0.25 x 0.14 mm (Westblad, 1930b). Nematocysts
(Luther, 1923): stenoteles 12-17 µm long, isorhizas (7)x(3-3.5)µm,
ADDITIONAL DATA:There are pigment granules of variable size in the gastro-
dermis. The colour of the animals depends on the food items and is either colourless or
various shades of red (Greeff, 1869; Madsen, 1939). Westblad (1935) showed that the
germ cells originate from epidermal cells that proliferate into the gastric cavity.The
animals are gonochoristic and females produce a single egg. The egg is expelled by a
P.SCHUCHERT
338

rupture of the body wall and the animal dies afterwards. Westblad (1935) also made
some observations that hint at a possible copulation. This is rather exceptional for
hydrozoans and needs reconfirmation. Schulz (1952) observed that besides the usual
transverse fission, rarely some animals produce lateral polyp buds. Further biological
data are also provided by Muus (1966) and Wehling (1978). Some information on the
histology – e. g. the body wall, the glue cells, and gametogenesis – are provided by
Luther (1923) and Westblad (1935).
BIOLOGY:A coastal, euryhaline species occurring in brackish waters of wave
protected habitats, often in closed bays, estuaries, and lagoons. It is absent from
agitated waters. The depth range is from a few cm to about 20 m and the reported
salinity range 0.38-30‰ (Westblad, 1930a; Madsen, 1939; Schulz, 1950a; Schönborn
et al.,1993, Barnes, 1994). Various bottom types have been reported, but there seems
to be a preference for fine sand or mud with much detritus. They can reach very high
densities, reaching from 1000 individuals per square metre in winter to 50'000 in
339
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 6
Protohydra leuckarti Greeff, 1869. A-D) Animal in various states of contraction, oral end up-
wards, scale bar approximately 0.2 mm, redrawn from Greeff (1869). E) Schematic longitudinal
section of male animal, the gonads (stippled) bulge into the stomach lumen, scale bar 0.1 mm,
redrawn from Westblad (1935).

summer, or even exceptionally 200'000/m2(Heip, 1971). Rarely it also occurs on
algae. It can be found all year round, but reaches maximum densities in summer when
it also gets sexually mature. Protohydra leuckarti is an important predator in its biotope
and it regulates the density of other animals (Heip, 1971; Heip & Smol, 1976). The
animal is able to creep and to burrow. It lives on a variety of food items, especially
nematodes, copepods, ostracods, chironomid larvae (Schulz, 1950a). It is preyed upon
by e. g. nudibranchs (Evertsen et al., 2004).
DISTRIBUTION:Circumglobal in temperate brackish waters of the northern hemi-
sphere. The northern limit in Europe is southern Norway (Oslofjord: Christiansen,
1972) and southern Finland (Helsinki: Schneider, 1927). It has been reported from the
Atlantic coast of Sweden (Westblad, 1930a); the Baltic Sea (Schneider, 1927;
Westblad, 1935; Koller, 1927; Nyholm, 1951; Schulz, 1950a); Denmark (Madsen,
1939; Muus, 1966; Rasmussen, 1973); German part of the North Sea (Schulz, 1950a);
Holland (Boaden, 1976); Belgium (Greeff, 1869; Heip, 1971); Southern England
(Baker,1913; Hickson, 1920); Brittany (Teissier, 1965); Bay of Biscay (Nyholm,
1951a); in the Mediterranean it was found in brackish water lakes of southern France
(Nyholm, 1951a). It has also been found in the Black Sea (Valkanov,1947; Marcoci,
1956). Outside Europe it has been recorded on the east coast of North America
(Ruebush, 1939), in the north-eastern Pacific (Wieser, 1958), the north-western Pacific
(Naumov, 1969), and the Aral Sea (Maier, 1974). Type locality: Ostende, in mud
among oyster cultures.
FAMILY CANDELABRIDAE STECHOW, 1921
TYPE GENUS:Candelabrum de Blainville, 1830: 284.
SYNONYMS:Myriothelidae Hincks, 1868; Symplectaneidae Fraser, 1941.
DIAGNOSIS:Large, worm-like hydroids, solitary or forming small pseudo-
colonies through connected aggregates, attached to substrate but without stolons;
hydranth elongated, cylindrical to club-shaped; with numerous scattered, hollow or
parenchymatic capitate tentacles, tentacles simple or compound, if compound then
with adnate basal parts. Hydrocaulus with or without perisarc, with tentacle- or root-
like attachment-processes. Gonophores fixed sporosacs, developing either directly on
hydranth body or on club-shaped blastostyles.
REMARKS:Stechow (1921: 248) pointed out that the genus Candelabrum de
Blainville, 1830 has priority over Myriothela Sars, 1850. Consequently, he then also
changed the family name from Myriothelidae Hincks, 1868 to Candelabridae Stechow,
1921. According to the ICZN [4th ed. 1999, 40.2] such a name change is valid if it was
made before 1961 and if the new name has been widely used. The name Candelabridae
has only recently come into usage (e. g. Bouillon, 1985; Schuchert, 1996; Hewitt &
Goddard, 2001), while other used Myriothelidae (e. g. Calder, 1972; Millard, 1975;
Petersen, 1990). I therefore suggest that for the sake of nomenclatural stability,
Candelabridae should be used from now on. This name matches the genus name and it
is also used in several large electronic databases. If in future Candelabridae should not
become the prevailing name, then a ruling of the International Commission on
Zoological Nomenclature must be requested.
P.SCHUCHERT
340

The family currently comprises the following genera: Candelabrum de
Blainville, 1830; Monocoryne Broch, 1910, and Fabulosus Stepanjants, 1990.
KEY TO THE GENERA:
1a capitate tentacles simple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1b capitate tentacles compound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Monocoryne
2a sporosacs borne on blastostyles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Candelabrum
2b sporosacs borne singly on hydranth body . . . . . . . . . Fabulosus (not in European fauna)
Genus Candelabrum de Blainville, 1830
TYPE SPECIES:Lucernaria phrygia Fabricius, 1780 = C. phrygium (Fabricius, 1780).
SYNONYMS (after Segonzac & Vervoort, 1995): Arum Vigurs, 1850; Myriothela M. Sars,
1850; Spadix Gosse, 1853a; Acandela Stechow, 1920.
DIAGNOSIS:Solitary hydroids or loose aggregates comprising few polyps that
may have a common perisarc base. Hydranth long, cylindrical or club-shaped, upper
part with numerous simple capitate tentacles; at base a foot region, with or without
perisarc sheath, with attachment processes that are either covered with perisarc or
naked and may have a perisarc disc at their end; gonophores are fixed sporosacs borne
on blastostyles developing in region between tentacles and foot. With or without
clasper tentacles that hold developing embryos. Development direct, leading to young
polyps without a planula stage.
REMARKS:Segonzac & Vervoort (1995) recently revised the genus Cande-
labrum,outlining its synonymy and taxonomic history.
KEY TO THE NORTH-ATLANTIC CANDELABRUM SPECIES:
1a sporosacs without nematocyst buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1b sporosacs with nematocyst buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. verrucosum
2a foot large, covered by perisarc sheath, hermaphroditic . . . . . . . . . . . . . . . . . . . . . . . . . 3
2b foot without perisarc sheath, without clasper tentacles, dioecious, deep water or
Arctic form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. phrygium
3a boreal shallow water form, with clasper tentacles holding developing embryos
............................................................C. cocksii
3b deep water form, without clasper tentacles . . . . . C. serpentarii (not in European fauna)
Candelabrum cocksii (Cocks, 1854) Fig. 7
Arum Cocksii Vigurs, 1850: 90, nomen nudum.
Spadix purpurea Gosse, 1853a: 126; Cocks, 1853: 365.
Spadix cocksii – Gosse, 1853c: 386.
Arum cocksii Cocks, 1854: 34, pl. 3, fig. 7-12.
Myriothela phrygia –Hincks, 1868: 77, pl. 12 fig. 3; Allman, 1874: 317; Hardy, 1891: 505, pls
36-37; Hartlaub, 1916: 110, figs 38-39.
[not Candelabrum phrygium (Fabricius, 1780]
Myriothela –Allman, 1876: 549, pls 55-58 [only named Myriothela phrygia in plates].
Arum cocksi –Rees, 1957: 487, figs 37 & 39A-B; Prévot, 1959: 97, pl. 1 fig. 1.
Myriothela cocksi –G. O. Sars, 1874: 130; Bonnevie, 1899: 36; Billard, 1921: 12, fig. 1; Weill,
1934: 373; Manton, 1941: 143, figs 1a-b, 2.
Candelabrum cocksii –Segonzac & Vervoort, 1995: 37, fig. 2c-d, table 1.
MATERIAL EXAMINED:MHNG INVE 36299, France, Roscoff, near Ile Verte, 0 m,
17 September 2004, 3 specimens, fertile, examined alive, one blastostyle used for serial histo-
logical sections, confirming the presence of two male sporosacs and several female ones. –
MHNG INVE 29591, France, Roscoff, near Île Verte, 0 m, 30 March 1998, 2 specimens,
341
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

attachment part lacking, fertile, 28S sequence of this material in GenBank under accession
number AY920796, 18S AY920758, 16S AY787879. – MHNG INVE 35726, France, Roscoff,
Tyaozon, 6 May 1910, coll. M. Bedot. – BMNH 1980.3.1.1, misidentified as Candelabrum phry-
gium,England, Devon, Salcombe, Castle Rock, 19 Feb 1980, R. L. Manuel, 3 well preserved
specimens, eggs held by claspers present, base in irregular perisarc.
P.SCHUCHERT
342
FIG. 7
Candelabrum cocksii (Cocks, 1854); A, after photographs of living animals, C-F,after preserved
material. A) Entire polyp, semi-extended, capitate tentacles contracted, scale bar approximately
5mm. B) Blastostyle with sporosacs and capitula (stippled), scale bar 1 mm. C) Tip of blas-
tostyle with branched end, same scale as B. C) Embryo held by three clasper tentacles, scale bar
1mm. E) Attached base of hydranth, perisarc dark, note two small perisarc discs in lighter
region, scale bar 3 mm. F) Nematocysts of mature polyp: large and small desmonemes, stenotele,
microbasic eurytele, scale bar 10 µm.

DIAGNOSIS:Candelabrum species with clasper tentacles that hold embryos, her-
maphroditic, base long and sheathed in perisarc envelope that is adnately attached to
the substratum.
DESCRIPTION:Solitary, relatively large, firmly attached, worm-like polyps,
divided into three regions: foot, blastostyle region in middle, and trunk.
Foot large, about 1/4 to 1/3 of whole animal, bent horizontally so that attach-
ment to substrate is adnate, basal region encased in firm, brown perisarc, distorted and
gnarled to fit irregularities of the substratum and provided with short, lobed or finger-
like projections with flat ends adhering to the solid substratum; the perisarc gradually
thins out distally; on thinner perisarc region there can be a few thick, sharply demar-
cated perisarc discs used for attachment, but without being associated with notable
protrusions of the hydranth wall; further distal some short finger-like protrusions of the
hydranth wall can occur.
Blastostyle region of about the same length as foot, provided with numerous
(>20-40), widely spaced blastostyles bearing the gonophores and with thin clasper
tentacles holding embryos. Blastostyles contractile, hollow and lumen in connection
with gastric cavity, stick- to club-shaped (swollen distally), sometimes branched in
distal region, distal region provided with nematocyst clusters, these in hemispherical
bumps or stubby capitate tentacles with short thick pedicels, quite irregular in
appearance; proximal 2/3 of blastostyle with irregularly scattered gonophores, different
developmental stages mixed. Gonophores are fixed sporosacs without radial canal
system (cryptomedusoid type); males and females occurring on same blastostyle, the
animals are thus simultanous hermaphrodites. Sporosacs spherical, white, female ones
larger than male ones, females initially with numerous small oogonia but ultimately
only one egg matures. Mature or fertilized eggs leave sporosac but are then grasped by
two to five clasper tentacles. Clasper tentacles thin, straight, of variable length, ori-
ginating in pairs or more at bases of blastostyles or also independently of them, without
nematocysts, terminal region sucker-like, enlarged, and attached to the envelope of
developing eggs.
Trunk region comprising about half of the animal, capable of great expansion
and strong contraction, elongate club-shaped with largest diameter following the
blastostyle region, evenly and entirely covered by hundreds of imbricate, indistinctly
capitate tentacles; capitate tentacles contractile, hollow, pedicel short in material taken
out of the sea (even when anaesthetized, but can extend considerably in undisturbed
specimens and become distinctly capitate), capitulum ovoid, diameter not much larger
than the contracted pedicel.
The foot and blastostyle parts are less contractile than the trunk. In animals
which have been preserved without relaxation, the trunk region is thus only as large or
smaller than either the foot and blastostyle region. The long foot is characteristic for
this species (comp. Figs 7 and 8-9).
Nematocysts of mature animals: two types of desmonemes, stenoteles, micro-
basic euryteles. In young polyps, there are also isorhizas (Weill, 1934); they may also
be found rarely in adults (own observations).
Colours: living animals entire body, blastostyles, and sporosacs white, capitula
of tentacles of trunk purple, perisarc dark amber-brown.
343
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

DIMENSIONS:Mature body size variable and difficult to establish due to great
contractibility, ranging from a few cm to 12 cm, reportedly also more, usually 2-3 cm
when contracted; blastostyles up to 4 mm but contractile; capitula of trunk tentacles
diameter about 0.2 mm, expanded tentacles up to 2 mm long (Allman, 1874); clasper
tentacles 1-2 mm long; diameter of fertilized eggs held by claspers 0.7-0.8 mm, female
sporosacs reach same diameter; male sporosacs smaller, 0.30-0.42 mm (Segonzac &
Vervoort 1995). Nematocysts of mature animal (preserved material, see Fig. 7F): large
desmonemes (12-14)x(8.5-9.5)µm; small desmonemes (7.5-9)x(5-6)µm; stenoteles
(11-11.5)x(8-9)µm; microbasic euryteles (18-20)x(5.5-6)µm, ratio of everted shaft to
capsule length around 0.9; presumed isorhiza 13.5x5 µm.
BIOLOGY:Along the coasts of Brittany, fertile animals have been documented
from January to September (Teissier, 1965; Castric-Fey, 1970, own data), but likely
some animals are reproductive all year round. Asexual reproduction may take place by
budding small polyps at the junction of the foot and blastostyle region (Hardy, 1891;
Hartlaub, 1916). This asexual budding takes place before the onset of sexual repro-
duction in early spring (Hardy, 1891).
The animals occur at the spring tide low-water-mark, but records down to 17 m
are known (Castric-Fey, 1970; Segonzac & Vervoort, 1995). Sars (1874) gives a depth
of 110-146 metres for his record from the Aalesund, which is unusually deep for this
animal. Intertidally,the species occurs attached on the underside of large boulders.
They can also be attached to holdfasts of laminarians (Castric-Fey, 1970). Billard
(1921) made some preliminary observations on their feeding biology. With their much
extensible trunk they search their surroundings for small benthic amphipods. It takes
about five to six hours to digest one of them. The animals are also able kill shrimps of
up to 2 cm size.
The embryonic development takes place in the embryonic envelope that is held
by the clasper tentacles. The animal can thus be considered an actively brooding
species. The clasper tentacles only attach to fertilized eggs, as only these form the nec-
essary embryonic envelope (Beigel-Heuwinkel, 1988). The development results in a
young polyp with 17-22 tentacles (Billard, 1921). The primary tentacles of the young
polyp are only transitory and are replaced by permanent tentacles. More details on the
development are given in Allman (1876, as Myriothela), Billard (1921), Benoît (1923a,
1925), and van der Vyver (1968).
ADDITIONAL DATA:The gastrodermis has numerous folds and villi (cylindrical
projections), but has no compartmentalization as in the Tubulariidae (Allman, 1876).
The mesogloea is massive and contains thick fibres (Beigel-Heuwinkel, 1982a). It is
also involved in the attachment to the substratum (Manton, 1941). Histological details
can be found in Allman (1876, as M. phrygia)and Hardy (1891, as M. phrygia). The
tentacles are hollow.Prévot (1959) shows them as closed offto the gastric lumen by a
mesogloeal lamella, but Allman (1876, pl. 56, fig. 2) states that they are open. An
examination of some hand-made cross-sections of the available material showed that
there are indeed small openings, but this should be corroborated by more reliable
evidence obtained by serial histological sections. The strong contractibility of the
tentacles may be regulated by the hydrostatic pressure of the water in the lumen of the
P.SCHUCHERT
344

tentacles. If so, an opening to the stomach seems more understandable. The initial
tentacles formed while the embryo is still in the egg capsule develop towards the
gastric lumen and are only everted at a later stage (Allman, 1876). The primary
tentacles must thus have a basal opening. The primary tentacles are quite long and
replaced after hatching by shorter tentacles (Allman, 1876).
The sporosacs and their development have been examined by Allman (1876, as
M. phrygia), Korotneff (1888), Hardy (1891, as M. phrygia), Benoît (1923b), and
Beigel (1976). Manton (1941) studied the foot and the clasper tentacles. The clasper
tentacles were also investigated by Beigel-Heuwinkel (1988). She used light and
electron microscopic data to show that the cells at the tip secrete a substance that acts
to glue the claspers to the embryonic envelope. Unfertilized eggs do not form an
embryonic envelope and are thus not held by the claspers.
Results of regeneration experiments were reported by Billard (1921) and
Beigel-Heuwinkel (1982b). Regenerating upper halves of a polyp form no perisarc
sheath, but anchoring tentacles as in C. phrygium.
DISTRIBUTION:North-Eastern Atlantic, absent from the North Sea, Baltic Sea,
Mediterranean and Black Sea. The northernmost record is Norway (Aalesund,
G. O. Sars, 1874; somewhat doubtful, needs reconfirmation), common in the western
English Channel coast of Great Britain and France, also recorded from the Scilly
Islands, Isle of Man, western England, southern Brittany,Galicia, Bay of Cadiz (south-
ernmost record) (Segonzac & Vervoort, 1995, Medel & López-González, 1996, this
study). Type locality: Gyllyngvase, (Gwyllyn-vase in Cocks, 1850), Falmouth,
Cornwall, United Kingdom.
REMARKS:Candelabrum cocksii has usually been attributed to Vigurs (1849),
but that is incorrect. The binomen Arum cocksii was introduced in a paper by Cocks
that almost certainly appeared in 1850 and not 1849 (Cornelius, 1977). Cocks
attributed the name to Vigurs without providing a description. It is thus an invalid name
(nomen nudum). Furthermore, it seems that Cocks initially did not recognize it as a
hydrozoan as he placed it among the Sipuncula. Gosse (1853a: 126) then published the
name Spadix purpurea,of which Cocks (1853: 365) acknowledged in the same journal
that it is identical to his Arum cocksii.Cocks (1853) used Spadix purpurea as species
name followed by Arum cocksii in brackets to formalize the synonymy. A suitable
description and figures of Arum cocksi followed shortly afterwards in Cocks (1854),
which made the name formally available for the first time [ICZN, 1999, 4th ed., 50.1]
[the publication date of Cocks’s paper is somewhat unclear, it could be 1853 or 1854;
according to Cornelius (1977) it was likely 1854]. Gosse (1853c: 386) acknowledged
the synonymy and he apparently ceded his species designation to Cocks by the
footnote ".....I gladly recognise, however, the superior claim [of Cocks] of the specific
appellation, which pays a deserved compliment to an excellent naturalist."
Although Spadix purpurea Gosse, 1853 is likely a senior synonym of Arum
cocksii Cocks, 1854, the combination Candelabrum cocksii (Cocks, 1854) must be
taken as valid, this because to my knowledge Gosse's name has not been used as valid
after 1899 [ICZN, 1999, 4th ed., 23.9.1.1], while C. cocksii has been used regularly (see
Vervoort & Segonzac, 1995).
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

Candelabrum cocksii (Cocks, 1854) has unfortunately been confounded with C.
phrygium (Fabricius, 1780) by Hincks (1868), Allman (1876), and many subsequent
authors relying on Hincks (see Vervoort & Segonzac (1995) for synonymy and
misidentifications). Recently, Cornelius (1977) again maintained that both are conspe-
cific. Cornelius based his claim by referring to other authors, e. g. Stechow (1923) and
Teissier (1965). These two authors, however, do not claim such a synonymy, and
Stechow even advocates a separation at the genus level. The opinion of Cornelius is
also not shared by Segonzac & Vervoort (1995) as well as by the present author. Both
species are clearly separable. Candelabrum cocksii and C. phrygium differ in the foot
morphology (long, perisarc covered foot versus short, naked one); clasper tentacles
(presence versus absence), and the sexual reproduction (hermaphroditic versus gono-
choristic).
The tentacles of the trunk are usually short and only indistinctly capitate, this in
preserved material as well as in living material taken into the laboratory. The tentacle
pedicels are very contractile and undisturbed animals have quite long tentacles (2 mm;
Allman, 1874). This has also been observed for the closely related species C. serpen-
tarii (see figs 3A-B in Segonzac & Vervoort, 1995). Candelabrum serpentarii
Segonzac & Vervoort, 1995 is only known from deep waters of the central Atlantic.
This species is also monoecious, but lacks clasper tentacles and its eggs are four to five
times larger. The only Candelabrum species that also has clasper tentacles is the Pacific
Candelabrum fritchmanii Hewitt & Goddard, 2001. This species can form colony-like
aggregates, a unique feature within this genus.
Candelabrum phrygium (Fabricius, 1780) Fig. 8
Lucernaria phrygia Fabricius, 1780: 343.
Myriothela arctica M. Sars, 1850: 14.
Myriothela phrygia – Sars, 1877: 23, pl. 2 figs 29-36; Bonnevie, 1899: 35, pl. 4 figs 5-6;
Jäderholm, 1908: 9, pl. 1 fig. 7; Broch, 1916: 19, fig. C, pl. 1 figs 3 & 8; Rees, 1957: 486,
fig. 36; in part Naumov, 1969: 261, not figures; Calder, 1972: 222, pl. 1 fig. 5.
?Myriothela gigantea Bonnevie, 1898a: 490, pl. 27 figs 46-47; Bonnevie, 1899: 38, pl. 4 fig. 1.
?Myriothela minuta Bonnevie, 1898a: 489, pl. 27 fig. 44; Bonnevie, 1899: 37, pl. 3 fig. 6a-b, pl.
4 fig. 4.
?Myriothela mitra Bonnevie, 1898a: 489, pl. 27 fig. 43; Bonnevie, 1899: 38, pl. 3 fig. 6c-e, pl.
4 fig. 3.
Candelabrum phrygium – in part Cornelius 1977: 521 [excl. synonymy]; Segonzac & Vervoort,
1995: 45, figs 2e-f, 3E-F, table 1 [some references do not refer to this species];
Schuchert, 2001a: 37, fig. 24.
MATERIAL EXAMINED:Re-examined material mentioned in Schuchert (2001a), ZMUC,
Greenland, no exact locality and date known, collected by Lüthken, identified by P.Kramp, two
specimens, both broken into two parts, one obvious female on branching bryozoan (Cellariidae),
other animal on red algae, previously identified as male; one blastostyle of both specimens was
used for serial histological sections, both specimens proved to have female sporosacs only,
though the tissue preservation is not good. – All suitable material found in the BMNH that is la-
belled as C. phrygium turned out to be C. cocksii.
DIAGNOSIS:Candelabrum species without clasper tentacles, dioecious, basal
foot short or absent, straight and not sheathed in perisarc envelope, attached to sub-
stratum by tentacle-like filaments usually ending in perisarc discs.
P.SCHUCHERT
346

DESCRIPTION (after Sars, 1877; Segonzac & Vervoort, 1995; own data): Polyp
solitary, worm-like, size very variable as able to expand and contract enormously.
Hydranth shape also variable, usually cylindrical to conical, subdivided into a distal
tentaculate region (trunk), followed by a blastostyle region and sometimes also a foot
zone.
Foot zone either very short in relation to other parts or absent, not curved,
adhering to substratum by several tentacle-like attachment filaments, each of them with
terminal region sucker-like and enlarged, attached to a perisarc disc that adheres to sub-
stratum, perisarc discs sometimes absent.
Blastostyle region about 1/4 to 1/3 of contracted polyp, beset by many (>20)
club-shaped blastostyles. At distal end of blastostyles four to six nematocyst clusters in
wart-like tubercles. Blastostyles bear sessile sporosacs, the two sexes on different
polyps, sporosacs without nematocyst tubercles. Male sporosacs spherical, without
radial canals, up to 50 per blastostyle at different developmental stages. Females with
two to six sporosacs per blastostyle, maximally two mature, others in development,
spherical, no radial canals, initially many eggs but presumably only one egg per
sporosac attains maturity,fertilized in situ and developing into a young polyp, hence
viviparous.
347
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 8
Candelabrum phrygium (Fabricius, 1780), after preserved material from Greenland. A) Entire
polyp, scale bar 2 mm. B-C) Blastostyles, scale bar 0.5 mm.

Trunk region comprising majority of hydranth length, with numerous (>200)
capitate tentacles, these hollow, extensible, capitula ovoid.
Colours: cream-white. Nematocysts: stenoteles; ? haplonemes; desmonemes of
two size classes.
DIMENSIONS: Height of contracted specimens 2-6 cm, expanded up to 30-40 cm
(Bonnevie, 1899; Broch, 1916), width a few mm. Diameters of male sporosacs 0.4-0.8
mm when mature, females 0.9-1.4 mm. Capitate tentacles with stalk 0.3-0.5 mm,
capitula 0.17-0.25 mm (Segonzac & Vervoort, 1995). Nematocysts (Segonzac &
Vervoort, 1995): stenoteles (10.6-11.5)x(8.2-9.8)µm; ? haplonemes (19.7-20.5)x(8.2-
9.9)µm; desmonemes of two size classes (12.5-13.0)x(9.0-9.8) µm and (8.2-9.0)x(6.4-
6.6) µm.
BIOLOGY:Occurs usually at considerable depths of several hundreds of meters
down to 2195 m (Bonnevie, 1899), but in the high Arctic it as been found as shallow
as 13 m (Jäderholm, 1908). The polyps live permanently attached to solid substrata like
rock, bivalves, hydroids, bryozoans, and algae. The animals are viviparous and lack a
planula phase (Sars, 1877; Schuchert, 2001a); the newly released polyp is spherical
and has 20-30 capitate tentacles. The tentacles formed while the embryos is still in the
egg capsule develop inverted into the gastric lumen, but evert before hatching.
DISTRIBUTION:An Arctic, deepwater species penetrating into boreal regions, in
European waters reaching as far south as the Trondheimfjord and the Wyville-
Thomson-Ridge between Scotland and The Faeroes (Broch, 1903; Broch, 1916).
Segonzac & Vervoort (1995) report a find from the Mid-Atlantic Ridge south-west of
the Azores in a depth of 1622 m, wich is the southernmost record of this species. It has
also been recorded in northern Norway (Sars, 1877; Bonnevie 1899), Jan Mayen
(Broch, 1916), Russian Arctic Seas (Jäderholm, 1908; Naumov, 1969), northern Pacific
(Naumov, 1969). Also known from Iceland (Broch, 1916), Greenland (Schuchert,
2001a), Canada (Calder, 1972). (Note that numerous other records under this name
from costal regions of the NE Atlantic refer in fact to Candelabrum cocksii). Type
locality: Greenland.
REMARKS:The synonymy of this species has been worked out quite thoroughly
(Sars, 1877; Bonnevie, 1899; Segonzac & Vervoort, 1995). Myriothela arctica Sars,
1850 was synonymized by Sars himself after he had re-examinated Fabricius’ type
material (Sars, 1877). The boreal shallow-water species Candelabrum cocksii has often
been synonymized with this species, but this is not tenable (see under C. cocksii). Some
of Bonnevie’s Candelabrum species (C. minutum,C. mitra,C. giganteum)are not well
characterized and might also belong to this species (Rees, 1956). They are here listed
as questionable synonyms (see also Segonzac & Vervoort, 1995). The material on
which these three species were based, already fragmentary when examined by
Bonnevie (1899), is now in such a bad condition that it is virtually useless (Rees,
1956). Contrary to the view of Rees (1956), Candelabrum verrucosum (Bonnevie,
1898) is well characterized and it is re-described below.
Candelabrum phrygium is portrayed as being dioecious, but for preserved
material it is often difficult or impossible to determine the sex. This is easy only for
P.SCHUCHERT
348

well advanced female sporosacs as they contain young polyps. For a reliable sex de-
termination, serial histological sections must be made. One blastostyle of each of the
two specimens examined for this study was thus used to make serial sections. Both
animals had female sporosacs only. One specimen did not have sporosacs with
advanced embryos and was thus initially mistaken for a male (Schuchert, 2001a). This
shows that sex identifications of preserved material are often unreliable. More inves-
tigations using histological sections of entire blastostyles are desirable to confirm that
C. phrygium is always dioecious (comp. C. verrucosum).
The material examined in this study and also by other authors (Sars, 1877) had
attachment tentacles that were cemented to the substratum by distinct perisarc discs
that adhere tightly to the substratum and cannot be removed without destroying them.
Dislodged hydranths lack them regularly. Sometimes they are quite thin and incon-
spicuous and if attached on rock they might be hardly visible. This could explain that
some investigators did not find them (e. g. Segonzac & Vervoort, 1995), but is well
possible that they can also be absent.
Candelabrum verrucosum (Bonnevie, 1898) Fig. 9
Myriothela verrucosa Bonnevie, 1898a: 468, pl. 27 fig. 45; Bonnevie, 1899: 37, pl 4, fig. 2.
Candelabrum verrucosum –Segonzac & Vervoort, 1995: 53.
MATERIAL EXAMINED:ZMUC, Kap Farvel expedition station 148, 60.07°N 43.20°W
(Greenland), 50 m, 27 August 1966, from rocky bottom, fertile female with sporosacs contain-
ing embryos, tissues somewhat shrunken. Two blastostyles were used to make serial histological
sections, confirming the presence of male and female sporosacs.
DIAGNOSIS:Candelabrum species with sporosacs bearing scattered nematocyst
buttons on their surface, monoecious, no clasper tentacles; foot straight, not covered by
perisarc, attached via attachment filamants; size 1-4 cm.
DESCRIPTION (after examined specimen): Solitary polyp, 1.1 cm, cylindrical,
divided into three regions: distal tentaculate region (trunk), followed by a blastostyle
region and a foot zone.
Foot zone about 1/6 of animal, straight, with several (>10) tentacle-like attach-
ment filaments of variable length, some of them with enlarged, sucker-like ends; one
filament with terminal perisarc disc, those of other filaments presumably lost.
Blastostyle region taking up about half of the polyp, bearing many (>20) club-
shaped blastostyles, clasper tentacles absent. Nematocyst clusters in wart-like tubercles
at distal end of blastostyles. Blastostyles bear several (up to 8) sessile sporosacs.
Sporosacs with up to eight distinct nematocyst buttons on surface, no radial canals or
ring canals present. Largest sporosacs contain a single young polyp, animal thus
viviparous. Besides female sporosacs, there is also one male sporosac per blastostyle,
animals thus simultanous hermaphrodites.
Trunk region about 1/3 of hydranth length, covered by numerous (>100) capi-
tate tentacles, their capitula ovoid.
Nematocysts (not well preserved): stenoteles, large desmonemes, ? hetero-
nemes.
DIMENSIONS:Hydranth can reach 4 cm (Bonnevie, 1898a), sporosacs up to
0.9 mm, blastostyles up to 2.2 mm, diameter of capitula 0.2 mm.
349
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

ADDITIONAL DATA:The tentacles formed while the embryos is still in the egg
capsule develop inverted into the gastric lumen, but evert before hatching.
DISTRIBUTION:Northern Norway, Southern Greenland (this study). Type
locality: Norway,Hammerfest (Bonnevie, 1899).
REMARKS:Candelabrum verrucosum (Bonnevie, 1898) has hitherto been
known from one specimen described by Bonnevie (1898a, 1899). Some authors
doubted its validity and thought it might belong to C. phrygium (e. g. Rees, 1956). The
species is characterized by sporosacs that bear scattered buttons of nematocyst clusters.
This is quite a unique feature and has never been observed for C. phrygium.Iam
convinced that C. verrucosum is a valid species, distinct from C. phrygium, and that
the material described above belongs to it. The characteristic nematocyst buttons on the
sporosacs are quite conspicuous in material examined with a dissecting microcope.
There are a few discrepancies from the original material described by Bonnevie
(1898a): there are more than two sporosacs per blastostyle, the blastostyle region is
larger,and the animal is smaller.As these traits show considerable intraspecific
variation in other Candelabrum species, they are here also considered as such.
Candelabrum verrucosum is easily distinguished from C. phrygium by the
nematocyst buttons on the sporosacs, but it differs additionally by being monoecious.
Otherwise, both species are very similar. Only two blastostyles could be used to make
serial histological sections. Both blastostyles had female sporosacs of all develop-
P.SCHUCHERT
350
FIG. 9
Candelabrum verrucosum (Bonnevie, 1898), after preserved material from Greenland. A) Whole
animal, the blastostyle region covers slightly more than half of the animal, note the nematocyst
buttons on the sporosacs, scale bar 2 mm.

mental stages (some containing almost fully formed young polyps) and a single male
sporosac filled with spermatids. The male sporosacs are smaller than the female ones.
Genus Monocoryne Broch, 1910
TYPE SPECIES:Coryne gigantea Bonnevie, 1898b.
SYNONYMS:Symplectanea Fraser, 1941 (see Rees, 1958).
DIAGNOSIS:Hydroid solitary or a few polyps in loose aggregates that may have
acommon perisarc base. Hydranth long, cylindrical, divided into tentaculate body and
foot region. Foot covered by thin perisarc, with root-like attachment processes.
Hydranth body with scattered capitate tentacles, at least some of them compound
tentacles, i.e. branched tentacles with a common epidermis at the base, bases of the
side-branches adnate to the side of the main tentacle for some distance, all ends capi-
tate. Gonophores fixed sporosacs developing directly on hydranth body, associated or
not with tentacles.
REMARKS:For more details consult Rees (1956, 1958), Petersen (1990), or
Stepanjants et al. (2003). The European fauna comprises one species only. Stepanjants
et al. (2003) give an overview on all species.
Monocoryne gigantea (Bonnevie, 1898) Fig. 10
Coryne gigantea Bonnevie, 1898b: 4, pl. 1 fig. 1.
Monocoryne gigantea –Broch, 1910: 138; Broch, 1916: 12, pl. 1 fig. 1; Johannesen, 1924: 1,
figs 1-7, pl. 1-2; Rees, 1956: 117, figs 1-2; Rees, 1957: 488, fig. 38; Calder, 1972: 222,
pl. 1 fig. 4; Antsulevich, 1988: 931, fig'd; Petersen, 1990: 203; Stepanjants et al., 2003:
100, figs 1A-F, 6.1.
DIAGNOSIS:Monocoryne species up to 15 mm; compound tentacles with two to
four capitate ends, usually three; hermaphroditic, sporosacs in upper axils of
compound tentacles.
DESCRIPTION:(after Bonnevie, 1898b; Johannesen, 1924; Rees, 1956;
Stepanjants et al., 2003) Vermiform hydranths, solitary or clustered into loosely joined
aggregates, attached laterally to substratum by curved proximal end; divisible into foot
(caulus) zone and tentaculate part. Foot roughly 1/2 of total length, covered by close
fitting, soft, thin perisarc, in lower half of foot several large, distinct anchoring
filaments with widened distal end. Tentaculate part also about 1/2 of length, but very
extensile and active in life, all tentacles distinctly capitate with spherical capitula, very
extensible, around mouth about eight simple capitate tentacles, below them many
(< 30) scattered compound tentacles and also some simple ones. Compound tentacles
usually with three, sometimes two or four capitate ends, with middle branch(es)
thickest and longest, the side-branches originate near its base and are adnate for some
distance before they become free, the fused part forming a plate-like base with a
common epidermis. Gonophores sessile sporosacs arising in the upper axils of the
compound tentacles, sporosacs oblong, without radial canals; male, female and herma-
phroditic sporosacs can be produced by the same animal (Broch, 1916; Johannesen,
1924). Nematocysts: stenoteles, microbasic mastigophores, desmonemes, microbasic
euryteles.
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

DIMENSIONS (Rees, 1956; Stepanjants et al.,2003; consult these references for
additional measurements): Fertile polyps 11-15 mm (preserved material), diameter of
hydranth body 1.4-1.7 mm, length of gonophores 0.6-0.9 mm, diameter 0.4-0.5 mm.
Nematocysts: stenoteles (14-18)x(12-18) µm; microbasic mastigophores (19-24)x(8-
11) µm; desmonemes 10x8 µm, microbasic euryteles (22.5-25)x(12-12.5) µm.
BIOLOGY:Arare species, occurs usually in waters of 100 m depth and more, but
in the high Arctic archipelago Franz Joseph Land it was found in only 16-20 m
(Antsulevich, 1988). Known substrata (Swenander, 1904) are a Tubularia spec. and
polychaete tubes, both attached on shells of the bivalve Lima excavata.
DISTRIBUTION:Arctic species, with its southern limit in the Trondheimsfjord
(Johannesen, 1924). It has been recorded from northern Norway (Bonnevie, 1898b),
P.SCHUCHERT
352
FIG. 10
Monocoryne gigantea (Bonnevie, 1898), modified from Rees (1956). A) Whole polyp, foot with
perisarc stippled dark. B) Compound tentacle. C) Side view of sporosac in axil of compound
tentacle.

Franz Joseph Land (Antsulevich, 1988), North-Eastern Canada (Calder, 1972). Type
locality: Hammerfest, Norway.
REMARKS:Rees (1958) synonymized the genera Symplectanea and Mono-
coryne,but kept M. bracteata provisionally distinct from M. gigantea because of its
larger size and the greater number of capitate heads per compound tentacles, but he
suggested that more material might show it to be synonymous with M. gigantea.It
could be that Monocoryne bracteata is dioecious, thus differing from the monoecious
M. gigantea.The only other named species of the genus is Monocoryne minor Millard,
1966. It is smaller and its sporosacs develop independently of the tentacles.
FAMILY TRICYCLUSIDAE KRAMP, 1949
DIAGNOSIS:Solitary, usually benthic hydroids, having a conical to pear-shaped
hydranth and tapering pedicel ending in a small attachment disc. Pedicel covered in a
loose, filmy or gelatinous perisarc. Tentacles in three whorls, one oral whorl, one in
middle of hydranth body, and one near base of body. Oral tentacles capitate, other
tentacles also capitate but bearing additional nematocyst clusters. Vegetative budding
of hydranths below proximal tentacles. Gonophores develop above proximal set of
tentacles and remain fixed. Male gonophores medusoid, with radial canals and circular
canal. Female ones without canal system. Cnidome: Stenoteles, desmonemes, and
heteronemes.
Genus Tricyclusa Stechow, 1919
TYPE SPECIES:Tiarella singularis Schulze, 1876.
SYNONYM:Tiarella Schulze, 1876.
DIAGNOSIS:As for the family.
REMARKS:The genus Tricyclusa is currently monotypic, containing only
Tricyclusa singularis (Schulze, 1876). Schulze (1876) originally proposed the genus
name Tiarella for this species. Because this name is preoccupied for a gastropod and
also other taxa, Stechow (1919: 6) proposed the new name Tricyclusa.It is a charac-
teristic genus and it poses no taxonomic problems.
Tricyclusa singularis (Schulze, 1876) Fig. 11
Tiarella singularis Schulze, 1876: 415, pls 29-30; Bedot, 1911: 209, pl. 11 fig. 2.
Tricyclusa singularis –Stechow, 1919: 6; Rees, 1941: 133, fig. 3; Rees, 1957: 462, 505, figs 6
&51B; Picard, 1957: 10; Vevers, 1959: 506, figs 1-6; Teissier, 1965: 10; Bouillon, 1974:
142; Petersen, 1990: 146, fig. 15; Bouillon et al.,2004: 103, fig. 55D.
Margelopsis stylostoma Hartlaub, 1903: 28, fig. 2; Hartlaub, 1907: 91, fig. 87; Bedot, 1911: 211;
Rees, 1941: 133.
MATERIAL EXAMINED:BMNH 1957.6.26.1-10, Roscoff intertidal, leg. Cantacuzène, on
red algae, numerous well preserved specimens. – BMNH 1956.11.7.7-13, Baie de Morlaix, 23
June 1955, coll. W.J. Rees, on Chorda filum,several contracted specimens.
DIAGNOSIS:As for the family.
DESCRIPTION (after literature and observed material): Hydroid solitary, usually
attached to algae, sometimes freely floating, divided into hydranth body and pedicel,
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

both of about the same length. Pedicel in a conical, loose, filmy or gelatinous periderm
cup, wrinkled, with adhering detritus particles. Pedicel tapering proximally,ending at
base in a small attachment disc. Hydranth pear-shaped to conical, broadest near lower
end, with three distinctly separated sets of tentacles, tentacle gastrodermis chordoid.
Oral tentacles in one whorl, four to five in number, short, capitate, directed upwards;
P.SCHUCHERT
354
FIG.11
Tricyclusa singularis (Schulze, 1876), after preserved material. A) BMNH 1957.6.26.1-10,
Roscoff, polyp with long tentacles, scale bar 0.2 mm. B) polyp with short tentacles, after
Petersen (1990), scale bar 0.5 mm. C) Optical section of a female sporosac, modified after Bedot
(1911), scale bar 0.2 mm. D) Optical section of a male medusoid after it has liberated its
gametes, modified after Schulze (1876), scale bar 0.05 mm

middle whorl of tentacles approximately in middle of body, usually six in number,
directed obliquely upwards, with terminal nematocyst knob and with or without addi-
tional one to two knobs in distal half of tentacle; basal tentacles 10 to 14, usually 12,
in two closely approximated whorls, alternately pointing up- and downwards, with
terminal knob and additionally one or more proximal knobs, these either clasping or
encircling tentacle. Underneath lowest tentacles vegetative polyp buds, one to six in
number, budded polyps are released as small, fully formed hydranths but have a short
pedicel, newly released polyps may already have incipient gonophores. Gonophores
develop immediately above basal whorl of tentacles, spherical, remaining attached to
hydroid. Male gonophores with four radial canals and ring canal, thus of medusoid
type. Female gonophores sporosacs without canal system, with one large egg. Nemato-
cysts: Stenoteles, desmonemes, microbasic euryteles.
DIMENSIONS:Total height around 2 mm, hydranth about 1 mm high, hydranth
base diameter 0.4-0.6 mm. Female sporosacs after Bedot (1911) about 0.6 mm, male
medusoids after Schulze (1876) about 0.2 mm.
ADDITIONAL DATA:The length of the tentacles is variable, and this is not only
due to contraction. Young individuals and polyps found in the plankton have very long
and thin tentacles that get shorter once the animal attaches itself (Bedot, 1911). Young
animals and those from the plankton also have a short pedicel.
DISTRIBUTION:Adriatic Sea, Northern Brittany,western Ireland. Type locality:
Adriatic Sea, Trieste, Bay of Muggia (Italy), on Cystoseira.
BIOLOGY:The polyps live attached to various macroalgae and Zostera plants
near the low-water-mark (Rees, 1941, Teissier; 1965). Occasionally, detached polyps
can be found in the plankton, but this is not the usual mode of life (Bedot, 1911). In
Brittany it occurs mainly from May to July, although some animals were also found
during March and April (Bedot, 1911; Teissier, 1965). In the Mediterranean it was
found in April (Schulze, 1876). The fertile period for Brittany is from May to June
(Bedot, 1911; Teissier, 1965). It is a rare species, but when present, it can occur in large
numbers (Bedot, 1911).
REMARKS:Tricyclusa singularis (Schulze, 1876) is a characteristic and un-
problematic species. Hartlaub (1903, 1907) described a similar species from the
plankton of Roscoff which he named Margelopsis stylostoma,differing mainly only in
the short pedicel. Even Hartlaub (1903, 1907) suspected that it was only a planktonic
form of Tricyclusa singularis. It was later synonymized with Tricyclusa singularis by
Bedot (1911) and Rees (1941).
Although easy to identify and despite its presence near the water surface, this
animal has only rarely been reported. After its discovery, it has never been found again
in the Mediterranean Sea. It seems that it is only occasionally present and quite
seasonal. Most regularly it has been seen at Roscoff (Brittany). It is particularly
interesting to note that it has never been reported from the other side of the English
Channel, despite England being one of the best investigated regions. Perhaps it prefers
warmer waters, an assumption also underlined by its occurrence during the summer
months. Probably it survives unfavourable conditions through a sexually produced
resting stage.
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

FAMILY MARGELOPSIDAE UCHIDA, 1927
TYPE GENUS:Margelopsis Hartlaub, 1897.
SYNONYM:Pelagohydridae Dendy, 1902.
DIAGNOSIS:Hydroid solitary, pelagic; hydrocaulus absent or reduced to a small
process; hydranth body vasiform, tentacles filiform to moniliform, arranged into two
separate sets, oral tentacles in one or several whorls; aboral tentacles either in two to
three alternating whorls or numerous and scattered over most of body. Gonophores free
medusae, medusa buds develop among tentacles or above aboral tentacles.
Medusa manubrium with simple mouth; gonads surrounding manubrium
entirely; four radial canals; tentacles solid, generally moniliform, two or more tentacles
per marginal bulb, in some genera tentacles also issuing at different levels on exum-
brella; without ocelli.
REMARKS:With its clustered marginal tentacles in the medusae and the pelagic
polyps, this is a distinct and characteristic family of the Capitata. It comprises the
genera Climacocodon Uchida, 1924, Margelopsis Hartlaub, 1897, and Pelagohydra
Dendy, 1902 (Petersen, 1990). The well established and frequently used name
Margelopsidae Uchida, 1927 is threatened by the senior synonym Pelagohydridae
Dendy, 1902. The latter name has not been used and for the sake of nomenclatural
stability it is preferable to continue to use Margelopsidae. According to the ICZN
[article 29.3.1.1] there is no need to change it to the formally correct Margelopsididae.
KEY TO GENERA:
1a medusa with several tentacle pairs on exumbrella . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
......................................Climacocodon (not in European fauna)
1b medusa tentacles in four groups along bell margin: . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2a polyp with caulus rudiment, aboral tentacles in two to three close whorls . . Margelopsis
2b polyp without caulus rudiment, aboral tentacles scattered . . . . . . . . . . . . . . . . . . . . . . .
.......................................Pelagohydra(not in European fauna)
Margelopsis Hartlaub, 1897
TYPE SPECIES:Margelopsis haeckelii Hartlaub, 1897 by monotypy.
DIAGNOSIS:Hydroid with hydrocaulus rudiment, without parenchymatic spe-
cializations of the gastrodermis; tentacles indistinctly moniliform; oral tentacles in one
whorl, aboral ones in two to three whorls, medusae buds above aboral tentacles.
Medusa with four perradial tentacular bulbs on bell margin, each with two to six
solid tentacles.
REMARKS:There are two species of Margelopsis in the European fauna, name-
ly Margelopsis haeckelii and M. hartlaubii.See the diagnoses for ways to distinguish
them.
Margelopsis haeckelii Hartlaub, 1897 Figs 12-13
Margelopsis Haeckelii Hartlaub, 1897: 482, pl. 16b figs 12-18; Hartlaub, 1899: 219, figs 1-3
[hydroid].
Margelopsis haeckeli – Hartlaub, 1907: 89, 91, figs 84-86; Müller, 1908: 43, pl. 4 figs 12-17, pl.
5figs 18-19; Mayer, 1910: 80, fig. 38; Leloup, 1930: 97, fig.; Kramp, 1930: 12; Kramp,
1937: 32, fig. 10; Thiel, 1938: 294; Leloup, 1946: 1; Russell, 1953: 95, figs. 41A-C,
P.SCHUCHERT
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42A-B; Werner, 1954: 124, figs 1-9; Werner, 1955: 1-30, figs 1-9; Prévot, 1959: 104, pl.
3 fig. 11; Kramp, 1959: 92, fig. 47; Kramp, 1961: 49; Russell, 1970: 234; Bouillon, 1974:
143.
MATERIAL EXAMINED:BMNH 1967.5.25.1-8, Helgoland, 12 May to 24 July 1958,
medusae and polyps. – BMNH 1967.5.25.6, 2 medusae from Sylt, 10 July 1958, with resting
eggs. – Zoological Museum Hamburg, about 50 mature medusae, collected in plankton by
B. Werner, 24 July 1958, with subitaneous and resting eggs. – Zoological Museum Hamburg,
several polyps from List, collected 27 June 1961, cultivated by B. Werner, with medusae buds.
DIAGNOSIS:Margelopsis polyp with vasiform body,stalk rudiment, two well-
separated sets of tentacles, medusae buds in one whorl oralward of aboral tentacles.
Medusae of up to 2 mm high, umbrella bell-shaped, moderately thick, apical canal
present, 3-6 tentacles per bulb, manubrium base with large vacuolated cells, usually
only females present, eggs of two types: subitaneous eggs developing directly into
polyp stage, diapausing eggs developing first into encysted resting stage.
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 12
Margelopsis haeckelii Hartlaub, 1897; schematic pictures derived from various preserved sam-
ples. Mature medusa with subitaneous eggs and one young polyp, scale bar 0.3 mm. B) Oral
view of a medusa, tentacles clipped, same scale as A.

DESCRIPTION (after examined material and literature): Newly released polyps
actinula-like, ovoid, with short tentacles, tentacles numbers slightly lower than in ful-
ly mature animals.
Mature polyp planktonic, body vase-shaped, resembling a detached tubularian
hydranth, at aboral end a short stalk rudiment with a central depression. Tentacles in
two well-separated sets, rather stiff, with nematocysts concentrated in rings and a small
terminal knob, base of tentacles free of nematocysts. Aboral tentacles slightly longer
than oral ones, 12-15 in two closely approximated whorls, alternately pointing
obliquely up- and downward. Oral tentacles around short conical hypostome, five to
eight in number. Medusae buds borne on body of hydranth just oralward of the aboral
tentacles, sometimes groups of medusa buds on a short stalk. Medusae develop without
envelope, the tentacles are free and not tucked into the subumbrella as in most other
hydromedusae.
Umbrella of very young medusae relatively wider than in adult, apical jelly thin,
nematocysts evenly scattered over exumbrella; broad umbilical canal, stomach length
less than half the height of subumbrellar cavity, a circle of nematocysts surrounds the
mouth-opening, without gonads. Four radial canals and ring-canal narrow. Four
perradial marginal bulbs each with two to three tentacles. Tentacles covered with
scattered clusters of nematocysts, but base of tentacles without nematocysts. Umbilical
canal and marginal bulbs with black pigment. Umbrella becomes higher with further
P.SCHUCHERT
358
FIG. 13
Margelopsis haeckelii Hartlaub, 1897; schematic picture derived from various preserved sam-
ples. Polyp with medusae buds, oral side above, scale bar 0.2 mm.

growth. In a specimen 1.5 mm high, apical jelly considerably thicker than sides of
umbrella, many exumbrellar nematocysts, umbilical canal has narrowed, stomach
considerably longer. Upper third of stomach without gonads, with large gastrodermal
cells covered by thin layer of epidermis. Gonad covering lower two- thirds of the
stomach thin. Three to four tentacles irregularly placed on each marginal bulb, with
irregularly scattered nematocysts which appear as ring-like bands when tentacle
contracted. Upper basal third of stomach clear and transparent in contrast to opaque
brownish grey appearance of lower part.
Adult medusa with bell-shaped umbrella, slightly higher than wide, without
apical process or with small apical process; with scattered exumbrellar nematocysts;
jelly moderately thick, thicker at apex, velum moderately broad to narrow. Stomach
cylindrical, length 2/3 to 1/1 of subumbrellar height; basal portion with large trans-
parent gastrodermal cells; apical canal regularly present (rest of umbilical canal);
mouth simple, circular, margin armed with nematocysts. Four radial canals and ring
canal narrow. Gonad surrounding stomach, leaving upper third free. Eggs amoeboid,
embryos developing attached to manubrium on pedicel, depending on season either
into young polyp or encysted resting stage. Four perradial rounded marginal bulbs,
each with four to seven somewhat stifftentacles, usually irregularly radiating, with
nematocysts concentrated in rings and a small terminal knob, thus nearly moniliform,
gastrodermal cells chordoid. No ocelli. Colour of stomach dark grey with dark brown
pigment granules; marginal bulbs brown. Nematocysts desmonemes, basitrichous
haplonemes, microbasic euryteles, stenoteles.
DIMENSIONS:Adult medusa up to 2 mm high, subitaneous egg production starts
at a bell diameter of 1-1.5 mm and with 3-5 tentacles per bulb, resting eggs are
produced by full sized animals only; subitaneous eggs 0.12-0.13 mm, resting eggs
0.18-0.21 mm; newly released medusa 0.5 mm; newly released polyp resulting from
subitaneous eggs 0.3-0.4 mm, adult polyps 1-2 mm (Werner, 1954), aboral tentacles as
long as hydranth or slightly longer.
BIOLOGY:Polyps and medusae are usually present in the plankton from June to
September,but they have also been seen earlier. They are thought to remain floating
through water currents, as they sink in still water. Their numbers fluctuate drastically
from year to year. Werner (1954, 1955) made detailed investigations on the life histo-
ry and development of this species. Male medusae appear to be extremely rare; Werner
(1954) observed only one hermaphrodite in 250 medusae, the others being all female.
The immature eggs are amoeboid and grow by engulfing other eggs (Müller, 1908).
The eggs develop parthenogenetically (Werner, 1956). Two different types of eggs are
produced: smaller subitaneous eggs and larger resting eggs. Both egg types start their
development attached to the manubrium by a small stalk. The total production of subi-
taneous eggs depends on the food availablity of the medusa and varies in number from
afew eggs to 30 or 40. For the most part, only two to three egg cells mature and emerge
at the same time. Often a medusa bears 20-30 eggs and embryos on the manubrium, of
different ages and different developmental stages. The subitaneous eggs are produced
earlier when water temperatures are between 7 and 15°C. They develop directly within
four to ten days into a small polyp that is then released from the medusa. Later in the
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

year, when water temperatures exceed 15°C, the production of subitaneous eggs stops
and resting eggs are produced. These are larger than the subitaneous eggs and possess
nematocysts on their surface. Generally, only one or two of this type are formed at the
same time and usually not more than six of them remain attached to the manubrium.
The initial development takes place when the egg is attached to the manubrium and
reaches a 'stereo-blastula' stage (a thin layer of ectodermal cells surrounds a mass of
yolky endodermal cells). At this stage development stops, the egg detaches and sinks
to the bottom, where it may attach or not as a lens-shaped cyst. The nematocyst layer
helps in the attachment process. The embryo forms a periderm capsule with a charac-
teristic polygonal pattern. The animal overwinters then as a cyst and after 6-9 months
asmall polyp hatches in the next spring (Werner, 1984). The newly released polyp lives
in the plankton where it grows to full size and then produces medusae.
It seems that only few resting stages survive the winter,as initially there are
only very few hydroids in the plankton. However, through the following medusa pro-
duction and the polyps resulting from their subitaneous eggs, the population density
can grow very rapidly (Werner, 1955).
DISTRIBUTION:Southern North Sea and Irish Sea. Helgoland (Hartlaub, 1897;
1899; Werner, 1955); Norfolk coast (Hamond, 1964), Solway Firth (Russell, 1970),
Weser, Elbe, and Ems Estuary (Kühl, 1962, 1967; 1971), Belgium (Kramp, 1930;
Leloup, 1947). Type locality: Helgoland.
ADDITIONAL DATA:The medusae swim very energetically and jerkily. The short
marginal tentacles are held out rather stiffly (Hartlaub, 1907).
Hartlaub (1907) observed that the polyps normally do not swim actively and
sink slowly to the bottom of the vessel. When sinking, the aboral pole is on top. The
polyps are very sensitive to temperature fluctuations. These observations could not en-
tirely be confirmed by Werner (1955), who observed that the polyps do not regularly
sink with the oral pole downward, and he thinks that the polyp in the free water does
not necessarily orient itself with the aboral pole uppermost.
The aboral stalk rudiment of the polyp has a depression lined with a high
epithelium with cylindrical cells, which Hartlaub (1899) considered reminiscent of the
pneumatophore of the Physophorae. Margelopsis haeckelii has been seen as a model
representing an intermediate stage in the evolution of the Siphonophorae (Totton,
1965). This view was contested by Werner (1955), who observed that this organ is used
by the hydroid to attach itself temporarily,acting like a sucker organ. The cells of the
depression secrete a mucus that is often infested with detritus particles. The aboral
stalk rudiment is thus clearly homologous to the corresponding organ by which the
tubularian actinula larva attaches itself, and ultimately also the stalk of the mature
hydranth.
When the medusa switches from the production of subitaneous- to resting eggs,
there may be a period when there are no conspicuous eggs on the manubrium. Such
medusae can easily be mistaken for mature males, although they do not have any
spermatids (Werner, 1955).
Prévot (1959) depicts a longitudinal section of the polyp. The stalk carrying the
medusae buds (blastostyle) is hollow and communicates with the stomach. In the polyp
material examined for this study, one bifid oral tentacle was seen.
P.SCHUCHERT
360

REMARKS:The original spelling in Hartlaub (1897) is Margelopsis haeckelii,
which must be retained, despite that Hartlaub (1907) used haeckeli,aspelling then
used by all subsequent authors (the specific epithet haeckelii is the genitive form of the
latinized name Haeckelius).
In his study on medusae of Charleston Harbor, McCrady (1859) also described
Nemopsis gibbesii.His description was mainly based on a series of medusae that are
clearly referable to the genus Nemopsis (Bougainvilliidae). But McCrady also found a
polyp in the plankton which he erroneously associated with this medusa. The polyp
closely resembles the polyp of Margelopsis haeckelii,only differing in the medusae
buds that are dispersed between the two whorls of tentacles. McCrady (1859: figs 4-6)
also describes and depicts young medusae stages released by this polyp. As A. Agassiz
(1862) and Hartlaub (1899) have already pointed out, McCrady’s medusae from the
plankton (McCrady, 1859: figs 1-3) were actually Nemopsis bachei L. Agassiz, 1849.
Therefore, Hartlaub (1899) restricted the name Margelopsis gibbesii to the polyp
described by McCrady. Although the first revisor was A. Agassiz (1862) who
synonymized the name N. gibbesii with N. bachei,Hartlaub’sproposal was followed
by Mayer (1910) when he attributed some Margelopsis medusae from North Carolina
to M. gibbesii.McCrady’sdescription did not include mature medusae and the allo-
cation of Mayer appears unfounded, but there is a reasonably good chance that Mayer’s
identifications were correct, as there are no other Margelopsis medusae known from
the region.
Thiel (1938) found a Margelopsis medusa in the Southern Ocean, which he
assigned to M. gibbesii and he claimed that M. gibbesii, M. haeckelii and M. hartlaubii
are conspecific, a possibility already suggested by Mayer (1910: 80). However,this has
not gained acceptance and Kramp (1959) distinguished the medusae of Margelopsis
gibbesii from M. haeckelii by the presence of an apical canal, the thicker jelly and the
viviparity in the latter species. The scattered medusae buds in the polyp of M. gibbesii
can also be added. According to Mayer (1910), Margelopsis gibbesii produces male
medusae, which indicates that both species differ perhaps also significantly in their
life-histories. However,as Werner (1955) cautioned, female medusae that switch from
the production of subitaneous- to resting eggs can easily be mistaken for males. More
biological details on M. gibbesii must be known before both species can be compared
and meanwhile it seems appropriate to keep M. gibbesii separate from M. haeckelii.
Besides M. haeckelii,there is also another Margelopsis species occurring in the
European fauna, namely M. hartlaubii.The latter species is known only from the
medusa phase occurring in deep waters of Norway, thus contrasting with M. haeckelii
which is a shallow water species. Margelopsis hartlaubii can be distinguished by its
lower tentacle number (2-3 per bulb placed beside each other), the thicker jelly,the ab-
sence of an apical canal, and the brick-red manubrium.
Margelopsis hartlaubii Browne, 1903 Fig. 14
Margelopsis hartlaubii Browne, 1903: 10, pl. 1 fig. 2, pl. 3 fig. 3; Mayer, 1910: 82, fig. 40;
Kramp & Damas, 1925: 252, fig. 4; Kramp, 1959: 91, fig. 49; Kramp 1961: 50.
MATERIAL EXAMINED:Zoological Museum Bergen, No 36451, 15 July 1925, Haggernes,
Herdlafjord, 200-400 m, 2 medusae, damaged before fixation. – Zoological Museum Bergen, No
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

26825, Herlöfjord, September 1908 (sic), 1 medusa, fertile female, depicted in by Kramp &
Damas (1925). – Zoological Museum Bergen, No 26826, ca. 300 m, September 1908, 2 medusae
in bad condition, identified by Kramp & Damas (1925).
DIAGNOSIS:Margelopsis medusa measuring 2-4 mm, umbrella spherical to bell-
shaped, jelly relatively thick, no apical canal, with two to three moniliform tentacles
per bulb, gonads much bulging, likely no brooding of eggs.
DESCRIPTION (after Kramp & Damas, 1925): Polyp stage unknown. Medusa
umbrella spherical, 3-4 mm for mature animals, exumbrella with scattered nemato-
cysts. Mesogloea thick, especially at apex, its consistency very soft. The voluminous
manubrium takes up a large part of the subumbrellar cavity,its base quadrangular and
not covered by gonad; gonad occupies the middle region, shaped like a cube or barrel;
oral portion of manubrium conical to cylindrical and mouth margin provided with ring
of nematocysts. Four radial canals are narrow and transparent. Four tentacular bulbs
thick, triangular,without ocelli, with two or three tentacles with a nematocyst-free
base, while the distal region is beaded and end with a terminal knob. Velum broad.
Mesogloea and the radial canals perfectly transparent and uncoloured. Stomach,
marginal bulbs, and tentacular nematocyst clusters contain a brick-red pigment
(observed in living animals).
P.SCHUCHERT
362
FIG.14
Margelopsis hartlaubii Browne, 1903. A) Redrawn from Browne, scale bar 1 mm (1903). B)
Modified after Kramp & Damas (1925).

OWN OBSERVATIONS:Basal, gonad-free region of the manubrium very short;
large vacuolated cells could not be seen in the examined preserved material; top of the
manubrium is flat, apical canal thus absent; gonad covers most of the manubrium and
leaves only short regions uncovered at both ends. Gonad encircles the manubrium
without interruption. Tentacle bulbs prominent, their epidermal portion bulging, a
gastrodermal chamber present. One sample (26825) mature or almost mature female,
numerous eggs are clearly visible within gonad, but no eggs or embryos attached to
manubrium as in M. haeckelii.Some mature medusae could be mature males. Tentacles
distinctly moniliform, apparently quite short, usually two per bulb. Tentacles contain
only desmonemes and microbasic mastigophores, stenoteles not observed; small
stenoteles seem to be present around mouth opening. Undischarged desmonemes (ca.
15x 10 µm) have a thread with characteristic rope structure. Mastigophores have a
spherical capsule of about 10 µm diameter.
BIOLOGY:Occurs in 200-400 m depth, recorded from April to September, but
only few records are available.
DISTRIBUTION:Norwegian fjords. No type locality was specified, the original
material came from Osterfjord and Herløfjord, 0-400 m.
REMARKS:Margelopsis hartlaubii Browne, 1903 is a very rare medusa, known
only from a few specimens. Its polyp stage is unknown. The species has been syno-
nymized with Margelopsis gibbesii and M. hartlaubii by Thiel (1938), a proposal that
has not gained acceptance (see remarks under M. haeckelii). It is actually quite distinct
from M. haeckelii:about two times larger,it has a thick mesogloea, it has only two to
three tentacles per bulb, and there is no apical canal. Furthermore, the available
material suggests that there is no brooding in this species and males may exist.
Nevertheless, more data on this species are needed, e.g. detailed nematocyst
data and information on its polyp stage should be obtained in order to confirm the
taxonomic position of this species.
FAMILY PENNARIIDAE MCCRADY, 1859
SYNONYM:Halocordylidae Stechow, 1921.
DIAGNOSIS:Hydroid colony pinnate, occasionally bushy,stem monosiphonic,
giving rise alternately from opposite sides to two series of hydrocladia; hydrocaulus
and hydrocladia with terminal hydranths (monopodial); hydranths on short pedicels on
upper side of the hydrocladia; hydranths pear-shaped; tentacles of two types: in distal
half of hydranth more or less capitate tentacles in one oral whorl and more in indistinct
whorls below,on lower part of hydranth one aboral whorl of semifiliform to slightly
capitate aboral tentacles; gonophores developing above aboral tentacles, eumedusoids,
liberated or not.
Medusa a simple eumedusoid; manubrium not extending beyond umbrella mar-
gin; gonads completely surrounding manubrium; four radial canals; four permanently
rudimentary tentacles, usually reduced to mere bulbs, without ocelli.
REMARKS:The family contains only the genus Pennaria Goldfuss, 1820.
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

Genus Pennaria Goldfuss, 1820
TYPE SPECIES:Pennaria disticha Goldfuss, 1820.
SYNONYMS:Globiceps Ayres, 1854; Eucoryne Leidy, 1855; Halocordyle Allman, 1872.
DIAGNOSIS:With the characteristics of the family.
REMARKS:There are several medusa-based species (Kramp 1959, 1968). They
are mostly indeterminate and some of them do not belong to the genus Pennaria at all
(Petersen, 1990). For the synonymy and validity of the name Pennaria see Calder
(1988) and Gibbons & Ryland (1989). Only Pennaria disticha is relevant for the
European fauna.
Pennaria disticha Goldfuss, 1820 Fig. 15
Pennaria disticha Goldfuss, 1820: 89; Mayer, 1910: 24, fig. 1A-E; Brinckmann-Voss, 1970: 40,
text-figs 43, 45-50; Gibbons & Ryland, 1989: 387, fig. 5 [taxonomy]; Schuchert, 1996:
142, fig. 85a-c; Watson, 1999: 16, fig. 10A-I; Bouillon et al.,2004: 103, fig. 55A-C.
Pennaria Cavolinii Ehrenberg, 1834: 297; Allman, 1872: 364, fig 80.
Pennaria cavolini – Weismann, 1883: 121, pl. 17 figs 1-5, pl. 18.
Halocordyle disticha – Rees & Thursfield, 1965: 4; Millard, 1975: 41, figs 16C-G; Hirohito,
1977: 2, fig. 1, pls 1-3; Garcia-Corrales & Aguirre, 1985: 85, figs 1-3 [synonymy]; Morri
&Boero, 1986: 31, fig. 11; Wedler & Larson, 1986: 73, fig. 4C; Calder, 1988: 57, figs
43-45 [complete synonymy]; Hirohito, 1988: 28, figs 9a-d, pl. 1 fig. C; Östman et al.,
1991: 607, figs 1-18; da Silveira & Migotto, 1991: 437, fig. 1.
MATERIAL EXAMINED:MHNG INVE29809, Mallorca, Cala Murada, coll. P. Schuchert 24
August, 2000 fertile, depth 1 m, 16S sequence AM088481, 18S sequence AY920762. – MHNG
INVE 36918, Naples, coll. 1892, few hydranths left. – MHNG INVE 36919, Naples, coll. 1900,
fertile. – MHNG INVE 36920, origin unknown, likely Mediterranean, fertile. – MHNG INVE
35468, USA, North Carolina, Morehead City, marine anchorage, fertile, collected 7 October
2000 by Dr Alberto Lindner. – BMNH 1964.8.7.5 Pennaria tiarella,slide preparation, Woods
Hole, Mass. USA, fertile, hydrocladia bearing a single hydranth, stenoteles max. 25 µm, thus
larger than in Weill (1934) and within the range observed for P.disticha (Hirohito, 1977). –
Honduras, Utila, Blue Bayou Beach, coll. F. Sinniger 13 February 2004, depth 1 m, hydranths
more delicate than European forms. – Thailand, Andaman Sea, Koh Phi Phi, Ao Nui, 16 April
2000, 10-20 m, collected by Dr A. Faucci. – New Zealand, Hauraki Gulf, Devonport, 26 July
2002, one medusa from plankton. – See also Schuchert (1996, 2003).
DIAGNOSIS:Feather-like branched hydroid colony (pinnate), firm perisarc,
gonophore medusoid, released or not, with four bulbs, no ocelli.
DESCRIPTION:Hydroid colonies forming branching, feather-like shoots, arising
from thick creeping, ramified stolons. Growth monopodial with hydranths on all ends.
Main axis thick, often curved, monosiphonic, perisarc with smooth stretches and
annulated stretches in more or less regular intervals, regularly so distal to insertion of
hydrocladia (side-branches) and hydranth pedicels. Hydrocladia of one side form an
angle of about 120-140 degrees with those from other side, curved, longest hydrocladia
usually found at about 1/3 to 1/2 stem length (measured from base), hydrocladia are
about half as thick as stem, they either bear hydranths on pedicels (ramuli) or
secondary hydrocladia with hydranths again on pedicels. Pedicels (ramuli) of
hydranths originate on upper side of hydrocladia, all approximately of same length and
evenly spaced, with annulation at their base or throughout, younger ones without annu-
lation. Hydranths spindle- to pear shaped, hypostome dome-shaped. Tentacles of two
types: an aboral whorl of about 12-14 long, filiform to slightly capitate tentacles and
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365
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 15
Pennaria disticha Goldfuss, 1820, after Mediterranean material. A) Colony, modified after
Mayer (1910), actual size. B) Part of branch with two hydranths, one with an almost mature
medusoid, scale bar 0.5 mm. C) Female medusoid that has already spawned some eggs, modi-
fied after García-Corrales & Aguirre (1985), scale bar 0.2 mm.

up to 16 short capitate tentacles distributed in two to three indistinct whorls on distal
half of hydranth. Knobs of capitate tentacles, except of oral ones, can be reduced to
mere nematocyst cap, thus being almost filiform. Nematocysts of aboral tentacles
mainly on aboral side and terminally (= semifiliform according to Petersen, 1990),
aboral epidermis of filiform tentacles about three times thicker than on oral side,
gastrodermal cells chordoid.
Gonophores oblong medusoids arising on short pedicels just above whorl of
long filiform tentacles. Gonads encircling manubrium, four radial canals and circular
canal present, with four marginal bulbs, with small velum, without ocelli, tentacles
normally absent, rarely some rudiments present. Marginal bulbs without a concen-
tration of nematocysts. Colonies gonochoristic, female medusoids with four to six
eggs. Gonophores can be released as short-lived medusoids, or they spawn while still
attached to hydroid.
Nematocysts of polyp: stenoteles of three to four size classes, microbasic
mastigophores with inclusion body, microbasic heteronemes without inclusion body,
basitrichous isorhizas, desmonemes. Medusoids with stenoteles only.
Colour of stem dark brown to black, hydrocladia brown, fading distally to clear.
DIMENSIONS:Fertile colonies usually around 8-15 cm high, but may excep-
tionally reach 40 cm. Hydranths 0.9-1.5 mm high; medusoids 0.7-1.1 mm. More
measurements are given in García-Corrales & Aguirre (1985). Nematocyst sizes can be
found in Millard (1975), Hirohito (1977), García-Corrales & Aguirre (1985), Calder
(1988), da Siveira & Migotto (1991), Östmann et al.(1991), Schuchert (1996), Watson
(1999). Some of these authors also figure them.
BIOLOGY:Occurs usually in shallow waters of a few meters depth along rocky
coasts with some wave action. In the Mediterranean, the colonies are active from
spring to fall, the colonies overwinter as stolons (Brinckmann-Voss, 1970; Morri &
Boero, 1986). In more tropical waters they can also be present all year round.
Spawning is induced by a reduction of the light intensity (sunset) (Baker, 1936;
Brinckmann-Voss, 1970; Calder, 1988; Genzano & Kubota, 2003). The eggs develop
in the open water.
Sometimes, the colony form can vary quite drastically,the normal pinnate form
can intergrade with a more bushy form (da Silveira & Migotto, 1991). Also Calder
(1988) found that the colony form varies depending on wave exposure: colonies from
sheltered places were more gracile, internodes of both branches and stem were long
and slender, branches and ramuli elongate, while specimens from wave-swept ledges
were small and compact, internodes of caulus and branches were thicker and shorter
and the branches and ramuli relatively shunted. However, the annulation did not differ
significantly.
Prey capture and nematocyst function were investigated by e. g. Clark & Cook
(1986); Östman et al.(1991), and Kem & Östman (1992). The feeding biology was
examined by Pardy et al. (1968, as Pennaria tiarella).
This species has been the subject of a considerable number of experimental and
developmental studies (sometimes under the synonym Pennaria cavolinii). Rege-
neration studies have been made by Cerfontaine (1902), Gast & Godeeski (1903),
P.SCHUCHERT
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Brinckmann-Voss (1970), Tardent (1963, 1965). Hydranth development is described
and depicted in Berrill (1952). Gonophore development is documented by Weismann
(1883), Berrill (1952), and García-Corrales & Aguirre (1985). Gametogenesis was
examined by Weismann (1883). Initially, there are many oogonia in female
gonophores, but only a few grow to full size and the others are phagocytosed.
There are many reports on the early development and ultrastructure based on
populations from the USA, either named Halocordyle disticha or Pennaria tiarella
(e. g. Hargitt, 1899, 1900, 1904; Cowden 1964, 1965a, 1965b; Summers & Haynes,
1969; Summers, 1970, 1976; Lesh-Laurie, 1976; Thomas et al.,1987; Martin, 1980,
1987, 1988a, 1988b, 1990, 1991, 1992a, 1992b, 2000; Martin & Archer, 1986a, 1986b,
1997; Martin & Thomas, 1977, 1981a, 1981b, 1983; Hotchkiss et al., 1984; Brumwell
&Martin, 1996).
DISTRIBUTION:Circumglobal in warm temperate to tropical waters. The occur-
rence at the Azores (Cornelius, 1992) and the Strait of Gibraltar (Medel & López-
González, 1996) seem to mark the northern limit for the eastern Atlantic. In the North-
Eastern Atlantic also known from the Cape Verde Islands (Rees & Thursfield, 1965),
Madeira (Wirtz & Debelius, 2003). Widespread in the western Mediterranean (e. g.
Brinckmann-Voss, 1970; García-Corrales & Aguirre, 1985; Bouillon etal.,2004) and
eastern Mediterranean (e. g. Vervoort, 1993). Often recorded from the western Atlantic
(e. g. Vervoort, 1968; Hirohito, 1977; Wedler & Larson, 1986; Calder, 1988; Migotto,
1996). The distribution further includes the Red Sea (Hirohito, 1977; Vervoort, 1993),
Indian Ocean (e. g. Ritchie, 1910; Jarvis, 1922; Stechow, 1925; Mammen, 1963;
Millard & Bouillon, 1973; Millard, 1975; Watson, 1999), Malayan Archipelago (Pictet,
1893; Schuchert, 2003), North-Eastern Pacific(Hargitt, 1927; Hirohito, 1977; 1988);
south-western Pacific(Schuchert, 1996; Watson, 1999), central Pacific(Cooke, 1977;
Gibbons & Ryland, 1989; Kirkendale & Calder, 2003) and western Pacific (Fraser,
1938; 1948; Calder et al., 2003). Type locality: Gulf of Naples, Mediterranean.
REMARKS:Pennaria disticha is a conspicuous animal and quite well known. For
the European fauna, there are no serious taxonomic problems. Its morphological
variability was certainly the main reason for its complicated taxonomic history. The
complete synonymy is not given here, as this has been done by Calder (1988), Hirohito
(1977), García-Corrales & Aguirre (1985), and Gibbons & Ryland (1989).
Most Pennaria species based on the hydroid phase were synonymized with
P. disticha,with the prominent exception of P.wilsoni (Hirohito, 1988; Watson, 1999).
Pennaria tiarella (Ayres, 1854), a species originally described from Long
Island (New York), was already considered to be closely related to P.disticha by Mayer
(1910). Most subsequent authors (e. g. Fraser, 1944), however, kept it separate. Also
Brinckmann-Voss (1970) held it distinct from P.disticha on account of the variable
length of the ramuli. Later authors (see above) included also P. tiarella in the
synonymy of P.disticha.Weill (1937) reported a comparatively small size for the
stenoteles of P. tiarella,but an examination of material from the same locality (BMNH
1964.8.7.5, Woods Hole) did not confirm this and the stenoteles have a maximal size
that lies within the range found in other populations of P. disticha (see Hirohito, 1977).
The embryonic development to the planula larva has been examined in great
detail by American students using animals from the USA (identified as P. tiarella or P.
367
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

disticha). Surprisingly, only few such investigations have been made using
Mediterranean animals and there is an unresolved discrepancy. Cavolini (as cited in
Weismann, 1883) observed that the fertilized eggs become encapsulated and over-
winter as resting stages. This has never been observed again and perhaps Cavolini’s
observations can be attributed to the simple observation tools available at his time.
Whatever, this should be re-investigated.
FAMILY CLADOCORYNIDAE ALLMAN, 1872
DIAGNOSIS:Hydroid colonial, simple stolonal or sparingly branched, hydranth
club-shaped, one whorl of moniliform or capitate oral tentacles, aboral tentacles
moniliform or branched capitate, scattered or in several whorls; with nematocysts on
body wall arranged in conspicuous pads or scattered around the base of oral and aboral
tentacles; gonophores carried singly or on short, branched pedicels on lower or middle
part of hydranth; gonophores developing into free medusae or fixed sporosacs.
Medusa with two opposite perradial tentacles possessing stalked cnidophores,
bell margin with four bulbs, of which two are without tentacles; above each atenta-
culate marginal bulb an exumbrellar pad containing macrobasic euryteles; tentaculate
marginal bulbs large, without nematocyst pads; gonads interradial on manubrium.
REMARKS:The concept and relationships of the family Cladocorynidae are
outlined by Petersen (1990). It comprises the genera Cladocoryne Rotch, 1871 and
Pteroclava Weill, 1931.
KEY TO THE GENERA:
1a polyps with capitate oral tentacles; gonophores are fixed sporosacs . . . . . . Cladocoryne
1b polyp with moniliform oral tentacles; gonophores are free medusae . . . . . . . . . . . . . . . .
........................................Pteroclava (not in European fauna)
Genus Cladocoryne Rotch, 1871
TYPE SPECIES:Cladocoryne floccosa Rotch, 1871 by monotypy.
SYNONYMS:Polycoryne Graeffe, 1883a; Cladocorynopsis Mammen, 1963; Lobocoryne
Mammen, 1963.
DIAGNOSIS:Cladocorynidae with long hydocauli, these unbranched or sparingly
branched, covered by perisarc. Hydranth club-shaped, with oral whorl of capitate
tentacles, one to four whorls of branched-capitate aboral tentacles; on hydranth body
usually nematocyst patches containing macrobasic euryteles; gonophores fixed
sporosacs between or over aboral tentacles.
Cladocoryne floccosa Rotch, 1871 Fig. 16
Cladocoryne floccosa Rotch, 1871: 228; Du Plessis, 1880: 176, pl. 9; Allman, 1872: 380, fig. 82;
Kühn, 1910: 69, fig. D, pl. 6 figs 28-34, pl. 7 figs 35-36; Kühn, 1913: 184, figs 28-36,
pls 6-7; Philbert, 1936: 1, figs 1-8; Weill, 1937: 1, figs 1-5; Brinckmann-Voss, 1970: 69,
figs 80-82; Millard & Bouillon, 1974: 11, fig. 1D-E; Millard, 1975: 65, figs 21A-B;
Bouillon et al., 1987: 297, figs 1 & 5-6; Hirohito, 1988: 52, figs 16 b-f; Migotto, 1996:
17, fig. 4a-b; Schuchert, 1996: 97, fig. 57a-c; Watson, 1999: 11, fig. 7A-D; Peña Cantero
&García Carrascosa, 2002: 46, fig. 9e; Calder et al.,2003: 1178, fig. 3; Bouillon et al.,
2004: 110, fig. 57G.
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369
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 16
Cladocoryne floccosa Rotch, 1871; A-D after preserved material from the Mediterranean; E-F,
after Kühn (1910). A) Hydroid with sporosacs, scale bar 0.5 mm. B) Slightly compressed
microscopic preparation of a hydranth, note position of eurytele clusters (arrows), scale bar 0.2
mm. C) Part of tentacles of aboral set, note chordoid gastrodermis, scale bar 0.1 mm. D)
Macrobasic eurytele, scale bar 40 µm. E) Histological longitudinal section of an almost mature
female sporosac. F) Longitudinal section of a mature male sporosac.

Hydra corynaria Bosc, 1797.
Cladocoryne pelagica Allman, 1876: 255, pl. 10 figs 6-7.
Polycoryne helleri Graeffe, 1883a: 202, pl. figs 1-5; Graeffe, 1883b: 320, synonym.
Cladocoryne simplex Perrier, 1886: 81, fig. 3.
Cladocoryne floccosa var. sargassensis Hargitt, 1909: 369, figs 1-2.
Cladocoryne sargassensis –Kingsley, 1910: 19, fig. 81.
not Cladocoryne floccosa –Rees & Thursfield, 1965: 46 [= C. haddoni Kirkpatrick, 1890].
MATERIAL EXAMINED: Cala Murada, Mallorca, Spain, June 1997, on rock in 0.5-2 m
depth, fertile, examined alive. – MHNG INVE 29808, Cala Murada, Mallorca, 1 m, 13 August
2000, on Peysonnellia,examined alive, infertile. – BMNH 1974.11.21.38, Italy, Naples, 20 April
1967, material of Brinckmann-Voss (1970), not well preserved (maceration by formalin). – MH-
NG INVE 36913 Naples, Cap Misene 23.01.1895, young sporosacs present, on various sub-
strata. – MHNG INVE 36912, Villefranche-sur-Mer, infertile.
DIAGNOSIS:Cladocoryne species with three to four whorls of aboral tentacles,
patches of macrobasic euryteles among oral and aboral tentacles, gonophores without
radial canals, mature females with one to two eggs.
DESCRIPTION (after own material and literature): Hydroid with unbranched stem
or rarely branched once, arising from adhering, ramified stolons. Stems covered by
perisarc, smooth or with annulated stretches and becoming thinner distally to terminate
below hydranth. Hydranth cylindrical to club-shaped, dome-shaped hypostome; with
tentacles of two types in two well-separated sets: a single whorl of four to six short
capitate oral tentacles, and 12-22 aboral tentacles in three to four alternating whorls,
whorls can be indistinct. Aboral tentacles branched, side-branches short and capitate,
in two lateral rows and one median row on upper side; lateral secondary tentacles up
to seven per row, median row with zero to two. All side-branches and end of main
branch with a terminal spherical nematocyst cluster.Sometimes some secondary
tentacles without stalk and reduced to mere nematocyst clusters. Gastrodermis of
tentacles chordoid. Hydranth with nematocyst patches or pads on body wall between
oral tentacles and lowest aboral tentacles. Colours: hydranth light reddish brown, oral
region with conspicuous white pigment.
Gonophores on short pedicels, two to eight borne on the hydranth among or
above the upper aboral tentacles, spherical to oblong, remaining fixed as sporosacs
without radial canals or circular canal (cryptomedusoid type), females usually with one
egg only,colour white.
Nematocysts: stenoteles and macrobasic euryteles.
DIMENSIONS:Colony height a few mm to 12 mm; caulus diameter 0.15 mm;
hydranth height 1-1.2 mm, diameter 0.3 mm; length aboral tentacles tentacle 0.7-
1.3 mm; sporosac size: 0.3-0.4 mm. Nematocyst sizes are given in Philbert (1936);
Weill (1937); Millard & Bouillon (1974); Millard (1975); Migotto (1996); Schuchert
(1996); Watson (1999).
BIOLOGY:Cladocoryne floccosa has been reported from depths ranging from 0
to 50 m. It has often been observed on Sargassum weeds, but also occurs on many other
solid substrata like algae, hydroids, sponges, and rocks. In the Mediterranean, it can be
found from January to autumn, fertile colonies have been observed in January and from
end of April to July (Brinckmann-Voss, 1970; Boero & Fresi, 1986; own
observations).
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ADDITIONAL DATA:Fertile animals often reduce their tentacles, sometimes
leading to tentacle-less hydranths (reproductive exhaustion). Kühn (1910) describes
the formation of the gonophores and the gametogenesis. The mature female sporosacs
usually contain one egg only. Initially there are many eggs, but during the maturation
one of them phagocytoses all the others. The embryonic development takes place in the
sporosac. Philbert (1936) depicts the metamorphosis of the larva to the primary polyp.
The nematocysts are depicted in Weill (1937). A longitudinal section of a hydranth is
depicted Prévot (1959) and in Bouillon et al. (1987, fertile hydranth). Peña Cantero &
García Carrascosa (2002) found branched stems that had up to four hydranths.
DISTRIBUTION:Circumglobal in temperate to tropical waters. Along the
European coasts known from north-west of Ireland (Allman, 1876, as C. pelagica), the
English Channel (Rotch, 1871; Philbert, 1936; Teissier, 1965), the Iberian Peninsula
(Da Cunha, 1944; Medel & López-González, 1996), western Mediterranean (Du
Plessis, 1880; Motz-Kossowska, 1905; Brinckmann-Voss, 1970; Peña Cantero &
García Carrascosa, 2002; and more), eastern Mediterranean (Picard, 1958; Morri &
Bianchi, 1999). Also known from the western Atlantic (Hargitt, 1909 as Cladocoryne
floccosa var. sargassensis;Migotto, 1996); the Indian Ocean (Millard & Bouillon,
1974; Watson, 1999); the western Pacific (Hirohito, 1988; Schuchert, 1996); the
eastern Pacific(Lees, 1968; Calder etal., 2003). Type locality: on stones at low tide at
Herm, Guernsey, Channel Islands, United Kingdom.
REMARKS:This is a characteristic species that cannot be confounded with any
other hydroids of the European fauna. The synonymy is quite well established.
Polycoryne helleri Graeffe, 1883a was recognized as a synonym by Graeffe (1883b)
himself. Cladocoryne pelagica Allman, 1876 was described based on a fertile colony
found on floating Sargassum seaweed northwest of Ireland. Allman kept it distinct on
account of its smaller size and the annulated base of the pedicel. These traits are no
longer considered diagnostic and in his revision, Philbert (1936) regarded it as a syn-
onym of C. floccosa,likewise also C. simplex Perrier, 1886, and C. haddoni
Kirkpatrick, 1890. Most subsequent authors took up Philbert's conclusion, but Bouillon
et al. (1987) re-described C. haddoni based on material from Papua New Guinea and
found sufficient differences to C. floccosa to permit a reliable identification, even of
immature specimens. Cladocoryne haddoni was therefore recognized as a distinct
species. Cladocoryne pelagica, C. simplex and C. sargassensis are very likely conspe-
cificwith C. floccosa,although the original descriptions are usually not detailed
enough. A re-examination of the type material of C. pelagica and a detailed exami-
nation of Cladocoryne hydroids on Sargassum would therefore be helpful. Calder et al.
(2003) discovered another likely synonym of C. floccosa,namely Hydra corynaria
Bosc, 1797, a Cladocoryne species that was also originally described based on material
growing on Sargassum.Because Bosc's name has not been used since its original
description Calder et al. (2003), based on provisions of the ICZN, invalidated Bosc's
name and to declared Cladocoryne floccosa Rotch, 1871 a protected name.
FAMILYCLADONEMATIDAE GEGENBAUR, 1856
SYNONYMS:Cladonemiden Gegenbaur, 1856; emended to Cladonematidae by Poche
(1914: 70); Stauriidae Hincks, 1868; Dendronemidae Haeckel, 1879; Eleutheriidae Stechow,
1923.
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

REFERENCES:Günther (1903), Hartlaub (1887), Stechow (1923), Bouillon (1985), Calder
(1988), Petersen (1990), Bouillon & Boero (2000).
DIAGNOSIS:Hydroid colony stolonal or rarely sparingly branched, arising from
creeping stolons. Hydranth spindle-shaped, one whorl of four to ten solid oral capitate
tentacles, with or without aboral whorl of filiform tentacles; mouth opening into a pre-
oral chamber formed by epidermal gland cells; medusa buds not enclosed in periderm
film, carried singly or in clusters at base of hydranth or above filiform tentacles if they
are present.
Medusa adapted to benthic mode of life, some species still able to swim freely;
with or without a thickened continuous or broken ring of nematocysts around umbrel-
lar margin, with or without brood-chamber above manubrium; manubrium cylindrical,
with or without protruding pouches; mouth either simple, or with oral nematocyst
clusters, or with ramified oral tentacles; gonads either completely surrounding manu-
brium, or on manubrial pouches, or in special brood-chamber above manubrium, in
latter case also sometimes additionally in subumbrellar epidermis; number of radial
canals variable but usually more than four, some may be branched, final number of
canals entering circular canal usually corresponding or slightly exceeding the number
of marginal tentacles; marginal tentacles hollow, branched, with branches bearing
nematocyst clusters and branches having adhesive organs; with abaxial ocelli on
tentacle base.
REMARKS:As some Cladonematidae can be cultivated quite easily, they have
become the subject of numerous developmental and molecular studies. They thus
became quite well known even to non-specialists. The European Cladonematidae
species present few taxonomic problems and the species are mostly well known,
though the genus Dendronema remains problematic. However, taxonomic problems
persist at the genus level.
The family Cladonematidae has been kept separate from the Eleutheriidae
Stechow, 1923 by a number of authors (for more details see Calder, 1988). The latter
family comprised the genera Staurocladia and Eleutheria.The separation of both
families is ambiguous and not necessary and the proposal of Petersen (1990) to unite
them is here also adopted. A good example in favour of this is Staurocladia portmanni
Brinckmann, 1964, which is perfectly intermediate between Staurocladia and
Cladonema,differing basically only in the branching of the tentacles. The genera
Cladonema, Staurocladia, and Eleutheria are linked by a number of synapomorphic
characters, such as the preoral chamber in the hydroid, the branched medusa tentacles
with adhesive ends, and the number of radial canals (Petersen, 1990).
In current usage (Kramp, 1961; Bouillon, 1985; Bouillon & Boero, 2000), the
family comprises four genera: Cladonema,Dendronema, Staurocladia, and Eleutheria.
Dendronema is somewhat problematic and the distinction of the three remaining
genera relies principally only on the morphology of the capitate tentacles of the
medusa. Cladonema has tentacles that are branched more than once and its umbrella is
not reduced. In Staurocladia, the tentacles are only bifid and the upper branch bears
additional nematocyst clusters besides the terminal one. Eleutheria was diagnosed as
having bifidtentacles with a single terminal nematocyst cluster,and additionally a
P.SCHUCHERT
372

brood-chamber above the manubrium. There remain, however, problems with this clas-
sification, especially so for the scope of Staurocladia.
Hartlaub (1917) established the genus Staurocladia solely to separate
Eleutheria vallentini,E. claparedii, and others from Eleutheria dichotoma.He found
this necessary to account for some of the peculiarities of E.dichotoma:the brood-
chamber, the hermaphroditism, and the gonostyle in the polyp phase. Hartlaub there-
fore used the combination Staurocladia claparedii (Hartlaub, 1889),as this species has
no brood-chamber (Müller, 1911; Lengerich, 1923a). Lengerich (1923a) used only a
single genus, Eleutheria,for all Cladonematidae. Although this would resolve the
problem of paraphyletic genera, it creates unwanted name changes for widely known
species. Probably unaware of Hartlaub’s publication, Gilchrist (1919) had similar
thoughts and suggested the genus name Cnidonema for the Eleutheria species of the
southern hemisphere. He also thought that it might be necessary to introduce a new
genus for E. claparedii if this species should have no brood-chamber. Browne &
Kramp (1939) and Kramp (1959, 1961, 1968) took up Hartlaub’sdiagnosis, but
modified the definition so that Staurocladia was differentiated from Eleutheria by the
number of nematocyst clusters per tentacle (Eleutheria one, Staurocladia more than
one) and the absence or presence of a brood-chamber.Browne & Kramp (1939) placed
E.claparedii in the genus Eleutheria,because they were probably unaware that it has
no brood-chamber. Brinckmann-Voss (1970) became aware of this discrepancy and
changed the genus diagnosis of Eleutheria accordingly to "with or without brood-
chamber above manubrium". The genera Staurocladia and Eleutheria were hence
distinguished only on account of the number of nematocyst clusters. However, later
authors reverted to Kramp's (1961) diagnosis (e. g. Bouillon, 1985; Petersen, 1990;
Bouillon & Boero, 2000), but were inconsistent in placing E. claparedii in the genus
Eleutheria.
Distinguishing a genus solely on the number of tentacular nematocyst clusters
appears quite ambiguous and very prone to give polyphyletic assemblages. It is thus
quite unlikely that the present genera correspond to a monophyletic groups.
Unfortunately,there are few useful characters for a phylogenetic analysis of the
members of the Cladonematidae. Synapomorphies that can be used to find species
groupings are given in table 1. There are more apomorphies, but either they are
autapomorphies (gonostyle, very extensible hydranth, brood-chamber,centripetal
canals, radial canals with processes, apical cavity), or only examined for one or few
species (desmonemes in polyp stage, heteronemes in polyp stage). Some characters are
not really usable (lateral or aboral position of nematocyst clusters).
Using these characters for a cladistic analysis of representative members of the
family was not very helpful (table 1, figure 17). There are several unresolved poly-
tomies, but it is worth mentioning that Staurocladia is evidently a polyphyletic group.
In this case, it seems nevertheless prudent not to use these results to redefine the gen-
era because taxonomic stability should be given more value than a classification based
on a poorly resolved cladogram. Perhaps a thorough molecular analysis can provide the
necessary data, but until then, the diagnoses for Eleutheria and Staurocladia as given
in Brinckmann-Voss (1970) should be used.
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

P.SCHUCHERT
374
TABLE 1
Characters used in the phylogenetic analysis of the genera of the Cladonematidae
Species / Characters 1 2 3 4 5 6 7 8 9 10 11 12 13
Dipurena reesi Vannucci, 1956 1 0 0 0 0 0 0 0 0 0 1 0 0
Dipurena strangulata McCrady, 1859 1 0 0 0 0 0 0 0 0 0 0 0 0
Cladosarsia minima Bouillon, 1978 ? ? 0 0 0 0 0 0 0 1 1 0 0
Cladonema radiatum Dujardin, 1843 1 1 0 1 1 1 1 1 0 1 1 0 0
Dendronema stylodendron Haeckel, 1879 ? ? 0 1 1 1 1 1 0 1 1 0 0
Eleutheria dichotoma Quatrefages, 1842 1 1 1 1 1 0 0 0 1 0 0 1 1
Eleutheria claparedii Hartlaub, 1889 0 ? 1 1 1 0 0 0 1 0 0 0 1
Staurocladia portmanni Brinckmann, 1964 1 1 0 1 1 1 1 1 0 0 1 0 0
Staurocladia vallentini (Browne, 1902) 1 1 1 1 1 0 0 0 1 0 1 1 1
Staurocladia wellingtoni Schuchert, 1996 0 1 1 1 1 1 1 1 0 0 1 0 0
characters:
1polyp: filiform tentacles: none (0), present (1)
2polyp: gonophore without perisarc film (1)
3mesogloea rigid, medusa thus able to swim freely (0), not so (1)
4medusa tentacles with adhesive ends; absent (0), present (1)
5four radial canals (0), more than four (1)
6radial canals unbranched (0), branched (1)
7oral knobs absent (0), present (1)
8manubrial pouches absent (0), present (1)
9medusae budding absent (0), present (1)
10 tentacles branched more than once, no (0), yes (1)
11 medusa one terminal nematocyst cluster per tentacle only (0), additional clusters present (1)
12 continuous marginal nematocyst ring absent (0), present (1)
13 tentacles and radial canals in phase (0), out of phase (1)
note: the character "preoral chamber", likely an apomorphy for the Cladonematidae, was not used, because its state is known for three species only
(C. radiatum,S. portmannii,E. dichotoma)

KEY TO THE CLADONEMATIDAE:
1a medusa tentacles branched more than once . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1b medusa tentacles branched once . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2a oral nematocyst knobs of medusa simple . . . . . . . . . . . . . . . . . . . . . . . . . . . Cladonema
2b oral nematocyst knobs of medusa branched . . . . . . . . . . . . . . . . . . . . . . . . Dendronema
3a medusa tentacles with a single nematocyst knob . . . . . . . . . . . . . . . . . . . . . . Eleutheria
3b medusa tentacles with a several nematocyst knobs . . . . . . . . . . . . . . . . . . . Staurocladia
Genus Cladonema Dujardin, 1843
TYPE SPECIES:Cladonema radiatum Dujardin, 1843 by monotypy.
SYNONYMS:Stauridia Forbes, 1848; Stauridium Krohn, 1853b.
REFERENCES:Kramp (1961); Bouillon (1985); Calder (1988); Petersen (1990); Bouillon
&Boero (2000).
DIAGNOSIS:Hydroid mostly stolonal, occasionally branched, one oral whorl of
four to five capitate tentacles, with or without filiform tentacles, medusa buds borne
singly on hydranth body immediately above filiform tentacles or in similar position
when these are absent. Medusae adapted for swimming and adhering to surfaces, with
bell-shaped umbrella; manubrium cylindrical, in adults with pouches, gonads without
perradial separations, mouth short, unbranched lips bearing four to six spherical
nematocyst clusters; without apical chamber above manubrium; radial canals bifur-
cated or simple, final number of canals entering circular canal usually of same number
375
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG.17
Genera of the Cladonematidae: Phylogenetic analysis of morphological characters using
maximum parsimony: Strict consensus tree of the 17 trees with minimal length (18 steps,
HI=0.28, CI=0.72, RI=0.81). The consensus tree of the bootstrap analysis was identical, the
percentage of node support is given in boxes. Some selected synapomorphies are also given
(numbers along branches, see table 1).

as marginal tentacles; marginal tentacles branching, each with one to six proximal
branches ending in an adhesive organ and one to ten more distal branches with nema-
tocyst clusters; abaxial ocelli with lens.
Cladonema radiatum Dujardin, 1843 Fig. 18
Cladonema radiatum Dujardin, 1843: 1134; Dujardin, 1845: 271, pl. 14 figs C1-C7, pl. 15 figs
C8-C19; Krohn, 1853b: 420, pl. 13; Keferstein & Ehlers, 1861: 85, pl. 13 fig. 5; Van
Beneden, 1867: 139, pl. 12; Hincks, 1868: 62, text fig. 5, pl. 11; Allman, 1871-1872: 216,
pl. 17; Hincks, 1872: 391, pl. 21, fig. 6; Hartlaub, 1887: 266, 651; Billard, 1905: 500;
Hartlaub, 1907: 132, figs 123-126; Müller, 1908: 30, pl. 3 figs 1-2; Mayer, 1910: 99, figs
53-55; Lengerich, 1923a: 331, figs A-S; Weill, 1937: 443, fig. 1; Russell, 1953: 105, figs
49-51; Kramp, 1959: 96, fig. 55; Brinckmann & Petersen, 1960: 388, fig. 2; Kramp,
1961: 57; Kramp, 1968: 22, fig. 52; Naumov, 1969: 245, figs 113, 117A-H; Brinckmann-
Voss, 1970: 76, figs 88-89, pl. 5 figs 1-2; Bouillon, 1971: 333, figs 4.5-7; Millard &
Bouillon, 1973: 12, fig. 1A; Rees, 1979: 300; Calder, 1988: 67, fig. 50; Hirohito, 1988:
41, fig. 12a-b; Schuchert, 1996: 131, fig. 80a-d; Migotto, 1996: 23, fig. 4e-g; Bouillon et
al.,2004: 88, fig. 48B-D.
Coryne stauridia Gosse, 1853d: 257, pl. 16 figs 1-5.
Syncoryne stauridium Krohn, 1853a: 137.
Cladonema Gegenbauri Haeckel, 1879: 109.
Cladonema Krohnii Haeckel, 1879: 109.
Cladonema Dujardinii Haeckel, 1879: 109.
Cladonema Allmani Haeckel, 1879: 109.
Stauridium cladonema Haeckel, 1879: 109.
Cladonema perkinsii Mayer, 1904: 18. pl. 4 fig. 35; Mayer, 1910: 101, pl. 9 fig. 1.
Cladonema mayeri Perkins, 1906: 118; Mayer, 1910: 101, pl. 9 figs 2-3.
Stauridia radiatum –Mayer, 1910: 100.
Eleutheria radiata –Lengerich, 1922: 210, fig. 1; Lengerich, 1923a: 313, figs G-S.
?Cladonema novae-zelandiae Ralph, 1953: 72, fig. 20.
MATERIAL:Aquarium culture of polyp stage originating from the Mediterranean,
18 January 1991, life-cycle observed to mature medusa. – MHNG INVE 29909, Roscoff,
Brittany, polyps on holdfast of laminarian, collected 1 June 2001, cultured at room temperature,
medusae buds developed, very cold-sensitive, died at <14°,grew well at 22-30°C; 16 S sequence
accession number AY512539. – Three medusae, Bay of Portoferraio, Island of Elba, Italy, col-
lected July 2005 by dragging a plankton net over a Posidonia meadow, depth 2-4 m; colour of
whole medusa light brown, 16 S sequence accession numbers of two different individuals
AM088482 and AM088483. – MHNG INVE 37640, 19 February 2004, polyps on "living
stones" from tropical aquarium, origin unknown, medusae cultivated to near maturity, 16 S se-
quence accession number AM088484, appeared identical to other C. radiatum medusae except
that proximal parts of radial canals were white, also on manubrium longitudinal stripes of white
pigment; this material belongs thus perhaps to a separate species of tropical origin, a fact also
suggested by the deviating 16S sequence.
DIAGNOSIS:Hydroid with one oral whorl of capitate tentacles, each with up to
ten gastrodermal cells, with one aboral whorl with usually four filiform tentacles.
Medusa tentacles branched several times, two and more adhesive branches in fully
mature animals, two and more capitate branches; manubrium shorter than bell cavity,
mouth with four to five spherical nematocyst clusters, gonads on manubrial pouches
and on manubrium, radial canals bifurcated or not.
DESCRIPTION:Hydroid colonies stolonal or rarely branched, arising from
creeping, ramified stolons, hydranths on pedicel of variable length, but usually longer
than hydranth. Perisarc smooth, terminating shortly below filiform tentacles.
P.SCHUCHERT
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377
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 18
Cladonema radiatum Dujardin, 1843. A-C, after living material from Brittany; D, after photos
of living Mediterranean medusae. A) Polyp with medusa bud, scale bar 0.2 mm. B) Lateral view
of newly released medusa in optical section, same scale as A. C) Oral view of newly released
medusa. D) Mature male medusa, scale bar ca. 1 mm.

Hydranths with one oral whorl of four to five capitate tentacles, each tentacle with
seven to ten chordoid gastrodermal cells. Below capitate tentacles one whorl of four
(occasionally five) slender, filiform tentacles with a slight terminal swelling, without
nematocysts. Hypostome with an epidermal preoral chamber. Medusae buds naked,
arising above filiform tentacles. Nematocysts: stenoteles and mastigophores.
Newly released medusa with eight to ten bifid tentacles, upper branch with a
terminal nematocyst cluster and a few oral-aboral clusters (Fig. 18).
Adult medusa with bell-shaped umbrella, slightly higher than wide, jelly
moderately thin, sometimes with a slight apical projection, velum rather broad. Medusa
able to swim freely but mostly remains attached, does not move by crawling.
Manubrium spindle-shaped, shorter than or as long as bell cavity, with five (sometimes
four or six) perradial pouch-like protuberances in its middle region, protuberances
rather shallow, size variable. The gonads completely surround the upper two thirds of
manubrium inclusive the pouches. Mouth with four to five bulbous nematocyst
clusters. Radial canals may bifurcate close to the manubrium and eight to ten canals
reach the circular canal, branching pattern variable even in individuals from the same
colony. Number of marginal tentacles corresponds to the number of radial canals. Each
tentacle base with an abaxial ocellus. Marginal tentacles branched, with elongated
thickened base and a long main branch from the underside of which grow one to six
short tentacles acting as adhesive organs, the ends of the adhesive tentacles have a dis-
tinct spherical swelling at their end; distal to the adhesive branches the main branch
gives off up to five side-branches bearing nematocyst clusters alternating in aboral and
oral position and one larger terminal cluster, proximal side-branches originate orally,
more distal ones issuing laterally from the main branch. Colour of stomach and mar-
ginal tentacles red, bright-red or brown; ocelli black or deep crimson. Nematocysts:
stenoteles, desmonemes.
DIMENSIONS:Hydroid colonies up to 25 mm, hydranth about 1 mm; newly
released medusa 0.7-1.0 mm, adult medusa up to 3 mm high. Nematocysts see Weill
(1936), Brinckmann & Petersen (1960), Schuchert (1996).
BIOLOGY:For Mediterranean populations, Brinckmann-Voss (1970) reports that
the polyp colonies remain small in nature (2-3 hydranths), they were found in shaded
placed on algae and other hard substrata. From end of June to the end of July,the
medusae were caught in large numbers in Posidonia beds, later they are rare or absent.
The development of the medusae-buds is quick, at 18°Cit takes only 6-7 days until the
medusa is set free. Also Motz-Kossowska (1905) observed the medusae only from June
to August, rarely also in October.
ADDITIONAL DATA:The polyps of Cladonema radiatum are easy to keep in lab-
oratory. Dujardin (1843) kept them for several years, Lengerich (1923a) reports a
colony that was kept for more than 30 years in an aquarium in Berlin. Also the medusa
is relatively easy to keep and reaches maturity in culture vessels. It also turns up regu-
larly in aquariums. It is thus an ideal experimental organism and therefore there is a
large number of developmental and histological investigations which cannot be re-
viewed here in detail.
P.SCHUCHERT
378

The morphology, histology, and ultrastructure was dealt with in detail by e. g.
Müller (1908); Lengerich (1923a; 1923b), Brien (1942), Bouillon (1968), Bouillon &
Houvenaghel (1970), Tardent & Stössel (1971), Weber & Tardent (1978), Weber (1980,
1981a, 1981b), Bouillon et al. (1988), Falugi et al. (1994).
The nematocysts and their biology were investigated by: Weill (1936), Brien
(1942), Achermann & Tardent (1973), and Bouillon (1971).
The development and medusae budding was investigated by e. g.: Pasteels
(1939, 1941), Brien (1941, 1942), and Bodo (1970).
The behaviour of the medusa is described by: Allman (1872), Browne (1900),
Billard (1905), Lengerich (1923a), and Russell (1953, summary). It is important to
note in this context that the medusa does not crawl like Eleutheria dichotoma, but
changes place by swimming. The adhesive tentacles are thus only used for clinging to
asurface. There is also a differences in the ultrastructure of the adhesive tentacles
(Bouillon, 1968).
The medusae can be hermaphroditic, but usually this is rare (Hartlaub, 1887;
Müller, 1908; Bouillon & Houvenaghel, 1970). Bouillon & Houvenaghel (1970) found
only two hermaphroditic animals among fifty medusae, while others observed none
(Lengerich, 1923a). They can be successive hermaphrodites beginning either as
females or males (Hartlaub, 1887).
DISTRIBUTION:North-Eastern Atlantic: Norway (Christiansen, 1972), Great
Britain and Ireland (Hincks, 1868; Allman, 1872; Russell, 1953), Sweden (Segerstedt,
1889; Aurivillius, 1898; Kramp, 1935); Denmark (Kramp, 1935); Helgoland (Richters,
1908); Holland (Vervoort, 1946), Belgium (Leloup, 1947), Atlantic coast of France
(Dujardin, 1843; Billard, 1905; Teissier, 1965), Atlantic coast of the Iberian Peninsula
(Medel & López-González, 1996). Mediterranean (numerous records, e. g.
Brinckmann-Voss (1970), Boero & Fresi (1986), Daly Yahia et al. (2003, Tunisia),
Bouillon et al. (2004)). Present in the Black Sea (Thiel, 1935). Also known from Brazil
(Migotto, 1996), Bermuda (Calder,1988), Indian Ocean (Millard & Bouillon, 1973), ?
New Zealand (Schuchert, 1996), Japan (Hirohito, 1988; introduced?). Type localities:
Dujardin (1843) described material from the Mediterranean, St. Malo, and Lorient
(France).
REMARKS:The medusa of Cladonema radiatum is quite variable with respect to
the number and branching patterns of the radial canals. Also the number of adhesive
tentacles, manubrial pouches, and oral nematocyst clusters is variable in natural
populations. Even monoclonal animals show some degree of variation.
Weill (1937) examined 106 specimens collected at Bermuda and these encom-
passed the characteristics of C. radiatum, C. perkensii, and C. mayeri.Weill concludes
that the three nominal species were no more than varieties of one rather variable
species, as Mayer (1910) had suggested earlier.This view has been adopted by most
subsequent authors (e. g. Russell, 1953; Kramp, 1959; Kramp, 1961).
There are several nominal Cladonema species known, but sometimes the
differences to C. radiatum are unclear or minimal (Kramp, 1968). Rees (1979) and
Stepanjants et al. (1993) review all the differences between the different nominal
species. Stepanjants et al. (1993) concluded that there were only two valid species,
namely C. radiatum and C. californicum.
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

The medusae of Cladonema californicum Hyman, 1947 was held distinct from
all other described Cladonema in having only one adhesive tentacle branch and one to
two nematocyst bearing branches, and a manubrium that protrudes from the velar
opening (Hyman, 1957; Rees, 1979). According to Hyman (1957), the gonads cover
the manubrium on the pouches and the rest of the manubrium, this in contrast to the di-
agnosis in Kramp (1968). The polyp appears indistinguishable from C. radiatum.
The polyps of the Californian Cladonema myersi Rees, 1949 lack filiform ten-
tacles, the medusa lacks branching radial canals, and the gonad covers the entire
manubrium (Naumov, 1969). Likewise, the polyps of the Japanese Cladonema uchidai
Hirai, 1958 also lack filiform tentacles.
Naumov (1955) described Cladonema pacificum,which he later (1960, 1969)
synonymized with C. myersi. This was contested by Hirohito (1988). Rees (1979) and
Hirohito (1988) think that C. uchidai belongs to Cladonema pacificum.This species is
distinguished from C. radiatum by a gonad that covers almost the whole manubrium,
and not only the upper 2/3 (compare Bouillon et al.,1988: fig. 1).
Cladonema novaezelandiae Ralph, 1953 has been synonymized with C. radia-
tum by Schuchert (1996). However the polyp stage of the New Zealandic Cladonema
remains unknown and it may turn out to be different from C. radiatum. Its synonymy
with C. radiatum is therefore not sufficiently established.
Although it is evident that many nominal Cladonema species are currently not
objectively distinguishable, it is still likely that several distinct biological species have
been included in C. radiatum.The 16S sequences of the Cladonema sample found in
aquarium with tropical material (see above in material examined) differs in more than
25% of its positions from the Atlantic and Mediterranean sequences. Such a difference
represents more likely interspecific variation (comp. Schuchert, 2005). The differences
among the examined European sequences are less than 4%.
The hydroid of Cladonema radiatum is rather difficult to distinguish from
hydroids of some Corynidae (Schuchert, 2001b). Brinckmann & Petersen (1960) found
that the number of gastrodermal cells in the capitate tentacles offers a reliable tool to
discriminate Cladonema radiatum and D. reesi:while C. radiatum has 10 or less cells,
D. reesi has 13-18 (see also Schuchert, 2001b). Additionally, the macrobasic
heteroneme is characteristic for Cladonema radiatum.Also the hydroid of Stauro-
cladia portmanni is very similar.Brinckmann-Voss (1970) found that S. portmanni
polyps have regularly six filiform tentacles, while C. radiatum has usually four,some-
times five.
Genus Eleutheria Quatrefages, 1842
TYPE SPECIES:Eleutheria dichotoma Quatrefages, 1842, by monotypy.
SYNONYMS:Clavatella Hincks, 1861; Herpusa Schmidt, 1869.
REFERENCES:Kramp (1961); Bouillon (1985); Petersen (1990); Bouillon & Boero
(2000).
DIAGNOSIS:Hydroid with an oral whorl of up to ten capitate tentacles, without
aboral filiform tentacles; medusae buds carried in clusters on short blastostyles (gono-
style) or singly at base of hydranth. Medusae adapted for crawling, unable to swim;
umbrella with or without continuous ring of nematocysts along margin; with four or
P.SCHUCHERT
380

more simple and short radial canals; manubrium with broad base, conical, with simple
circular mouth; with or without brood-chamber above base of stomach; gonads either
on manubrium, or in brood-chamber from where they can also extend to the epidermis
of the subumbrella; 6-14 bifurcated marginal tentacles, one upper branch with a single
terminal nematocyst knob, one lower branch with adhesive organ: asexual repro-
duction through medusa budding present.
REMARKS:The problems concerning the distinction of Eleutheria and
Staurocladia have been discussed above under remarks at the family level.
KEY TO THE EUROPEAN ELEUTHERIA MEDUSAE:
1a medusa buds on outside, with brood-chamber . . . . . . . . . . . . . . . Eleutheria dichotoma
1b medusa buds in subumbrella, no brood-chamber . . . . . . . . . . . . . . Eleutheria claparedii
Eleutheria dichotoma Quatrefages, 1842 Figs 19A-C, 20
Eleutheria dichotoma Quatrefages, 1842a: 270, pl. 8;Quatrefages, 1842b: 168; de Filippi, 1866:
375, pl. 1; Hartlaub, 1886: 706, text. fig.; Hartlaub, 1907: 127, figs 119-120; Mayer,
1910: 94, figs 46-48; Müller, 1908: 34, pl. 3 figs 3-7, pl. 4; Lengerich, 1923a: 359, figs
R'-Z', D2; Drzewina & Bohn, 1913: 49, figs 26-37; Weill, 1936: 816; Russell, 1953: 110,
figs 52-53; Kramp, 1961: 59; Naumov, 1969: 249, figs 118-121; Brinckmann-Voss,
1970: 79, figs 90-92; Bouillon, 1994: 146, fig. 55; Bouillon, et al. 2004: 88, fig. 48B-D.
Clavatella prolifera Hincks, 1861: 73, pls 7-8; Hincks, 1868: 73, pl. 12 fig. 2; Allman, 1872: 384,
pl. 18.
Herpusa ulvae O. Schmidt, 1869: 993, fig.
Eleutheria tetranema Haeckel, 1879: 106.
Eleutheria pentanema Haeckel, 1879: 106.
Eleutheria hexanema Haeckel, 1879: 106.
Eleutheria anisonema Haeckel, 1879: 106.
Eleutheria heptanema Haeckel, 1879: 107.
Eleutheria octonema Haeckel, 1879: 107.
Eleutheria dichocnida Haeckel, 1879: 107.
Eleutheria cnidobdella Haeckel, 1879: 107.
Eleutheria dichobdella Haeckel, 1879: 107.
Eleutheria heteroclada Haeckel, 1879: 107.
Cladonema prolifera –Motz-Kossowska, 1905: 47.
Eleutheria krohni Krumbach, 1907: 453.
Eleutheria gemmipara Du Plessis, 1909: 376.
not Eleutheria dichotoma –Claparède, 1863: 4, pl. 1 figs 4-10 [= E. claparedii].
not Eleutheria dichotoma –Spagnolini, 1876: 312 [= E. claparedii].
MATERIAL: MHNG INVE 34228, Mediterranean, Banyuls-sur-Mer, île Grosse, 2 May
2002, 0 m, > 10 medusae on Ulva lactuca,with eggs/planulae in brood-chamber, examined alive,
development to primary polyp followed, DNA sample deposited, 16S sequence accession
number AM088485. – MHNG INVE36841 living polyp colony obtained from B. Schierwater,
collected 1995, Spain, Tossa de Mar, La Fosca, medusae buds developed after a few days of
cultivation.
DIAGNOSIS:Eleutheria medusa with brood-chamber, medusae buds outside on
bell rim or exumbrella, normally six tentacles, tentacles bifurcated once in middle,
trunk and branches of about the same length, often hermaphroditic, nettle ring thick.
DESCRIPTION:Hydroid stolonal, stolons creeping, branched, perisarc smooth;
hydranths with very short pedicels, sometimes almost sessile, pedicel covered by thin
periderm, sometimes widened like a funnel. Hydranth body cylindrical, very extensile,
fully extended with very thin body and swollen terminal region, one oral whorl of four
381
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

to eight capitate tentacles, 16-18 gastrodermal cells per tentacle. Filiform tentacles
absent. Medusae buds in lowest part of hydranth, either singly or in clusters borne on
short gonostyle (tubular outgrowth of body wall, up to four per hydranth), gonostyles
branching or not, carrying up to four medusae buds, buds not protected by periderm
covering. Preoral cavity visible in living animals. Colour: gastrodermis white or pink,
depending on food.
Medusa umbrella somewhat flattened-hemispherical, with its oral surface more
or less six-sided and with well-developed thickened marginal ring packed with nema-
tocysts. Velum broad, usually closing umbrella and opened only when feeding.
Manubrium broadly conical, filling almost the entire subumbrella, extensible beyond
umbrella, mouth simple and without nematocyst knobs. Gonads in specialized cavity
or brood-chamber situated above the manubrium, often male and female gametes
present, female gonads in lower epithelium of brood-chamber, male gonads in upper
epithelium, and also on subumbrella, embryos develop in brood-chamber, up to seven
planulae can be present. Radial canals very short, usually six in number.Ring canal
relatively large, widening at junctions with radial canals. Tentacles hollow proximally,
chordoid distally, mostly six or five present, but rarely also other numbers possible,
bifurcated at about middle, upper branch only with one terminal nematocyst cluster,
lower branch terminating in adhesive organ used to cling to the substratum. One
abaxial ocellus on base of each tentacle. Medusae budding from bell margin and lower
part of exumbrella regularly present, also in reproductive animals. Colours: body olive-
cream, ocelli red to brown. Nematocysts: polyp with stenoteles of two size classes;
medusa with stenoteles and desmonemes.
DIMENSIONS:Polyp 1-6 mm and more, very contractile; tentacular capitula di-
ameter 0.25-0.30 mm. Medusa bell diameter 0.4-0.8 mm, tentacle length 1.8 mm. Egg
size 47-93 µm(Tardent, 1978). Stenoteles of polyp: (30-33.5)x(19-21)µmand (16.5-
18.5)x(9-11)µm. Stenoteles of medusa: (12-24)x(7-16)µm, apparently not falling into
distinct, different size classes. Desmonemes of medusa: (7.5-9.5)x(4-5)µm.
DISTRIBUTION:Present along all coasts of Europe and the Mediterranean, rarer
in the southern North Sea, perhaps absent in the Baltic Sea. Also known from the Black
Sea (Thiel, 1935), Madeira (Friedrich, 1961), and the Caribbean (Spracklin, 1982). The
northernmost occurrence seems to be near Bergen in Norway (Kramp & Damas, 1925).
Records for the Swedish west coast are given by Hartlaub (1886), for the British Isles
by e. g. Hincks (1861, 1868), Allman (1872), for France by e. g. Drzewina & Bohn
(1913) and Teissier (1965), for the Atlantic coast of Spain by Medel & López-González
(1996). The Mediterranean records are summarized in Brinckmann-Voss (1970). Type
locality: Chausey Isles, English Channel.
BIOLOGY:The polyp has only rarely been found in nature. Hincks (1868)
observed that in England medusae budding takes place during summer and autumn.
The medusa lives attached to various seaweeds, preferably on Ulva species, but also on
Cystoseira,Gelidium and other substrata. It lives in shallow depths, also frequently in
tide pools. Brinckmann-Voss (1970) found the medusa also in deeper waters (20 m).
Sexual reproduction in the English Channel was observed in May to June and October
to November (Teissier, 1965).
P.SCHUCHERT
382

ADDITIONAL DATA:Eleutheria dichotoma is easy to keep in small containers and
it has therefore been a favourite subject for a number of studies. Hartlaub (1886) ex-
amined the formation of the brood-chamber in histological sections. The subumbrellar
epidermis forms canal-shaped cavities that penetrate the region above the stomach. The
fusion of these canals in the centre then creates the brood-chamber. The brood-chamber
is connected to the subumbrella by interradial openings (thus usually six). The gastro-
dermis of the manubrium becomes completely separated from the umbrella. The eggs
mature in the lower epithelium of the chamber, while spermatids develop in the upper
epithelium. However, only 12% of Hartlaub’s animals were hermaphroditic, the others
were all female. Müller (1908) supplemented the former observations with more de-
tails. He found that the brood-chamber develops very early in development, even while
the medusa is still attached. The fraction of hermaphroditic animals he found was
higher, namely 35% of the fertile animals. Müller (1908) also reported that the sper-
matogonia can also be produced in small patches of the subumbrellar epidermis.
Krumbach (1907) made many observations on the living animal and he describes its
movements. He found that the velum tightly closes the umbrella. This he considered
might reduce desiccation in case the animal is exposed to the air.Drzewina & Bohn
(1913) studied the variability of the tentacle numbers in animals collected from nature.
They found the following distribution among 39 animals: 1x8 tentacles, 1x7 tentacles,
30x6 tentacles, 7x5 tentacles. They also made regeneration experiments, observed
anomalies, and investigated the influence of cyanide. The budding of medusae from the
medusa bell includes also part of the radial canal, thus the medusa buds are of ento-
and ectodermal origin (Hartlaub, 1886; Lengerich, 1923b). The development of the
medusa bud includes also the formation of an entocodon. The development of the
gametes takes place in the brood-chamber and the planulae are released by a rupture of
the umbrella. The latter heals again after the release (Lengerich, 1923a). The histology
of the medusa has been examined by several authors, e. g. Hartlaub (1886), Lengerich
(1923a), Bouillon (1968), van de Vyver & Bouillon (1969), and Bouillon (1994: fig.
55). Bouillon (1968) also examined the histochemistry and ultrastructure of the
adhesive organs. The haploid chromosome number is 6 (Makino, 1951; cited in
Tardent, 1978). Hauenschild (1956) observed that the ability to produce gametes can
irreversibly be lost in some clones, this either naturally or induced artificially. Hadrys
et al. (1990) examined the feeding behaviour of the medusa. Ender (1997) analyzed the
population structure using mitochondrial DNA sequences. Further experimental,
developmental and structural details are given by Weill (1936), Hauenschild (1957a,
b), Weiler-Stolt (1960), Schierwater (1989), Schierwater & Havenschild (1990),
Schierwater et al. (1991, 1992), Kuhn et al. (1996), Schierwater & Hadrys (1998).
REMARKS:The synonymy is given by Bedot (1912, 1916, 1918), Mayer (1910),
Lengerich (1923a), Kramp (1961), and Russell (1953). In its medusa phase, Eleutheria
dichotoma is very characteristic and among the European medusae it can only be
confounded with E. claparedii.The external medusae buds and the tentacles that are
bifurcating in the middle make E. dichotoma immediately recognizable. In addition, E.
dichotoma has usually five to six tentacles, while most E. claparedii have eight. Their
polyps appear very similar and are perhaps not distinguishable.
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THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

Eleutheria claparedii Hartlaub, 1889 Figs 19D & 21
Eleutheria dichotoma –Claparède, 1863: 4, pl. 1 figs 4-10; Spagnolini, 1876: 312.
[not Eleutheria dichotoma Quatrefages, 1842].
Eleutheria heteronema Haeckel, 1879: 106.
Eleutheria diplonema Haeckel, 1879: 106.
Eleutheria claparedii Hartlaub, 1889: 665; Mayer, 1910: 95, fig. 49; Brinckmann-Voss, 1970:
80, figs 93-95.
Eleutheria claparedei –Hartlaub, 1907: 129, fig. 128; Müller, 1911: 159, pl. 3 fig. 1; Drzewina
& Bohn, 1913: 49, figs 26-37; Lengerich, 1922: 211, fig. 2; Lengerich, 1923a: 336, figs
V-Z, A1-F1; Browne & Kramp, 1939: 274; Kramp, 1961: 59; Bouillon et al., 2004: 88,
fig. 48E-F.
Staurocladia claparedei –Hartlaub, 1917: 401.
MATERIAL: Roscoff, France, September 2004, one medusa in plankton, mature male with
medusae buds; one immature medusa with medusae buds on Cystoseira spec., developed eggs
after 6 weeks of cultivation. 16S sequence of male medusa accession number AM088486.
DIAGNOSIS:Eleutheria medusa without brood-chamber, medusae buds within
subumbrella, usually eight tentacles, tentacles bifurcated once in distal region and
trunk thus clearly longer than branches, gonochoristic, nettle ring not conspicuous.
DESCRIPTION:Sedentary medusa clinging to seaweeds, flat, umbrella slightly
shallower than a hemisphere, without jelly, usually eight to nine tentacles (range 5-10),
not in phase with radial canals, tentacles relatively long when expanded, held hori-
zontal, bifurcated at 1/4 to 1/6 from end, the two branches of equal length, upper
branch ending in a capitulum, capitulum flat-button-shaped to oval, lower tentacle
branch ends in adhesive pad, not much enlarged, used to cling to the substrate. One
abaxial ocellus at base of each tentacle, colour red. Stomach large, filling nearly entire
subumbrella, conical; four to six short radial canals; ring canal thick, underlying nettle
ring inconspicuous but present. Velum conical, broad, usually closed and usually only
opened for feeding, releasing medusae, gametes or excrements. Gonochoristic, gonads
develop in stomach epidermis, without brood-chamber but embryos develop within
subumbrella. Asexual multiplication by medusae budding frequent, buds arise from
epidermis over radial canal in the subumbrellar cavity. Budding usually stops when
gonads develop. Colours: Manubrium and medusae buds orange, rest whitish-cream or
transparent. Nematocysts: stenoteles and desmonemes.
Polyp only known from cultivation experiments, colonies stolonal, swollen
head, one whorl of 4-5 capitate tentacles, no filiform tentacles, further development un-
known.
DIMENSIONS:Medusa bell diameter 0.4-0.5 mm, tentacle length up to 1 mm,
tentacle capitula diameter 90-110 µm. Claparède (1863) reported an egg size of 0.18-
0.3 mm, spawned eggs observed in this study were 0.13 mm in diameter.Nematocysts
of medusa: stenoteles, (11-27)x(8-19)µm, ratio of length to width = 1.5; desmonemes
(9-11.5)x(4.5-6)µm, r=2.0. Polyp 0.7 mm high, tentacles 0.25 mm long (Drzewina &
Bohn, 1913).
DISTRIBUTION:French Channel coast, Mediterranean (Naples). Type locality:
Tahitou near St. Vaast la Hogue (Normandy, France).
BIOLOGY:The medusa was usually found clinging on macroalgae like Ulva
spec. and Fucus spec. in the intertidal zone. In the English Channel, it is most frequent
P.SCHUCHERT
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385
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG. 19
A) Eleutheria dichotoma Quatrefages, 1842, cultivated polyp with medusa bud. B) as in A,
enlarged medusa bud on gonostyle. C) Eleutheria dichotoma, mature medusa, an egg can be faint-
ly seen. D) Eleutheria claparedii Hartlaub, 1889, medusa with two buds in the subumbrella.

in autumn and winter and disappears almost completely in spring (Teissier, 1965).
Asexual production occurs all year round but especially during spring time, animals
with mature gonads were observed from May to June and September to November.
ADDITIONAL DATA:The number of tentacles seems not strictly fixed genetically,
as budded medusae may have other tentacle numbers than the mother medusa
(Drzwina & Bohn, 1913).
Drzewina & Bohn (1913) examined more than 100 medusae and found that
asexual medusae-budding stopped with commencing gonad maturation. One male
animal observed for this study, however, had medusae buds and mature gonads. The
female animal stopped budding before gonad development.
REMARKS:Eleutheria claparedii (original spelling) was named by Hartlaub
(1889) by referring to a description of Claparède (1863) of an animal the latter had
erroneously identified as E. dichotoma.Hartlaub (1889) states that he also found this
species at Naples. He did not designate type material nor a type locality. As Hartlaub
mainly referred to the description of Claparède (1863) based on material from Tahitou
near St. Vaast la Hogue (Normandy, France), and as the major other descriptions of this
species came from this population (Drzwina & Bohn, 1913; Müller, 1911), this loca-
lity is herewith selected as type locality. Hartlaub (1907) introduced the incorrect
spelling E. claparedei,adopted by most subsequent authors. According to the ICZN
[1999, 4th ed.; articles 31.1.1 and 31.1.3], the epithet can be formed in both versions,
but as the spelling in the original publication was Eleutheria claparedii, this spelling
must be used.
Before Hartlaub (1889), Haeckel (1879) had already introduced two new names
for Claparède's animals: Eleutheria heteronema and Eleutheria diplonema. Although
Haeckel's names are senior synonyms, they have never been used as valid names.
Article 23.9.1.1 of the ICZN [1999, 4th ed.] is therefore invoked to declare them as
invalid and Eleutheria claparedii Hartlaub, 1889 the valid name of this species.
Eleutheria claparedii was investigated in detail by Drzewina & Bohn (1913)
and Lengerich (1923a).
The polyp has not yet been identified in the sea and only the young polyp with-
out medusae buds is known from cultivation experiments. Drzewina & Bohn (1913)
found them indistinguishable from young polyps of E. dichotoma.
Genus Staurocladia Hartlaub, 1917
TYPE SPECIES:Eleutheria vallentini Browne, 1902, by designation of Hartlaub (1917).
SYNONYMS:Wandelia Bedot, 1908; Cnidonema Gilchrist, 1919.
REFERENCES:Hartlaub (1917); Gilchrist (1919); Browne & Kramp (1939); Kramp
(1961); Bouillon (1985); Petersen (1990); Bouillon & Boero (2000).
DIAGNOSIS:Hydroid stolonal or sessile, hydranths with an oral whorl of capitate
tentacles, with or without aboral filiform tentacles; medusa buds borne singly on hy-
dranth body immediately above filiform tentacles or in similar position when these are
absent. Medusa adapted to a crawling and walking mode of life, exceptionally still able
to swim; without brood-chamber above manubrium; with or without continuous or
interrupted nematocyst ring along margin; gonads around manubrium or developed on
P.SCHUCHERT
386

387
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE
FIG.20
Eleutheria dichotoma Quatrefages, 1842. A) Medusa with developing embryos in brood-
chamber, after living material, scale bar 0.5 mm. B) Polyp stage obtained from medusa shown
in figure A, scale bar 0.5 mm. C) Polyp with medusae buds, modified after Hauenschild (1956).
D) Schematic organization of the medusa in a vertical section, right half perradial, left half
interradial; modified after Lengerich (1922). Abbreviations: bc brood-chamber with developing
embryos, ct upper branch of tentacle with nematocyst knob (capitulum), e developing eggs, gd
gastrodermis, m mouth, nr nettle-ring, oc ocellus, rc radial canal, s stomach, sf lower branch of
tentacle with adhesive organ, sp male gonad, v velum.

manubrial protrusions; with six to eleven radial canals, some bifurcating shortly distal
to manubrium; mouth circular with or without nematocyst knobs; with up to 60 mar-
ginal tentacles, dichotomous, upper branch with several nematocyst clusters, lower
with adhesive organ; often asexual reproduction by medusa budding or by fission; with
abaxial ocelli at tentacle base.
P.SCHUCHERT
388
FIG. 21
Eleutheria claparedii Hartlaub, 1889. A) after living animal from Roscoff, note the two medusa
buds within the subumbrella (stippled darker), scale bar 0.2 mm. B) Young hydranth, after
Drzewina & Bohn (1913).

REMARKS:The problems concerning the distinction of Eleutheria and
Staurocladia have been discussed above under "Remarks" at the family level. There is
only one species in the European fauna.
Staurocladia portmanni Brinckmann, 1964 Fig. 22
Staurocladia portmanni Brinckmann, 1964: 693, figs 1-10; Brinckmann-Voss, 1970: 82, figs 96-
98, pl. 6 figs 1-3; Bouillon et al., 2004: 90, fig. 48I-J.
MATERIAL EXAMINED:Staurocladia portmanni,syntypes BMNH 1963.12.10.2, Ischia,
Naples, 2 mature medusae. – Staurocladia portmanni syntype BMNH 1963.12.10.1, Italy, Gulf
of Sorento, Vico Equense, polyp colony.
DIAGNOSIS:Hydroid with one oral whorl of capitate tentacles and an aboral
whorl of six filiform tentacles, short perisarc covered pedicel, medusae budded directly
from hydranth body above filiform tentacles. Medusa clinging and creeping on sub-
stratum, but also able to swim freely, five to ten branched radial canals, each sending
aprotuberance into mesogloea, 18-24 tentacles, bifid, nematocyst clusters terminal and
on oral and aboral sides of upper branch, plus an additional lateral pair near branching
point; five interradial manubrial pouches; gonad surrounds entire manubrium; mouth
with five nematocyst clusters.
DESCRIPTION (after Brinckmann, 1964; Brinckmann-Voss, 1970; Bouillon,
1966; and own observations): Hydroid forming small, stolonal colonies. Stolons
ensheathed by perisarc which extends up to the short pedicel; hydranth with three to
five capitate tentacles in an oral whorl and six filiform tentacles at base of hydranth
body, number of filiform tentacles constant; usually one, rarely two medusae buds
above filiform tentacles. Preoral cavity present. Nematocysts: stenoteles. Colour: pink-
orange. Medusa-bud development very slow, taking up to 50 days.
Newly liberated medusa 0.6-0.7 mm in diameter; seven to nine tentacles, bifid,
oral branch with terminal adhesive end, upper branch short and with one terminal
nematocyst cluster, sometimes also an additional aboral one, two lateral nematocyst
clusters on common trunk near bifurcation always present; five to ten radial canals,
number not increasing with further development, protuberances small.
Adult medusa with bell-shaped umbrella, wider than high. Manubrium not
extending beyond velum, with five protruding stomach-pouches in middle, mouth with
five spherical nematocyst clusters. Gonads surround manubrium and stomach pouches
without perradial interruptions, gonads get separated into five sections only where
radial canals are adnate to top of the manubrium; gonochoristic, no medusa budding.
Five radial canals originating near centre of top of manubrium, then sandwiched
between subumbrella and broad base of manubrium for a third of their length, some
branching dichotomously so that up to ten radial canals reach the circular canal, at
upper third of each radial canal an upright, finger-like protuberance that penetrates into
mesogloea; radial canals widen bulb-like before joining circular canal. Tentacles 16-25
in number, hollow, lumen communicates with circular canal; each tentacle bifurcated
at about the middle; lower branch with terminal adhesive pad; upper branch with
terminal nematocyst cluster (capitulum), plus two to five aboral, and two to four aboral
nematocyst clusters; common trunk bears additionally two lateral nematocyst clusters
near branching point. Each tentacle contains one basal, abaxial ocellus. Border
389
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

between exumbrella and velum is thickened with nematocysts. Colours: gastrodermis
of stomach, circular canal, and tentacles red-orange; upper part of radial canals and
protuberances contain a white pigment, same pigment is also found in the distal part of
radial canals where they widen and join circular canal. Nematocysts: stenoteles,
desmonemes, and a large, unidentified capsule.
DIMENSIONS:Hydranth body 1.5-2 mm in height, Adult medusa 4-6 mm in
diameter,bell-height 2.5-5 mm.
P.SCHUCHERT
390
FIG. 22
Staurocladia portmanni Brinckmann, 1964, modified after Brinckmann-Voss (1964), above: ma-
ture medusa, below: polyp with medusa bud. For size see text.

DISTRIBUTION:Only known from the region of Naples (Tyrrhenian Sea,
Mediterranean). The material used for the original description came from the Gulf of
Sorrento (polyp stage) and the island of Ischia (medusa). Under type locality,
Brinckmann (1964) gives only the registration number BMNH 1963.12.10.1. Accor-
ding to the label of this specimen in the BMNH, it came from Vico Equense in the Gulf
of Sorrento and this locality must therefore be assumed to be the type locality.
BIOLOGY:The medusae of S. portmanni are found in Posidonia oceanica beds
in depths of 15-35 m from end of May to begin of July. The hydroid was found on algae
like Udothea sp. and Halimeda tuna in a depth of 30 m. The medusa development is
extraordinarily slow, it takes up to 50 days from the first bud to the liberation and
another 40-60 to sexual maturity.
The medusa of S. portmanni is able to creep as well as to swim freely. More
details on its behaviour are given in Brinckmann-Voss (1970).
Genus Dendronema Haeckel, 1879
TYPE SPECIES:Dendronema stylodendron Haeckel, 1879 by monotypy.
REFERENCES:Haeckel (1879); Kramp (1961); Bouillon & Boero (2000).
DIAGNOSIS:Cladonematidae with branched oral tentacles; umbrella bell-shaped,
with an apical cavity above manubrium.
REMARKS:A problematic genus containing a single, doubtful species, see dis-
cussion below.
Dendronema stylodendron Haeckel, 1879 Fig. 23
Dendronema stylodendron Haeckel, 1879: 110, pl. 7 fig. 8; Lengerich, 1922: 210; Kramp, 1955:
307; Kramp, 1959: 96; Kramp, 1961: 58.
MATERIAL:None examined, likely no type material exists.
DIAGNOSIS:As for genus.
DESCRIPTION (after Haeckel, 1879): Umbrella bell shaped, height 9 mm,
diameter 6 mm; with pointed, conical apical process, nearly twice as high as broad.
Manubrium spindle-shaped, continued into mesogloea as apical cavity,in proximal
half with four egg-shaped gonads, mouth with four dichotomously branched oral
tentacles (50-60 ends) reaching down to velum level. Four radial canals that divide
close to manubrium into two branches. Eight tentacles, each with an ocellus that has a
lens, each tentacle divided into two principal branches, of which the adaxial one
branches two times and bears four adhesive ends, the abaxial branch divides dichoto-
mously several times and bears many nematocyst knobs. Colours: manubrium and
apical cavity reddish-yellow; tentacles, radial- and circular canals red; ocelli black.
DISTRIBUTION:Known from original description only, type locality: Lanzarote,
Canary Islands.
REMARKS:Besides its first description, Dendronema stylodendron has never
been reported again and some authors doubted its existence, e. g. Lengerich (1923a)
lists it as a synonym of Cladonema radiatum. Kramp (1955, 1961) thought that this is
391
THE EUROPEAN ATHECATE HYDROIDS AND THEIR MEDUSAE

unlikely,but nevertheless classified it as doubtful (Kramp, 1959). Haeckel based his
description of on a living specimen he collected at Lanzarote. The animal is remark-
ably large for this family and his drawings are quite detailed. So, it seems quite
unlikely that Haeckel confounded it with the much smaller Cladonema radiatum.
However, the species remains somewhat doubtful until it can be found again.
ACKNOWLEDGEMENTS
This study was made possible through a SYNTHESIS grant of the European
Union that enabled me to examine hydrozoans of the Natural History Museum in
London. I also wish to express my sincere thanks to the museums of Copenhagen,
Bergen, Bruxelles, and Hamburg which provided valuable loans of material. Many
thanks are also due to Dr B. Schierwater who provided a culture of E. dichotoma, Dr
M. Stierwald who provided photos of Cladonema radiatum,and Dr W. Vervoort who
gave me valuable taxonomic advice on the validity of C. cocksii.Mrs J. Pralong kind-
ly made the serial histological sections. I would also like to thank Dr F. Boero, Dr D.
Calder, and Dr A. Marques who commented on initial versions of the manuscript.
However,this is not meant to delegate my responsability for the content and all short-
comings and errors are mine alone.
P.SCHUCHERT
392
FIG.23
Dendronema stylodendron, after Haeckel 1879.

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