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Aquatic Invasions (2019) Volume 14, Issue 1: 21–58
Special Issue: Marine Bioinvasions of the Galapagos Islands
Guest editors: Amy E. Fowler and James T. Carlton
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 21
CORRECTED PROOF
Research Article
Hydroids (Cnidaria, Hydrozoa) from marine fouling assemblages
in the Galápagos Islands, Ecuador
Dale R. Calder1,2,*, James T. Carlton3, Kristen Larson4, Jenny J. Mallinson5, Henry H.C. Choong6, Inti Keith7
and Gregory M. Ruiz4
1Department of Natural History, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario M5S 2C6, Canada
2Research Associate, Royal British Columbia Museum, 675 Belleville Street, Victoria, British Columbia V8W 9W2, Canada
3Williams College-Mystic Seaport Maritime Studies Program, Mystic, Connecticut 06355, USA
4Smithsonian Environmental Research Station, 647 Contees Wharf Road, Edgewater, Maryland 21037, USA
5School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton SO14 3ZH, UK
6Royal British Columbia Museum, 675 Belleville Street, Victoria, British Columbia V8W 9W2, Canada
7Charles Darwin Foundation, Marine Science Department, Santa Cruz Island, Galápagos, Ecuador
Author e-mails: dalec@rom.on.ca (DRC), james.t.carlton@williams.edu (JTC), larsonk@si.edu (KL), jxm@noc.soton.ac.uk (JJM),
hchoong@royalbcmuseum.bc.ca (HHCC), inti.keith@fcdarwin.org.ec (IK), ruizg@si.edu (GMR)
*Corresponding author
Abstract
An account is given of hydroids collected in 2015 and 2016 from port and harbor
fouling communities in the Galápagos Islands. Also included is the hydroid of
Ectopleura media, discovered on the wreck of the tanker Jessica near Isla San
Cristóbal in 2001. Among 20 species reported herein were six anthoathecates and
14 leptothecates. Most common in the samples were the kirchenpaueriid Ventromma
halecioides and the halopteridid Halopteris alternata. Eight species (Bougainvillia
muscus, Bimeria vestita, Clytia elongata, C. obliqua, C. thornelyi, Obelia oxydentata,
Eucheilota sp., and Halecium labiatum) are reported for the first time from the
Galápagos archipelago. Three of them (Clytia elongata, C. thornelyi, and Halecium
labiatum) are also new to the eastern Pacific. Seven species treated here are
considered introduced by shipping to the islands, bringing to eight the number of
introduced hydroids. In addition, we treat four species as cryptogenic, bringing to
five the total number of the latter in the Galápagos. The binomena Obelia thornelyi
Nutting, 1927, Clytia stolonifera Blackburn, 1938, and C. latitheca Millard and
Bouillon, 1973 are regarded as synonyms, with the first of these having
nomenclatural priority. Meanwhile, the senior synonym O. thornelyi is reassigned
to the genus Clytia Lamouroux, 1812 as C. thornelyi. Another species in the samples,
Dynamena distans Lamouroux, 1816 (also widely known as Sertularia distans and
Tridentata distans), is combined for the first time with the genus Amphisbetia
L. Agassiz, 1862, as A. distans.
Key words: Hydroidolina, marine invertebrates, Medusozoa, species introductions,
cryptogenic, invasion, taxonomy, Tropical Eastern Pacific Realm
Introduction
Hydroids of the Galápagos Islands have received only modest attention.
The most comprehensive contributions to knowledge of the group in the
region are by Fraser (1938a, b, 1948) on collections acquired in the archipelago
Co-Editors’ Note: This is one of the
papers from the special issue of Aquatic
Invasions on marine bioinvasions of the
Galápagos Islands, a research program
launched in 2015 and led by scientists
from the Smithsonian Environmental
Research Center, Williams College, and
the Charles Darwin Research Station of
the Charles Darwin Foundation. This
Special Issue was supported by generous
funding from the Galápagos Conservancy.
Citation: Calder DR, Carlton JT, Larson
K, Mallinson JJ, Choong HHC, Keith I,
Ruiz GM (2019) Hydroids (Cnidaria,
Hydrozoa) from marine fouling
assemblages in the Galápagos Islands,
Ecuador. Aquatic Invasions 14(1): 21–58,
https://doi.org/10.3391/ai.2019.14.1.02
Received: 17 August 2018
Accepted: 10 January 2019
Published: 28 March 2019
Handling editor: Amy Fowler
Copyright: © Calder et al.
This an open access article published under terms
of the Creative Commons Attribution License
(Attribution 4.0 International - CC BY 4.0).
OPEN ACCESS.
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 22
during the Allan Hancock Pacific Expeditions of 1931–1932, 1933, 1934,
and 1938. Earlier, Clarke (1907) reported three species collected during the
1904–1905 cruise of the United States Fish Commission Steamer Albatross.
Hastings (1930) added a new species of zancleid (Zanclea protecta) from
James Island (Isla Santiago) and from Pánama (type locality: Isla Taboga).
Houvenaghel and Houvenaghel (1974) identified one hydroid (Dynamena
crisioides Lamouroux, 1824) to species, and mentioned several others that
were identified to genus only, in an investigation on vertical zonation of rocky
intertidal biota at Isla Santa Cruz. Best known of all hydrozoans in the
Galápagos is the family Stylasteridae Gray, 1847. Cairns (1986) reviewed
earlier studies on stylasterids from the islands and provided accounts of 14
species, nine of them as new. Cairns (1991) added another new species, but
the total number remained at 14, with one earlier species being placed in
synonymy. Additions to the general hydroid fauna, and a checklist of
species, were provided by Calder et al. (2003). Marshall et al. (2002) and
Marshall and Edgar (2003) called attention to hydroids discovered on and
adjacent to the wreck of the oil tanker Jessica off Isla San Cristóbal in 2001.
A Galápagos field guide by Hickman (2008) included accounts of 12 of the
more prominent hydroid species. In an overview of the local marine
invertebrate fauna (Hickman 2009), bryozoans and hydroids were reported
to be two of the more diverse groups. Including 14 stylasterids (Cairns
1991) and 96 others (Calder et al. 2003), 110 species have been recorded
from the islands.
Most previous investigations of hydroids in the Galápagos have focused
on species from natural habitats. The present study is based primarily on
hydroids found as part of fouling communities, particularly those in ports
and harbours.
Materials and methods
Hydroids from the Galápagos Islands examined here were obtained during
surveys for invasive species in February 2015 and April 2016. Manual
collecting from docks and pilings was undertaken in the vicinity of Puerto
Ayora (Isla Santa Cruz) and at Isla Baltra (Figure 1). A single sample came
from Isla Bartolomé. In addition, in April 2016, fouling panels [14 × 14 cm,
0.5 cm thick, grey polyvinyl chloride (PVC) plates, lightly sanded on the
underside to optimize attachment conditions, and suspended horizontally
at a depth of 1 m] that had been deployed 14 months or 3 months earlier in
February 2015 and January 2016 respectively at (1) the Puerto Ayora main
passenger docks, (2) a private dock in Franklin’s Bay, Puerto Ayora, both
on Santa Cruz Island, and (3) on a Navy floating dock on Baltra Island,
were retrieved. Voucher samples of hydroids (and other taxa) were removed
and preserved in 95% ethanol. An additional sample of hydroids was
collected from the wreck of the oil tanker Jessica at Isla San Cristóbal in
2001 by G. Edgar and P. Marshall.
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 23
Figure 1. Sampling locations in the Galapágos Islands, Ecuador. Inset shows location of the
archipelago, west of continental South America. Station 1, Isla Baltra, navy dock, −0.436364;
−91.297469; Station 2, Isla Santa Cruz, Puerto Ayora main passenger dock, −0.747828;
−90.312564; Station 3, Isla Santa Cruz, Franklin’s Bay, −0.755194; −90.312653; Station 4, Isla
San Cristóbal, wreck of tanker Jessica, −0.894728; −89.619889. Station 5, Isla Bartolomé,
−0.279608; −90.556714; Station 6, Isla Santa Cruz, Tortuga Bay, −0.763792; −90.340253. Map
courtesy of Linda McCann.
Collections are deposited at the Smithsonian Environmental Research
Station (SERC), Edgewater, Maryland, USA, and at the Charles Darwin
Research Station, Puerto Ayora, Santa Cruz Island, Galápagos, Ecuador.
Specimens of one species (Ectopleura media) are in collections of the
Invertebrate Zoology Section at the Royal Ontario Museum.
The classification system adopted here generally follows Schuchert
(2012) for anthoathecates and Maronna et al. (2016) for leptothecates. A
synonymy list accompanying each species includes the original binominal
name together with its author and date, along with citations of any
publications providing primary records of hydroids from the Galápagos
Islands. All cited references have been examined as part of the study.
Illustrations are based entirely on hydroids included herein.
Abbreviations are as follows:
JJM Hyd. Jenny Mallinson Galápagos hydroid collection, University of
Southampton, Southampton, UK
NMNH National Museum of Natural History, Smithsonian Institution,
Washington, DC, USA
ROMIZ Invertebrate Zoology collections, Royal Ontario Museum,
Toronto, Ontario, Canada
SERC Galápagos collections, Smithsonian Environmental Research
Center, Edgewater, Maryland, USA
WoRMS World Register of Marine Species
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 24
Results
Twenty species (six anthoathecates and 14 leptothecates) are reported here,
eight of which are new to the islands (Table 1, Supplementary material
Table S1). We note whether species may be cryptogenic or introduced, but
otherwise we consider the species treated here as native (although whether
they should bear the names of “cosmopolitan” species with type localities
in other oceans often remains to be determined).
Unless otherwise stated, all vials referred to are SERC numbers.
Systematic Account
Phylum Cnidaria Verrill, 1865
Class Hydrozoa Owen, 1843
Superorder Anthoathecata Cornelius, 1992a
Order Aplanulata Collins, Winkelman, Hadrys and Schierwater, 2005
Family Tubulariidae Fleming, 1828
Ectopleura media Fraser, 1948
Figure 2a, b
Ectopleura media Fraser 1948: 201, pl. 22, figs. 2a–d.–Marshall et al. 2002: 92, photos 14, 15.–
Calder et al. 2003: 1198.–Marshall and Edgar 2003: 294.–Hickman 2008: 124, three unnumbered
figs.–Calder et al. 2009: 940.
Material.—Isla San Cristóbal, on wreck of the tanker Jessica, 10 May 2001,
1 colony, 2.5 cm high, some hydranths with developing gonophores, coll.
G. Edgar and P. Marshall, ROMIZ B3479.
Remarks.—The type locality of Ectopleura media Fraser, 1948, presently
known only from the Galápagos, is Bindloe Island (Isla Marchena). It has
also been reported from Punta Vicente Roca, Isla Isabela (Calder et al.
2003) and Isla San Cristóbal (Marshall et al. 2002; Marshall and Edgar 2003).
At the latter location, specimens were found on and adjacent to the wreck
of the oil tanker Jessica, which grounded off Puerto Baquerizo Moreno on
16 January 2001. By May 2001, when assessments were undertaken by
Marshall and colleagues, colonies of the hydroid were a conspicuous
component of the fouling assemblage on and adjacent to the wreckage.
Fraser (1948) believed that gonophores of Ectopleura media were
medusa buds. However, from specimens observed previously in the
Galápagos by us, they are medusoids that do not become released as free
medusae. In that, they differ from those of the sympatric E. integra (Fraser,
1938a), whose type locality is Isla Baltra, Galápagos (Calder et al. 2009).
Gonophores of E. crocea (L. Agassiz, 1862), reported from Isla Isabela by
Fraser (1938a), are sporosacs, with those of the female having 6–8 crest-like
processes distally (Schuchert 2010). Fraser’s record of E. crocea from the
archipelago has been considered doubtful (Calder et al. 2003: 1205), as it is
a species more characteristic of cool temperate than tropical waters.
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 25
Table 1. Introduced and cryptogenic Hydrozoa of the Galápagos Islands (* treated herein).
Species
Status
I, Introduced
C, Cryptogenic
Galápagos collection
records
Possible
Origin Remarks
Bougainvilliidae
*Bougainvillia
muscus
I 2016 (Baltra) North Atlantic? Mills et al. (2007) and Carlton and Eldredge
(2009, 2015) regard it as an introduction to the
northeast Pacific Ocean and to the Hawaiian
Islands, respectively, as well
*Bimeria
vestita
C 2016
(Santa Cruz)
unknown Considered cryptogenic because of a possible
global species complex; reported from 1930s
collections from Ecuador, Pánama, and Mexico
(see text); introduced to the Hawaiian Islands
(Carlton and Eldredge 2015; see also Calder 2010)
Cirrholoveniidae
*Cirrholovenia
tetranema
C 1992 (Daphne Chica,
Española); 1994 and
2015 (Santa Cruz);
2000 (Isabela)
Indo-west Pacific? Considered cryptogenic because of a possible
global species complex
Clytiidae
*Clytia
elongata
I 2016
(Santa Cruz)
Australia-New
Zealand
First report from the eastern Pacific Ocean;
reported as Clytia ? elongata (identified by P.M.
Ralph) on New Zealand ship hulls (Skerman 1960)
*Clytia
thornelyi
I 2016
(Baltra, Santa Cruz)
western Pacific or
western Atlantic
First report from the eastern Pacific Ocean
Clytia
hummelincki
I 1992 (San Cristobal),
2000 (Wolf)
Caribbean (via the
Panama Canal) or
the Indo-west
Pacific
Reported earlier from the Galápagos Islands
(Calder et al. 2003). A species demonstrating an
invasion propensity (Gonzalez-Duarte et al. 2016),
having arrived in the Mediterranean in the 1990s;
records since the 1980s from the Indo-west
Pacific (summarized in Gonzalez-Duarte et al.
2016) may represent recent introductions as well
Obeliidae
*Obelia
dichotoma
C 1930s (Floreana,
Baltra, Isabela); later
collections from
Fernandina,
Espanola, Santa Cruz
unknown Considered cryptogenic because of a possible
global species complex
*Obelia
oxydentata
I 2016
(Santa Cruz)
western Atlantic or
western Pacific
Previously known from the eastern Pacific based
on a Pánama record from 1904–1905
Haleciidae
*Halecium
labiatum
I 2016 (Baltra) western Indian
Ocean
*Nemalecium
lighti
I 2005–2007 (Wolf,
Darwin, Marchena);
2016 (Santa Cruz)
Indo-west Pacific
or western Atlantic
Pennariidae
Pennaria
disticha
C 1930s (Wolf,
Floreana); 1992
(San Cristobal), 1994
(Tortuga), 1998–99
(Marchena, Espanola);
2005–2007 (Darwin,
Marchena)
unknown 1930s–1990s records: Calder et al. 2003; 2005–07
record: Banks et al. 2009. Considered cryptogenic
because of a possible global species complex;
Carlton and Eldredge (2009), review its previous
designations as cryptogenic or introduced in the
Pacific theater
Kirchenpaueriidae
*Ventromma
halecioides
C 1999 (Fernandina);
2016 (Santa Cruz)
unknown Considered cryptogenic because of a possible
global species complex; Carlton and Eldredge
(2009) also considered it cryptogenic in the
Hawaiian biofouling fauna
Halopterididae
*Halopteris
alternata
I 2016
(Santa Cruz)
Atlantic Ocean
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 26
Figure 2. Anthoathecata: families Tubulariidae, Oceaniidae, Bougainvilliidae, and Eudendriidae.
a, Ectopleura media, hydranth and distal end of hydrocaulus, Isla San Cristóbal, ROMIZ
B3479, scale equals 0.5 mm. b, Ectopleura media, proximal end of hydrocaulus, showing
annulated base, ROMIZ B3479, scale equals 0.5 mm. c, ?Turritopsis sp., hydranth, Isla Santa
Cruz, Puerto Ayora, main passenger dock, SERC #234288, scale equals 0.2 mm. d, Bougainvillia
muscus, part of colony, with two hydranths and two stolons, Isla Baltra, navy dock, SERC #232848,
scale equals 0.25 mm. e, ?Bougainvillia sp., hydranth and distal end of pedicel, Isla Santa Cruz,
Puerto Ayora, main passenger dock, JJM Hyd. 4, scale equals 0.1 mm. f, Bimeria vestita, colony
with three hydranths, Isla Santa Cruz, SERC #02611, scale equals 0.2 mm. g, Eudendrium (?)
breve, hydranth and pedicel, Isla Santa Cruz, Tortuga Bay, scale equals 0.2 mm.
Order Filifera Kühn, 1913
Family Oceaniidae Eschscholtz, 1829
?Turritopsis sp.
Figure 2c
Material.—Isla Santa Cruz, Puerto Ayora, main passenger dock, on fouling
plate deployed 27 February 2016, retrieved April 2016, 2 colonies, up to 3 mm
high, without gonophores, coll. K Larson, vial 234288.
Remarks.—Although these specimens lacked gonophores and appear to
have been quite young, they are unmistakably oceaniids. The colonies are
similar to stolonal hydroids from Fiji that Gibbons and Ryland (1989)
identified as Tubiclava sp. They also resemble Tubiclava triserialis Fraser,
1938a, a species inquirenda originally described from the Islas Revillagigedo
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 27
of Mexico in the warm eastern Pacific. As for Tubiclava Allman, 1863,
Schuchert (2004) justifiably regarded it as a genus of doubtful identity that
should no longer be recognized as valid. Another hydroid of somewhat
similar morphology is that of Oceania armata Kölliker, in Gegenbaur et al.,
1853. While the medusa stage of that species is widely distributed and well-
known, its hydroid had until recently been known only as juveniles from
laboratory cultures of Mediterranean material (Metschnikoff 1886; Schuchert
2004). However, the medusa of O. armata has now been linked by Schuchert
(2016) to the hydroids of Turritopsis chevalense (Thornely, 1904) and
T. fascicularis Fraser, 1943 via DNA barcoding. Hydroids of both nominal
species are relatively large and polysiphonic, and distinct from the miniscule
ones observed here. There is no record of this hydromedusa, or of the
hydroids above, in the tropical eastern Pacific.
In having clavate hydranths with scattered filiform tentacles, a
prominent hypostome, and an exoskeleton comprising non-nested tubes of
perisarc, we have assigned our specimens with question to the oceaniid
genus Turritopsis McCrady, 1857. Further identification to species level on
the basis of morphology is inadvisable based on the available material. The
oceaniid T. nutricula McCrady, 1857 has been recorded earlier in the
Galápagos from Isla Isabela (Fraser 1938a) and Isla Wolf (Calder et al. 2003).
If our hydroid is indeed T. nutricula, a species originally described from
Charleston, South Carolina, USA, and reported worldwide in temperate
and tropical waters, shipping would be a likely means of introduction.
As for Turritopsis nutricula, molecular studies now indicate the probable
existence of a species complex hidden under that name. According to
Miglietta et al. (2007) and Miglietta and Lessios (2009), the hydrozoan
originally assigned that binomen may be restricted in distribution to the
western Atlantic Ocean. Related species originally described from the
Indo-Pacific region, and their type localities, include T. rubra (Farquhar,
1895) from Wellington Harbour, New Zealand, T. lata von Lendenfeld,
1885 from Port Jackson, Australia, T. pacifica Maas, 1909 from Sagami
Bay, Japan, T. chevalense from Sri Lanka (Gulf of Manaar), and T. minor
Nutting, 1905 from Maui, Hawaii. Of these, molecular sequencing has been
undertaken to date on T. rubra, T. lata, and T. chevalense (=Oceania armata).
Species limits and distributions within the genus remain obscure, and our
sterile material is identified here simply as ?Turritopsis sp.
Family Bougainvilliidae Lütken, 1850
Bougainvillia muscus (Allman, 1863)
Figure 2d
Perigonymus muscus Allman 1863: 12.
Material.—Specimens collected in April 2016 from fouling plates deployed
at the Isla Baltra navy dock, 15 January 2016, coll. K. Larson: 1 colony
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 28
fragment, 3 mm high, without gonophores, vial 234218; 3 colony
fragments, up to 5.5 mm high, without gonophores, vial 232875; 3 colony
fragments, up to 5 mm high, without gonophores, vial 232858; 10 colony
fragments, up to 10 mm high, without gonophores, vial 232848; 2 colony
fragments, up to 7 mm high, without gonophores, vial 234192; 1 colony
fragment, 4 mm high, without gonophores, vial 232869.
Remarks.—These hydroids, although sterile, were assigned to Bougainvillia
muscus (Allman, 1863) based on their similarity to colonies studied earlier
in Hawaii (Calder 2010). The latter specimens had been identified after
examination of both hydroid and medusa stages. As noted earlier, B. muscus
is presumably a eurytopic Atlantic species (type locality: Devon, England)
that has also been reported in temperate and tropical waters of the Pacific
and Indian oceans. Molecular data revealing low divergence values
between populations from Europe and New Zealand (Schuchert 2007)
support the conclusion that the species is widely distributed. Its hydroid is
sometimes part of the fouling community in ports and canals (Billard 1926,
as B. ramosa muscus; Millard 1959, as B. ramosa; Schuchert 1996; Calder
2010), as in this study, suggesting that long-range transport has been effected
by shipping. Reports of the species from several other remote oceanic
islands, including Bermuda (Calder 1988), New Zealand (Schuchert 1996),
and Hawaii (Calder 2010), also provide evidence of its capacity for human-
mediated dispersal. The medusa stage of B. muscus is also known to have a
wide geographic range. While most accounts of it are from the eastern
North Atlantic and Mediterranean Sea (Kramp 1961, as B. ramosa),
records also exist from the Pacific and Indian oceans (Bouillon 1980, as B.
ramosa; Navas-Pereira and Vannucci 1991, as B. ramosa; Schuchert 1996;
Santhakumari and Nair 1999, as B. rumosa; Xu et al. 2014a).
Information on the biology of Bougainvillia muscus has been
summarized by Schuchert (2007). This constitutes the first record of the
species, a likely introduction, from the Galápagos Islands.
?Bougainvillia sp.
Figures 2e; 5a
Material.—All but the last are specimens from fouling plates retrieved in
April 2016 at the main passenger dock, Puerto Ayora, Isla Santa Cruz, coll.
K. Larson: plate deployed 27 February 2015, 1 colony fragment, 3 mm high,
without gonophores, vial 234289; plate deployed 15 January 2016, 1 colony,
2 mm high, without gonophores, vial 234057; plate deployed 15 January
2016, 1 colony fragment, 2 mm high, without gonophores, vial 234064.–
Isla Santa Cruz, Puerto Ayora, port, 26 April 2016, 1 colony, 2 mm high,
without gonophores, coll. J. J. Mallinson, JJM Hyd. 4.
Remarks.—This miniscule hydroid appears to be a species of Bougainvillia
Lesson, 1830, or at least a bougainvilliid. A note by one of us (JJM) indicates
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 29
that in life it had a “tall hypostome”. In preserved material, the hypostome
was dome-shaped. The colony was stolonal, and hydranth pedicels tapered
very gradually from distal to proximal end. In lacking gonophores,
identification to species is impossible based on morphology.
Bimeria vestita Wright, 1859
Figure 2f
Bimeria vestita Wright 1859: 109, pl. 8, fig. 4.
Material.—Isla Santa Cruz, Puerto Ayora, Puerto Ayora dock, fouling
community on floats, 22 February 2015, 8 colony fragments, up to 6 mm
high, with gonophores, coll. G. Ruiz and M. Torchin. –Isla Santa Cruz,
Tortuga Bay, from rotten wood on beach, February 2015, 4 colony
fragments, up to 8 mm high, without gonothecae, coll. L. McCann and J.T.
Carlton, SERC field catalog #02611. –Isla Santa Cruz, Puerto Ayora,
fouling on docks, February 2015, 9 colony fragments, up to 4 mm high,
without gonophores, coll. J.T. Carlton, G. Ruiz and L. McCann, SERC field
catalog #02013. –Isla Santa Cruz, Puerto Ayora, main passenger dock,
collected April 2016 from fouling plate deployed 27 February 2015, 2 colonies,
up to 7 mm high, one with gonophores, coll. K. Larson, vial 233131.
Remarks.—These hydroids are referable to the genus Bimeria Wright,
1859, and they correspond morphologically with B. vestita Wright, 1859.
Earlier, Fraser (1938a, b) reported the species from the coast of Ecuador, as
well as from the Pacific coasts of Mexico and Pánama. This is the first
record of the species, or one like it, from the Galápagos. A distinct variety
of the species (B. vestita forma nana) was described from Sri Lanka by
Leloup (1932), and he identified it again from Vietnam (Leloup 1937).
Confirmation is needed whether populations identified as B. vestita from
warm waters of the Pacific are the same as Wright’s (1859) species from the
Firth of Forth, Scotland. Worldwide distribution records are summarized
by Schuchert (2007), with reports of the species from temperate and
tropical waters of the Atlantic, Pacific, and Indian oceans. We consider
B. vestita to be cryptogenic in the Galápagos.
Fraser (1938a) reported three species of Bimeria from the Galápagos
(B. gracilis Clark, 1876; B. tenella Fraser, 1925; B. laxa Fraser, 1938a), but all
have been reassigned to the genus Garveia Wright, 1859 (Calder et al. 2003).
Family Eudendriidae L. Agassiz, 1862
Eudendrium (?) breve Fraser, 1938a
Figure 2g
Eudendrium breve Fraser 1938a: 18, pl. 3, fig. 13. –Calder et al. 2003: 1194. –Calder et al. 2009: 933.
Material.—Isla Santa Cruz, Tortuga Bay, fouling community on dead
intertidal mangrove roots, 23 February 2015, 2 colony fragments, up to 5 mm
high, without gonophores, coll. J.T. Carlton. –The following specimens
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 30
collected April 2016 from fouling plates deployed at Puerto Ayora main
passenger dock, Isla Santa Cruz, 27 February 2015, coll. K. Larson: 1 colony
fragment, 5 mm high, without gonophores, vial 233131; 3 colony fragments,
12 mm high, without gonophores, vial 234122; 1 colony, 2 mm high, without
gonophores, vial 233133; the same, but plates deployed 15 January 2016:
1 colony fragment, 6 mm high, without gonophores, vial 234098; 1 colony,
1 mm high, without gonophores, vial 233016; 1 colony, 3 mm high, without
gonophores, vial 232765; 1 colony, 7 mm high, without gonophores, vial
234099. –Isla Baltra, navy dock, collected April 2016 from fouling plate
deployed 15 January 2016, 3 colony fragments, up to 3.5 mm high, without
gonophores and 1 colony, 1 mm high, without gonophores, both sets of
Baltra material coll. K. Larson, vials 234198 and 232869 respectively.
Remarks.—These hydroids generally corresponded with Fraser’s (1938a)
brief original account of Eudendrium breve from Charles Island (Isla
Floreana), Galápagos. The species has also been reported from Isla Española
in the archipelago (Calder et al. 2003). Unlike the original description of
Fraser’s hydroid, pedicels in our specimens were annulated at the base, and
several bore one or more branches rather than being completely stolonal.
They appear very close also to hydroids identified as the presumably
cosmopolitan E. capillare Alder, 1856 (type locality: Embleton Bay,
Northumberland, England) at other locations in the Pacific including
Enewetak Atoll, Marshall Islands (Cooke 1975), Sagami Bay, Japan (Hirohito
1988), and Hawaii (Calder 2010). As with E. capillare, our specimens lacked
complementary nematocysts in addition to small microbasic euryteles. If
the Pacific population of hydroids assigned to E. capillare is indeed
identical with that of the Atlantic, Fraser’s E. breve is likely conspecific.
Knowledge of the gonophores, and especially those of female colonies, is
now considered critical in the characterization of species of Eudendrium
Ehrenberg, 1834. So too is knowledge of the cnidome. Eudendrium breve
constitutes a species inquirenda because type material was sterile and its
nematocyst complement has yet to be unequivocally established. Large
isorhizas in addition to microbasic euryteles were found in specimens
assigned with question to E. breve by Cooke (1975) from Enewetak Atoll.
Such nematocysts were not observed in material examined here.
Re-examination and redescription of type material (SBMNH 345383,
SBMNH 345384, SBMNH 346372) of the species, in collections at the Santa
Barbara Museum of Natural History, Santa Barbara, California, is needed.
Our specimens are assigned to E. breve with question given the inadequate
knowledge of the species, and with nothing but sterile material available in
the present collection.
In addition to records from the Galápagos and Enewetak Atoll,
Eudendrium breve has also been reported from Baja California (Fraser
1948).
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 31
Superorder Leptothecata Cornelius, 1992b
Order Statocysta Leclère, Schuchert, Cruaud, Couloux and Manuel, 2009
Family Cirrholoveniidae Bouillon, 1984
Cirrholovenia tetranema Kramp, 1959
Figure 3a
Cirrholovenia tetranema Kramp 1959: 253, figs. 17a, b [medusa].
Egmundella amirantensis Millard and Bouillon 1973: 40, figs. 5a–d [hydroid].
Lafoeina amirantensis.–Calder et al. 2003: 1180, fig. 5.
Material.—Isla Santa Cruz, Puerto Ayora, Franklin’s Bay, fouling community
on floats, epizoic on hydroid Nemalecium lighti, 27 February 2015, several
colonies, up to 2.5 mm high, without gonophores, coll. J. T. Carlton.
Remarks.—The hydroid known as Egmundella amirantensis Millard and
Bouillon, 1973 was shown, through life cycle studies by Migotto and Cabral
(2005), to be conspecific with the medusa Cirrholovenia tetranema Kramp,
1959. The latter name has nomenclatural priority and is accepted as valid
in WoRMS (Schuchert 2018).
The medusa of Cirrholovenia tetranema, originally described by Kramp
(1959) from the Solomon Islands (holotype) and from several other
localities in the Indo-Pacific, is now known from coastal and shelf waters
of the Atlantic, Pacific, and Indian oceans (Migotto and Cabral 2005). Based
on the known distribution of its medusa, Kramp (1968: 190) suspected that
C. tetranema was native to the Indo-Malayan region. The hydroid stage,
first described as E. amirantensis from Amirante, Seychelles (Millard and
Bouillon 1973), is also taken to be circumglobal in tropical and warm
temperate waters (Migotto and Cabral 2005). Other hydroids are a
common substrate of the species, although colonies have also been found
on bryozoans, macroalgae, and rocks.
Hydroids of this cryptogenic species have been reported earlier from the
Galápagos at Isla Daphne Chica, Isla Española, Isla Santa Cruz, and Isla
Isabela (Calder et al. 2003, as Lafoeina amirantensis).
Family Eucheilotidae Bouillon, 1984
Eucheilota sp.
Figure 3b
Material.—Isla Santa Cruz, Puerto Ayora, Franklin’s Bay, 27 April 2016,
on leg of spider crab Teleophrys cristulipes, coll. J. T. Carlton, JJM Hyd. 13.
Remarks.—The shallow hydrothecal vestiges of this hydroid superficially
resemble those of haleciids. However, in having a filmy curtain of perisarc
hanging down over the hydrophores, it corresponds instead with accounts
of various species of Eucheilota McCrady, 1859 by Werner (1968), Russell
(1970), Cornelius (1995a), Altuna (2008, 2009), and others. In species of
that genus, diaphanous hydrothecae resembling those of Aequorea Péron and
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 32
Figure 3. Lepthothecata: families Cirrholoveniidae, Eucheilotidae, Clytiidae, and Obeliidae.
a, Cirrholovenia tetranema, part of colony, with a hydrotheca and a nematotheca, Isla Santa
Cruz, Franklin’s Bay, scale equals 0.05 mm. b, Eucheilota sp., part of colony, with collapsed
wall of hydrotheca, Isla Santa Cruz, Puerto Ayora, Franklin’s Bay, JJM Hyd. 13, scale equals
0.1 mm. c, Clytia elongata, hydrotheca and distal end of pedicel, Isla Santa Cruz, Franklin’s
Bay, JJM Hyd. 16, scale equals 0.1 mm. d, Clytia linearis, hydrotheca and distal end of pedicel,
Isla Baltra, navy dock, SERC #232841, scale equals 0.2 mm. e, Clytia obliqua, hydrotheca and
distal end of pedicel, Isla Santa Cruz, Puerto Ayora, main passenger dock, JJM Hyd. 2, scale
equals 0.1 mm. f, Clytia thornelyi, hydrotheca and distal end of pedicel, Isla Santa Cruz, Franklin’s
Bay, JJM Hyd. 11, scale equals 0.1 mm. g, Obelia dichotoma, part of colony, with renovated
pedicel and hydrotheca, Isla Santa Cruz, Franklin’s Bay, fouling community on floats, scale
equals 0.1 mm. h, Obelia oxydentata, hydrotheca, Isla Santa Cruz, Franklin’s Bay, fouling
community on floats, scale equals 0.1 mm. i, Obelia oxydentata, part of hydrocaulus, with a
gonotheca, Isla Santa Cruz, Franklin’s Bay, fouling community on floats, scale equals 0.1 mm.
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 33
Lesueur, 1810 collapse as hydranths develop, leaving a wrinkled skirt of
perisarc hanging from the hydrothecal bases. The presence of punctae
above a basal diaphragm reinforces the impression of a haleciid. Our
hydroid may be referable to Eucheilota comata (Bigelow, 1909), the medusa
stage of which occurs in the tropical eastern Pacific, but definitive
identification is impossible in the absence of life cycle or genetic information.
Reduction of the hydrotheca accompanying growth of the hydranth also
occurs in several other species of leptothecate genera including Eutonina
Hartlaub, 1897, Eirene Eschscholtz, 1829, and Eutima McCrady, 1859.
In some works, Eucheilota and Eucheilotidae Bouillon, 1984 have been
included in Lovenellidae Russell, 1953. Bouillon (1984) and Cornelius
(1995a), among others, are followed here in recognizing Eucheilotidae as a
distinct family. The hydroid stages of eucheilotids, where known, are much
different morphologically from those of lovenellids (see Cornelius 1995a),
evidence that these families are distinct. Molecular studies (e.g. Leclère et
al. 2009; Maronna et al. 2016) that have explicitly or implicitly sunk
Eucheilotidae in the synonymy of Lovenellidae have misinterpreted
relationships of the two because certain included species were assigned to
the wrong genus. For presumed relationships of these families to be based
on sound evidence, genetic comparisons of the type species of their type
genera, Eucheilota and Lovenella Hincks, 1868 (Eucheilota ventricularis
McCrady, 1859 and Campanularia clausa Lovén, 1836, respectively), are
warranted.
No hydroids resembling Eucheilota sp. have been reported before from
the Galápagos.
Family Clytiidae Cockerell, 1911
Clytia elongata Marktanner-Turneretscher, 1890
Figure 3c
?Clytia elongata Marktanner-Turneretscher 1890: 215, pl. 3, fig. 11.
Material.—All but the last are specimens from fouling plates retrieved
April 2016 which had been deployed at Franklin’s Bay, Puerto Ayora, Isla
Santa Cruz, 27 February 2015, coll. K. Larson: 5 colony fragments, up to 4 mm
high, without gonophores, vial 234138; 5 colony fragments, up to 6 mm
high, without gonophores, vial 234236; 1 colony fragment, 3.5 mm high,
without gonophores, vial 234237; 1 colony fragment, 2 mm high, without
gonophores, vial 234921; 1 colony, 2.5 mm high, without gonophores, vial
232798. –Isla Santa Cruz, Puerto Ayora, Franklin’s Bay, epizoic on bryozoan
Amathia verticillata, 28 April 2016, 3 colony fragments, up to 4 mm high,
without gonophores, coll. K. Collins, JJM Hyd. 16.
Remarks.—A rare and poorly known species, Clytia elongata Marktanner-
Turneretscher, 1890 is nevertheless distinctive in the morphology of its
trophosome. As the specific name implies, its hydrothecae are deep and
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 34
slender. Also noteworthy are the low, rounded cusps on the hydrothecal rim.
While thereby resembling C. noliformis (McCrady, 1859) and C. thornelyi
(Nutting, 1927), hydrothecae of C. elongata are much deeper and more
cylindrical than in either of those species. Meanwhile, marginal cusps are
not truncated as in C. macrotheca (Perkins, 1908) and C. reloncavia Galea
and Schories, 2012. Gonophores and gonothecae of the species have yet to
be described, and none were observed here. Specimens from the Galápagos
corresponded closely in both shape and size (Figure 3c) with the original
account and illustration of the hydroid by Marktanner-Turneretscher
(1890) and with a subsequent overview of the species by Ralph (1957).
Clytia elongata, a probable introduction to the tropical eastern Pacific, is
previously known only from the western Pacific. Originally described from
Auckland, New Zealand, it has been reported elsewhere from New South
Wales, Australia (Ritchie 1911) and Cook Strait, New Zealand (Vervoort
and Watson 2003). Rees and Thursfield (1965) re-examined Ritchie’s
Australian specimens and found that they “…agree well with the figure
given by Marktanner-Turneretscher…”. By contrast, Vervoort and Watson
expressed uncertainty that specimens examined by them from Cook Strait
were the same species. In their illustration of the hydrotheca, marginal cusps
are more deeply incised than shown by Marktanner-Turneretscher, and the
hydrothecae are much larger. Those characters also differ from specimens
examined here. Clytia elongata Warren, 1908, a name applied to a different
species from Natal, South Africa, is an invalid junior primary homonym.
That binomen has been replaced by the name C. warreni Stechow, 1919.
Hydroids of Clytia elongata from the Galápagos were found on Amathia
verticillata, a ctenostome bryozoan that is also non-native to the archipelago
(McCann et al. 2015).
Clytia linearis (Thornely, 1900)
Figure 3d
Obelia linearis Thornely 1900: 453, pl. 44, fig. 6.
Clytia acutidentata Fraser 1938a: 28, pl. 7, figs. 29a, b. –Calder et al. 2003: 1210.
?Clytia carinadentata Fraser 1938a: 29, pl. 7, fig. 30. –Calder et al. 2003: 1210.
Clytia linearis.–Calder et al. 2003: 1202.
Material.—Specimens collected April 2016 from fouling plates deployed at
the Isla Baltra navy dock 15 January 2016, coll. K. Larson: 5 fragments, up
to 7 mm high, without gonothecae, vial 232841; 1 colony fragment, 7 mm
high, without gonothecae, vial 233083; 4 colony fragments, up to 4 mm
high, without gonothecae, vial 232880; 4 colony fragments, up to 6 mm
high, without gonothecae, vial 232867.
Remarks.—These hydroids correspond with Clytia linearis (Thornely,
1900) in having a keel-like perisarcal thickening extending from the apex
of each pointed marginal cusp downwards onto the distal wall of the
hydrotheca. This thickening, on the inner surface of the hydrotheca,
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 35
appears microscopically as a distinctive vertical line. The cusps and distal
end of the hydrotheca are also pleated in cross-section. Fully-developed
colonies usually exhibit sympodial growth. The taxonomy and nomenclature
of the species have been reviewed earlier (Calder 1991a), and its life cycle
was described by Lindner and Migotto (2002).
Clytia linearis, taken to be circumglobal in tropical and subtropical
waters (Medel and Vervoort 2000), was reported earlier from the
Galápagos by Calder et al. (2003). Included in the synonymy of the species
by Calder et al. (2009) were C. acutidentata Fraser, 1938a from the
Galápagos (Isla Floreana) and the Pacific coast of Mexico (Barra de Potosi),
C. carinadentata Fraser, 1938a from the Galápagos (Isla Isabela), and
Gonothyraea serialis Fraser, 1938a from the Pacific coast of Colombia
(Puerto Utria). Also included in the synonymy of C. linearis is Obelia
striata Clarke, 1907 from two locations in the tropical eastern Pacific (Rees
and Vervoort 1987; Calder 1991a). Although one of these records was
based on a colony from a trawl sample made at a depth of 2320 fm (4243 m),
the specimen was found on a pteropod likely picked up in much shallower
water. Another record of the species in the warm eastern Pacific is that of
Calder (1996) from Rocas Alijos, west of Baja California, Mexico.
While Clytia linearis is a substrate generalist (Calder 1991a, b), it is also
known to be frequent on shells of certain species of pteropods (Rees and
Vervoort 1987). Such an association might account, at least in part, for the
wide distribution of this hydroid. Alternatively, a circumglobal distribution
may indicate existence of a species complex under the name.
Clytia obliqua (Clarke, 1907)
Figure 3e
Campanularia (?) obliqua Clarke, 1907: 9, pl. 5, figs. 1–4.
Material.—Isla Santa Cruz, Puerto Ayora, Puerto Ayora dock, 25 April
2016, on stem of the hydroid Halopteris alternata, 1 colony, 2 mm high,
without gonophores, coll. J.J. Mallinson, JJM Hyd. 2.
Remarks.— In the morphology of its trophosome, the hydroid examined
here corresponds with species from the Indo-Pacific region that have been
identified as Clytia gracilis (M. Sars, 1850) (e.g. Gibbons and Ryland 1989;
Schuchert 2003), and as C. warreni Stechow, 1919 (e.g. Millard 1975;
Watson 2000). The type localities of those two species are Lofoten,
Norway, and Algoa Bay, South Africa, respectively. More likely, hydroids
from the Galápagos are conspecific with the morphologically similar
Campanularia (?) obliqua Clarke, 1907, originally described from Isla
Perico, Pánama. Clarke’s species is referable to Clytia, as first suggested by
Fraser (1936) and repeated later by Hirohito (1995). In an earlier work
(Calder 1991a), Clytia obliqua was included in the synonymy of C. linearis
(Thornely, 1900), but we regard them as distinct because of differences in
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 36
the morphology of their marginal cusps. In C. obliqua, there are no keel-like
thickenings of perisarc on the inner edge of each cusp as in C. linearis.
A degree of uncertainty in our identification arises because species of the
genus Clytia Lamouroux, 1812 are often inadequately distinguished and in
need of revision. Identification of our specimens is also hindered by the
absence of gonothecae.
Clytia obliqua has been reported from Japan (e.g. Fraser 1936; Yamada
1959; Hirohito 1995) and from California (Fraser 1948) in addition to the
type locality of Pánama. Hirohito expressed uncertainty whether hydroids
from Japan were actually conspecific with those reported by Fraser from
the eastern Pacific.
Clytia thornelyi (Nutting, 1927), comb. nov.
Figure 3f
Obelia thornelyi Nutting 1927: 202.
Material.—Isla Baltra, navy dock, collected April 2016 from fouling plate
deployed 15 January 2016, 10 colony fragments, up to 20 mm high, with
gonothecae, coll. K. Larson, vial 233083. –Isla Santa Cruz, Puerto Ayora,
Franklin’s Bay, fouling community on a pontoon, 27 April 2016, 6 colony
fragments, up to 5 mm high, without gonophores, coll. J. Geller, JJM Hyd. 11.
Remarks.—These specimens corresponded with accounts of Clytia latitheca
Millard and Bouillon, 1973, a distinctive clytiid hydroid originally described
from the Seychelles. The species is unusual in having hydrothecae with
strongly flaring hydrothecal walls, resembling a shallow funnel. While
hydrothecae somewhat resemble those of the Atlantic C. noliformis
(McCrady, 1859), they differ in having a thin diaphragm and in lacking a
distinct subhydrothecal spherule. Well-developed, fertile colonies were
found on fouling plates immersed at the Baltra navy dock (SERC 233083).
Gonothecae were paddle-shaped in lateral view, with smooth walls and a
truncate distal end.
As for Clytia latitheca, it has been considered identical with a hydroid
from Papua New Guinea identified by Thornely (1900) as Obelia serrulata
(Bale, 1888) (see Kirkendale and Calder 2003). Working on specimens from
the Philippines, Nutting (1927) justifiably argued that Thornely’s identification
was incorrect and recognized her hydroid as a new species, O. thornelyi.
Clytia latitheca has also been regarded as a junior synonym of C. stolonifera
Blackburn, 1938, an Australian species (Watson 2005). The senior synonym
and valid name of the species is therefore O. thornelyi, here assigned to
Clytia. While the specific name should have been spelled thornelyae, in
recognition of Laura Roscoe Thornely (1860–1951), the original spelling is
to be maintained (ICZN Art. 32.3; Brandon-Jones et al. 2007).
Clytia thornelyi has not been reported before from the Galápagos.
Although still a relatively obscure species, it appears to be widespread, with
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 37
scattered records from the tropical and subtropical western Atlantic (e.g.
Calder and Kirkendale 2005, as C. stolonifera; Oliveira et al. 2016, as
C. stolonifera), the west and central Pacific (e.g. Thornely 1900, as Obelia
serrulata; Nutting 1927, as O. thornelyi; Kirkendale and Calder 2003, as
C. latitheca; Di Camillo et al. 2008, as C. latitheca; Carlton and Eldredge 2009,
as C. latitheca) and Indian (e.g. Millard and Bouillon 1973, as C. latitheca)
oceans. We suggest that this species is a likely introduction to the Galápagos
from either the western Pacific or the western Atlantic Ocean.
Family Obeliidae Haeckel, 1879
Obelia dichotoma (Linnaeus, 1758)
Figure 3g
Sertularia dichotoma Linnaeus 1758: 812.
Obelia dichotoma.–Fraser 1938a: 36; 1938b: 133. –Calder et al. 2003: 1202. –Hickman 2008: 130,
three unnumbered figs.
Material.—Isla Santa Cruz, Puerto Ayora, Franklin’s Bay, fouling community
on floats, epizoic on Nemalecium lighti, 1 colony, 5 mm high, without
gonothecae, 27 February 2015, coll. J. T. Carlton. –Isla Santa Cruz, Puerto
Ayora, Franklin’s Bay, collected April 2016 from fouling plate deployed 27
February 2015, 1 colony fragment, 14 mm high, without gonophores, coll.
K. Larson, vial 234926. –Isla Baltra, navy dock, collected April 2016 from
fouling plate deployed 15 January 2016, 1 colony, 7 mm high, without
gonophores, coll. K. Larson, vial 232869.
Remarks.—It seems almost certain that a species complex exists under the
binomen Obelia dichotoma (Linnaeus, 1758). With a type locality on the
coast of southwest England (Cornelius 1975), the species has long been
considered abundant in many areas and virtually cosmopolitan in
distribution. It has been reported across the tropical and temperate Indo-
Pacific region (e.g. Fraser 1937; Millard 1975; Cooke 1977; Hirohito 1995;
Vervoort and Watson 2003; Watson 2005; Xu et al. 2014b), including the
Galápagos (Fraser 1938a, b; Calder et al. 2003; Hickman 2008). Affinities of
local populations remain to be determined, along with their origin. Of
note, Obelia dichotoma is considered a common component of marine
fouling assemblages (Woods Hole Oceanographic Institution 1952; Millard
1959; Standing 1976; Carlton and Eldredge 2009; Karlson and Osman
2012), having been reported on various substrates including test panels,
buoys, water pipes, and hulls of ships. Long-range transport by shipping is
therefore likely. It may thus be that open ocean, sublittoral populations of
what are now called O. dichotoma in the tropical eastern Pacific (including
the Galápagos) will prove to be an endemic species, whereas O. dichotoma
found in ports and harbors in the same region will be found to be members
of a global “harbor clade”, whose origin may, after centuries of global
shipping, be difficult to determine. Pending global genetic dissection of
this species, we regard O. dichotoma in the islands as cryptogenic.
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 38
Obelia oxydentata Stechow, 1914
Figure 3h, i
Obelia oxydentata Stechow 1914: 131, fig. 7.
Material.—Isla Santa Cruz, Tortuga Bay, epizoic on bryozoan Amathia
verticillata, 21 February 2015, 3 colony fragments, up to 6 cm high, with
gonothecae, coll. J. T. Carlton. –Isla Santa Cruz, Puerto Ayora, Franklin’s
Bay, fouling community on floats, 1 colony, 9 mm high, with gonothecae,
27 February 2015, coll. J. T. Carlton. –Isla Santa Cruz, Puerto Ayora,
Franklin’s Bay, 30 April 2016, 1 colony fragment, 5 mm high, without
gonophores, coll. K. Collins, JJM Hyd. 19.
Remarks.—No hydroids such as these, resembling the widely reported
Obelia bidentata Clark, 1875 (type locality: Long Island Sound, USA) and
especially the much less familiar O. oxydentata Stechow, 1914 (type
locality: St. Thomas, Virgin Islands), have been reported before from the
Galápagos Islands. Elsewhere in the eastern Pacific, hydroids similar to
these two species have been reported to the east from Isla Perico, Gulf of
Panama (Clarke, 1907, as Obelia (?) sp.), to the north in San Francisco Bay,
California (Fraser 1937, as O. bicuspidata; Mills et al. 2007, as O. bidentata),
and to the south in the fjords region of southern Chile (Galea et al. 2009, as
O. bidentata). Gibbons and Ryland (1989) remarked that hydroids from
Fiji resembled O. oxydentata (as illustrated by Hirohito 1969), but assigned
them instead to O. bidentata following Cornelius (1975). Gravier-Bonnet
(1999) applied the binomen O. oxydentata to similar hydroids from seagrass
beds in Madagascar. Specimens from the Galápagos are much the same as
those from Fiji and Madagascar, although gonothecae differ somewhat in
tapering distally rather than having a distinct terminal collar.
Over the last four decades, Obelia oxydentata has generally been taken to
be a synonym of O. bidentata (e.g. Cornelius 1975; Calder 1991a; WoRMS),
a supposedly cosmopolitan species (Medel and Vervoort 2000; Peña Cantero
and Gili 2006). Under that broad concept, however, O. bidentata likely
comprises a species complex (see Calder 2013, 2017). If hydroids identified
as O. bidentata across the warm Indo-Pacific region are indeed identical
with those of Clark (1875) from the cool-temperate western North Atlantic,
genetic confirmation is needed. Morphologically, Clark’s robust specimens
were as much as 15 cm high and had polysiphonic stems, unlike the
diminutive (< 1 cm high), monosiphonic colonies examined here. Instead,
our small specimens closely resemble accounts of O. oxydentata from
warm waters of the Caribbean (Stechow 1914) and Florida (Calder 2013).
Stechow (1914) included Clarke’s (1907) Obelia (?) sp. collected in 1904–1905
(before the 1914 opening of the Panama Canal) from the Gulf of Panama,
tropical eastern Pacific, in the synonymy of his new species O. oxydentata.
Unusual even in an era when global distributions of species were widely
accepted, Stechow was struck by finding the same hydroid species on both
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 39
sides of the Isthmus of Panama: “Die Auffindung dieser pacifischen Art
nunmehr hier auf der atlantischen Seite Amerikas ist außerordentlich
bemerkenswert” (The discovery of this Pacific species now, here on the
Atlantic side of America, is extraordinarily remarkable).
Obelia oxydentata is therefore known from the warm western Atlantic
(Stechow 1914; Calder 2013), the Indian Ocean (Gravier-Bonnet 1999)
and, very likely, Fiji (Gibbons and Ryland 1989). Until now, the sole
eastern Pacific record consisted of Clarke’s 1904–1905 material from Isla
Perico, an important Pacific Pánama port of the era. Once clearly
distinguished morphologically from O. bidentata, records of O. oxydentata are
likely to expand, perhaps significantly. At least some records of O. bidentata
or another of its many synonyms, O. bicuspidata Clark, 1875, from tropical
and warm temperate regions of the world, based on small, monosiphonic
hydroids (e.g. Millard and Bouillon 1973; Gibbons and Ryland 1989;
Calder 1991a, b; Migotto 1996; Kirkendale and Calder 2003; Calder and
Kirkendale 2005; Carlton and Eldredge 2009; Galea 2010), may represent
O. oxydentata.
While Obelia oxydentata has almost certainly been introduced to the
Galápagos, the source of eastern Pacific populations is unclear, as the
species may originate in either the tropical Indo-west Pacific or in the tropical
western Atlantic. Once many Obelia species can be assessed phylogenetically,
we predict that O. oxydentata will group with species endemic to one of
these two regions.
Order Macrocolonia Leclère, Schuchert, Cruaud, Couloux and Manuel, 2009
Family Haleciidae Hincks, 1868
Halecium labiatum Billard, 1933
Figure 4a, b
Halecium labiatum Billard, 1933: 21, figs. 8K–M.
Material.—Specimens collected April 2016 from fouling plates deployed at
the Isla Baltra navy dock, 15 January 2016, coll. K. Larson: 3 colony
fragments, up to 4 mm high, without gonophores, vial 232885; 7 colony
fragments, up to 4 mm high, with female gonophores, vial 234225; 4 colony
fragments, up to 7 mm high, without gonophores, specimens dry at some
point, vial 234190; 1 colony, 6 mm high, without gonophores, vial 232895;
6 colony fragments, up to 5 mm high, with female gonophores, vial 232882;
2 colony fragments, up to 6.5 mm high, without gonophores, vial 232875;
8 colony fragments, up to 9 mm high, with female gonophores, vial 232848;
3 colony fragments, up to 6 mm high, with female gonophores, vial 234201;
6 colony fragments, up to 5 mm high, without gonophores, vial 234222.
Remarks.—In being unfamiliar to us at first, these tiny specimens were
compared with accounts of all 140 species currently recognized in the
genus Halecium Oken, 1815. They are closest morphologically to a group of
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 40
Figure 4. Leptothecata: family Haleciidae. a, Halecium labiatum, part of hydrocaulus, with
hydrothecae, Isla Baltra, navy dock, SERC # 232882, scale equals 0.1 mm. b, Halecium
labiatum, part of colony with female gonotheca, Isla Baltra, navy dock, SERC # 232882, scale
equals 0.2 mm. c, Nemalecium lighti, part of a hydrocladium, with internodes and hydrothecae,
Isla Santa Cruz, Franklin’s Bay, fouling community on floats, scale equals 0.2 mm. d, Nemalecium
lighti, part of hydrocaulus, with a branch, hydrothecae, and a gonotheca, Isla Santa Cruz,
Franklin’s Bay, fouling community on floats, scale equals 0.5 mm.
about 40 species, including the type species H. halecinum (Linnaeus, 1758),
having female gonothecae of a fundamentally similar form (symmetry
bilateral; outline irregularly obovate in lateral view; aperture lateral rather
than terminal, with one or more gonophoral hydranths). Within that
group, characters of both trophosome and gonosome conformed closest
with those of H. labiatum Billard, 1933.
Halecium labiatum is very poorly known. The species was originally
described by Billard (1933) from material collected at a depth of 36–55 m
in the northern Gulf of Suez, Egypt. Subsequent published reports have
been from the Dahlak Archipelago in the southern Red Sea (Vervoort 1967),
the Gulf of Aden (Rees and Vervoort 1987), and (to where it may also be
introduced) Martinique, French Lesser Antilles (Galea and Ferry 2015).
Although seldom reported, it seems probable that this small hydroid has
on occasion been overlooked, misidentified, identified only to genus, or
simply ignored. At least some records of H. lankesterii (Bourne, 1890) are
likely to have been based on H. labiatum (in particular, see Millard 1968,
1975). Misidentifications of Bourne’s species have been noted earlier (Peña
Cantero and García Carrascosa 2002), although some reports of it from the
eastern Atlantic region were likely based on a species other than H. labiatum.
Halecium lankesterii is notable in being one of only a few species of the
genus having symbiotic zooxanthellae (Peña Cantero and García Carrascosa
2002). Such symbionts are absent in H. labiatum.
Colonies of H. labiatum are small, with few distinguishing characters
beyond the singular shape of their female gonothecae. As described best by
Galea and Ferry (2015), these structures are saccular in form, with a
bulging convex wall, a slightly sigmoid concave wall, and there provided
with a lateral aperture with a pair of adjoining hydrothecae towards the
distal end, a prominent lip protruding over the aperture, and two defensive
hydranths. Gonothecae often occur in pairs, as was usually the case in our
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 41
Figure 5. Photographs of hydroids from life. a, ?Bougainvillia sp., part of colony with a hydranth, Isla Santa Cruz, Puerto Ayora,
main passenger dock, JJM Hyd. 3. b, Nemalecium lighti, colonies hanging from underside of a boat, Isla Santa Cruz, Puerto Ayora,
Franklin’s Bay, JJM Hyd. 10. c, Nemalecium lighti, hydranths of colonies fouling same boat, Isla Santa Cruz, Puerto Ayora, Franklin’s
Bay, JJM Hyd. 10. Nematodactyls of the species are not distinct in the photograph but were visible under a microscope. d, Halopteris
alternata, two colonies, Isla Santa Cruz, Puerto Ayora, main passenger dock, JJM Hyd. 1. Photographs by J.J. Mallinson.
specimens. Material examined by Galea and Ferry had 1–2 large eggs per
gonotheca, while the usual number in ours was three. Curiously, all fertile
colonies examined here were female.
This species is recorded for the first time anywhere in the Pacific Ocean.
Specimens were quite frequent, and well-developed, on fouling plates
immersed at the Baltra navy dock. Transport to the Galápagos by shipping
therefore seems probable, given the location, but the source of these
populations is obscure.
Nemalecium lighti (Hargitt, 1924)
Figures 4c, d; 5b, c
Halecium lighti Hargitt 1924: 489, pl. 4, fig. 13.
Nemalecium lighti.–Hickman 2008: 129, three unnumbered figs. –Banks et al. 2009, pp. 51, 53,
56, 59.
Material.—Isla Santa Cruz, Puerto Ayora, Franklin’s Bay, fouling community
on floats, 27 February 2015, 10 colony fragments, up to 2.5 cm high, with
gonophores, coll. J.T. Carlton. –Isla Santa Cruz, Puerto Ayora, Franklin’s
Bay, collected April 2016 from fouling plate deployed 27 February 2015,
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 42
2 colony fragments, up to 5 mm high, without gonophores, coll. K. Larson,
vial 232925. –Isla Santa Cruz, Puerto Ayora, main passenger dock, collected
April 2016 from fouling plate deployed 27 February 2015, 6 colony fragments,
up to 7 mm high, without gonophores, coll. K. Larson, vial 234261. –Isla
Santa Cruz, Puerto Ayora, Franklin’s Bay, collected April 2016 from fouling
plate deployed 27 February 2015, 2 colony fragments, up to 4 mm high,
without gonophores, coll. K. Larson, vial 234148. –Isla Santa Cruz, Puerto
Ayora, Franklin’s Bay, on mooring rope, 27 April 2016, 8 colony fragments,
up to 2.5 cm high, without gonophores, coll. J.J. Mallinson, JJM Hyd. 10.
Remarks.—Originally described from Puerto Galera Bay, Mindoro,
Philippines (Hargitt 1924), Nemalecium lighti was first reported in the
eastern Pacific from the Galápagos based upon 2005–2007 collections from
Islas Wolf, Darwin, and Marchena (Banks et al. 2009; see also Hickman
2008, for color illustrations).
The species has been reported elsewhere in both the Indo-west Pacific
region (e.g. Pennycuik 1959, as Halecium sessile Norman, 1867; Gravier-
Bonnet and Migotto 2000; Kirkendale and Calder 2003; Galea et al. 2012)
and the warm western Atlantic (e.g. Calder 1991a; Migotto 1996; Galea
2008; Oliveira et al. 2016). A second species of Nemalecium Bouillon, 1986,
N. gracile, was recently described from the Caribbean region (Galea et al.
2012). It is uncertain how many records of N. lighti from the Atlantic
might be referable to N. gracile instead. Meanwhile, Gravier-Bonnet and
Migotto (2000) and Galea et al. (2012) have noted that additional species of
Nemalecium may exist in the Indo-Pacific. Colonies examined here were
particularly noteworthy for the great length and slenderness of their
gonothecae. Some of them measured more than 2.5 mm from base to apex,
while being less than 0.5 mm in diameter (Figure 4d). The largest ones
included in a table by Galea et al. 2012 (those of N. cf. lighti from Brazil,
described by Migotto 1996), were 1.9 mm long and 0.8 mm in diameter.
Additional taxonomic investigations on the population in the Galápagos
are warranted. We tentatively assign an introduced status to N. lighti, with
possible origins in either the Indo-west Pacific or the western Atlantic.
Although traditionally assigned to Haleciidae, and so classified here,
Nemalecium lighti now appears misplaced in that family. Evidence from
molecular data indicates that the species is not a haleciid, and Maronna et
al. (2016) included it in a new leptothecate suborder, Plumupheniida. As
noted by them, research is needed to better resolve its systematic position.
Family Sertulariidae Lamouroux, 1812
Amphisbetia distans (Lamouroux, 1816), comb. nov.
Figure 6a, b
Dynamena distans Lamouroux 1816: 180, pl. 5, figs. 1a, B.
Sertularia stookeyi.–Fraser 1938: 55; 1948: 250.
Tridentata distans.–Calder et al. 2003: 1203.
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 43
Figure 6. Leptothecata: family Sertulariidae. a, Amphisbetia distans, part of colony, with three
hydrothecal pairs, Isla Bartolomé, JJM Hyd. 17, scale equals 0.2 mm. b, Amphisbetia distans,
part of colony, with two hydrothecal pairs, Isla Bartolomé, JJM Hyd. 17, scale equals 0.1 mm.
c, Tridentata turbinata, part of colony, with two hydrothecal pairs, Isla Santa Cruz, Puerto
Ayora, main passenger dock, JJM Hyd. 21, scale equals 0.25 mm.
Material.—Isla Bartolomé, 12.2 m, 29 April 2016, on large red tunicate
Halocynthia dumosa, 6 colony fragments, up to 1 cm high, without
gonophores, coll. G. Lambert, JJM Hyd. 17.
Remarks.—Dynamena distans Lamouroux, 1816, also known as Sertularia
distans, Tridentata distans, and Sertularia stookeyi Nutting, 1904, among
others (see synonymy in Medel and Vervoort 1998), is assigned here to
Amphisbetia L. Agassiz, 1862 on the basis of molecular evidence. Phylograms
in Moura et al. (2011) and Maronna et al. (2016) reveal that the species is
much closer genetically to Sertularia operculata Linnaeus, 1758 (type
species of Amphisbetia L. Agassiz, 1862) than to either Sertularia argentea
Linnaeus, 1758 (type species of Sertularia Linnaeus, 1758) or Sertularia
perpusilla Stechow, 1919 (type species of Tridentata Stechow, 1920). In terms
of morphology, gonothecae of the species resemble those of S. operculata
more closely than those of S. perpusilla in being ovate with smooth walls
instead of barrel-shaped with transverse ribs (Calder 2013). They are also
much different from those of S. argentea, particularly in lacking one or
more disto-lateral horns.
Originally reported from pelagic Sargassum and other floating objects in
the Atlantic Ocean (Lamouroux 1816), Amphisbetia distans is believed to
be circumglobal in distribution. A species with distinctively tiny and
slender hydrothecae, it appears to be common in the Galápagos. To date,
A. distans has been reported from the following islands in the archipelago:
Wolf (Fraser 1938a, as Sertularia stookeyi; Calder et al. 2003, as Tridentata
distans), Isabela (Fraser 1938a, as S. stookeyi), Seymour Norte (Fraser 1948,
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 44
as S. stookeyi), San Cristóbal (Fraser 1948, as S. stookeyi), and Bartolomé
(this study). Moura et al. (2011) suggested that cryptic species may exist
within Sertularia distans (=A. distans), at least in the Atlantic Ocean.
Detailed accounts of this species have been given earlier (Calder 1991a,
2013, as Tridentata distans; Cornelius 1995b, as T. distans; Hirohito 1995,
as Sertularia distans; Medel and Vervoort 1998, as S. distans).
Tridentata turbinata (Lamouroux, 1816)
Figure 6c
Dynamena turbinata Lamouroux 1816: 180.
Tridentata turbinata.–Calder et al. 2003: 1194, fig. 16.–Hickman 2008: 132, three unnumbered figs.
Material.—Isla Baltra, 28 April 2016, on a weight, 5 colony fragments, up to
8 mm high, without gonophores, coll. J.J. Mallinson, JJM Hyd. 23. –Isla Santa
Cruz, Puerto Ayora, Puerto Ayora dock, 2 May 2016, 7 colony fragments,
up to 1.6 cm high, without gonophores, coll. J.J. Mallinson, JJM Hyd. 21.
Remarks.—As reflected in an exhaustive synonymy list of this species by
Medel and Vervoort (1998, as Sertularia turbinata), Tridentata turbinata
(Lamouroux, 1816) has usually been assigned to Sertularia Linnaeus, 1758
under the binomen S. turbinata. Molecular data compiled by Maronna et al.
(2016) reveal that it is genetically remote from Sertularia argentea Linnaeus,
1758, type species of the Linnean genus, and that it is phylogenetically
closest to S. perpusilla Stechow, 1919, type species of Tridentata Stechow,
1920. Tridentata turbinata and T. perpusilla, together with T. marginata
(Kirchenpauer, 1864) and T. tumida (Allman, 1877), cluster as a monophyletic
group in the phylograms of Maronna et al. Morphological evidence exists
as well for recognition of Tridentata (Calder 1991a, 2013), particularly in
the shape of the gonothecae as described below, and T. turbinata is upheld
here as the valid name of this species.
Fertile colonies of T. turbinata have seldom been observed (Calder 2013;
Galea and Ferry 2015, as S. turbinata), and hydroids examined here were
also sterile. As described by Vervoort (1959, as S. turbinata), Millard (1975,
as S. turbinata), Hirohito (1995, as S. turbinata), Galea and Ferry (2015, as
S. turbinata), and Humara-Gil and Cruz-Gómez (2018, as Tridentata
turbinata), however, gonothecae are similar in morphology to those of
T. perpusilla and T. marginata in being barrel-shaped with about 5–8
prominent transverse ribs. The aperture is terminal and wide in diameter.
Gonothecae of the closely related T. tumida have yet to be reliably described.
Originally discovered in “Australasia” (Lamouroux 1816), T. turbinata is
now considered circumglobal in tropical and subtropical waters. The
species has been identified previously from the Galápagos at Isla Tortuga
(Calder et al. 2003). Hickman (2008) also reported it from the islands, but
did not specify a location.
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 45
Figure 7. Leptothecata: families Kirchenpaueriidae and Halopterididae. a, Ventromma halecioides,
part of hydrocaulus, with two hydrocladia, Isla Santa Cruz, Puerto Ayora, main passenger dock,
JJM Hyd. 7, scale equals 0.20 mm. b, Ventromma halecioides, part of hydrocaulus, with a
hydrocladium, nematothecae, and a hydrotheca, Isla Santa Cruz, Puerto Ayora, main passenger
dock, JJM Hyd. 7, scale equals 0.1 mm. c, Halopteris alternata, part of hydrocaulus, with a
hydrocladium, nematothecae, and three hydrothecae, Isla Santa Cruz, Puerto Ayora, main
passenger dock, JJM Hyd. 1, scale equals 0.2 mm. d, Halopteris alternata, part of a hydrocladium,
with nematothecae and a hydrotheca, Isla Santa Cruz, Puerto Ayora, main passenger dock, JJM
Hyd. 1, scale equals 0.1 mm.
Family Kirchenpaueriidae Stechow, 1921
Ventromma halecioides (Alder, 1859)
Figure 7a, b
Plumularia halecioides Alder 1859: 353, pl. 12, figs. 1–5.
Plumularia inermis.–Fraser 1938a: 64, p. 15, figs. 74a, b.
Ventromma halecioides.–Calder et al. 2003: 1200.
Material.—Specimens collected April 2016 from fouling plates deployed at
Franklin’s Bay, Puerto Ayora, Isla Santa Cruz, 27 February 2015, coll. K.
Larson: 2 colony fragments, up to 6 mm high, without gonophores, vial
234138; 1 colony, 3 mm high, without gonophores, vial 234266; 1 colony, 6 mm
high, without gonophores, vial 234236; 2 colony fragments, up to 7 mm
high, without gonophores, vial 234244; 1 colony fragment, 11.5 mm high,
without gonophores, vial 234245; 3 colony fragments, up to 13 mm high,
without gonophores, vial 233108. –Specimens from fouling plates deployed
at the main passenger dock, Puerto Ayora, Isla Santa Cruz, 27 February
2015, coll. K. Larson: 2 colony fragments, up to 7 mm high, without
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 46
gonophores, vial 234261; 3 colony fragments, up to 13 mm high, without
gonophores, vial 232956; 2 colony fragments, up to 6 mm high, without
gonophores, vial 234288; 1 colony fragment, 7 mm high, without
gonophores, vial 233137; 8 colony fragments, up to 27 mm high, without
gonophores, vial 310276; 1 colony fragment, 9 mm high, without
gonophores, vial 234122. –Isla Santa Cruz, Puerto Ayora, main passenger
dock, collected April 2016 from fouling cage (?) deployed 27 February
2015, 1 colony fragment, 6 mm high, without gonophores, coll. K. Larson,
vial 232796. –Isla Santa Cruz, Puerto Ayora, main passenger dock, collected
April 2016 from fouling plate deployed 15 January 2016, 2 colony fragments,
up to 11 mm high, without gonophores, coll. K. Larson, vial 234056. –Isla
Santa Cruz, Puerto Ayora, Puerto Ayora dock, 27 February 2015, on fouling
panel rope, 6 colony fragments, up to 2.5 cm high, without gonophores,
coll. J.J. Mallinson, JJM Hyd. 7. –Isla Santa Cruz, Puerto Ayora, Puerto
Ayora dock, 25 April 2016, on fouling panel rope, 1 colony, 2.4 cm high,
without gonophores, coll. J.J. Mallinson, JJM Hyd. 8. –Isla Santa Cruz,
Puerto Ayora, Puerto Ayora dock, 26 April 2016, 7 colony fragments, up to
3 cm high, one colony with a gonophore, coll. J.J. Mallinson, JJM Hyd. 7a.
Remarks.—Originally described as Plumularia halecioides by Alder (1859)
from the northeast coast of England, opinions currently differ over the
generic assignment of this species. Although no longer considered a species
of Plumularia Lamarck, 1816, it has been combined in some works with
Kirchenpaueria Jickeli, 1883, and in others with Ventromma Stechow,
1923. Morphological differences between the two genera are minor, with
nematophores being naked in Kirchenpaueria and protected by nematothecae
in Ventromma. More conclusively, molecular studies (Leclère et al. 2007;
Moura et al. 2008; Peña Cantero et al. 2010; Maronna et al. 2016) have
demonstrated that P. halecioides, the type species of Ventromma, is highly
divergent genetically from Kirchenpaueria pinnata (Linnaeus, 1758), type
species of Kirchenpaueria. Support for recognition of the genus Ventromma
is most recently provided by 16S sequence data showing Kirchenpaueria
halecioides forming a sister clade to other taxa of Kirchenpaueriidae
(Moura et al. 2018). We therefore adopt Ventromma halecioides as the
valid name of the species.
Although confirmation is needed, hydroids of V. halecioides are currently
believed to be circumglobal in warm-temperate and tropical waters (Calder
2013). The species has been reported earlier from the Galápagos at Isla
Fernandina (Calder et al. 2003). Another record, from Isla Floreana (Fraser
1938a, as Plumularia inermis Nutting, 1900), is likely based on a
misidentification. While P. inermis is a junior subjective synonym of
V. halecioides, Fraser’s material differs in having homomerously segmented
hydrocladia. Moreover, gonothecae were elongated and obovate with smooth
walls and with a rounded distal end instead of being deep cone-shaped with
distinct transverse ridges and with a truncate distal end, as in V. halecioides.
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 47
Clarke (1907) identified a hydroid from bathyal waters (1063 m) off the
Pacific coast of Pánama as Plumularia helleri Hincks, 1872, a name now
included in the synonymy of Kirchenpaueria pinnata (Linnaeus, 1758).
Clarke’s illustration shows that his species, a kirchenpaueriid with
nematothecae, is referable instead to Ventromma, but not to V. halecioides
or any other known species of the genus. While its hydrocladia are
heteromerously segmented, the adcauline wall of the hydrotheca is about
one-third free (Clarke 1907: pl. 15, figs. 1–6). This deep-water species,
deemed herein to be new, warrants redescription and naming. Material to
serve as a holotype exists at the NMNH (USNM 29620, as Plumularia helleri,
R/V Albatross Station Number 4622, United States Fish Commission
Eastern Pacific Expedition, centroid latitude 6.5167, centroid longitude
−81.7333, south of Coiba Island, Pánama, 21 October 1904).
Ventromma halecioides, cryptogenic in the islands, is frequent in areas of
quiet, shallow water (Calder 2013), as with the dock areas sampled in
Puerto Ayora. It is known to be a component of certain fouling communities,
occurring on ships and buoys (Woods Hole Oceanographic Institution
1952, as Plumularia halecioides) and in ports (Cornelius 1992b).
Family Halopterididae Millard, 1962
Halopteris alternata (Nutting, 1900)
Figures 5d; 7c, d
Plumularia alternata Nutting 1900: 62, pl. 4, figs.1, 2.
Not Plumularia alternata.–Fraser 1938a: 62, pl. 14, figs. 71a, b.
Material.—Specimens collected April 2016 from fouling plates deployed at
Franklin’s Bay, Puerto Ayora, Isla Santa Cruz, 27 February 2015, coll. K.
Larson: 3 colony fragments, up to 15 mm high, without gonophores, vial
234130; 1 colony, 8 mm high, with gonophores, vial 234154; 6 colony
fragments, up to 9 mm high, without gonophores, vial 232798; 2 colony
fragments, up to 4.5 mm high, without gonophores, vial 232812; 5 colony
fragments, up to 18 mm high, without gonophores, vial 232823; 9 colony
fragments, up to 15 mm high, without gonophores, vial 234265; 6 colony
fragments, up to 18 mm high, without gonophores, vial 232928. –Isla Santa
Cruz, Puerto Ayora, Franklin’s Bay, 30 April 2016, on fouling panel, 5 colony
fragments, up to 9 mm high, without gonophores, coll. G. Ruiz, JJM Hyd.
18a. –Specimens collected April 2016 from fouling plates deployed 27
February 2015 at main passenger dock, Puerto Ayora, Isla Santa Cruz, coll.
K. Larson: 2 colony fragments, up to 8 mm high, without gonophores, vial
232790; 4 colony fragments, up to 9 mm high, without gonophores, vial
233075; same, collections made April 2016 from fouling panels deployed at
main passenger dock but on 15 January 2016: 2 colony fragments, up to 11 mm
high, without gonophores, vial 232746; 3 colony fragments, up to 10 mm high,
without gonophores, vial 233011; 1 colony fragment, 6 mm high, without
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 48
gonophores, vial 233028. –Isla Santa Cruz, Puerto Ayora, Puerto Ayora
dock, 25 April 2016, on fouling panel, 10 colony fragments, up to 18 mm high,
without gonophores, coll. L. McCann, JJM Hyd. 1. –Isla Santa Cruz, Puerto
Ayora, Puerto Ayora dock, 02 May 2016, on sponge, 7 colony fragments,
up to 13 mm high, without gonophores, coll. N de Voogd, JJM Hyd. 22.
Remarks.—In being referable to the genus Halopteris Allman, 1877, these
hydroids fall within the “H. diaphana” group of species recognized by
Schuchert (1997). Of that group, they most closely resemble H. alternata
(Nutting, 1900) from the tropical and subtropical Atlantic Ocean and are
assigned to that species. Unlike H. billardi (Vannucci, 1951), H. diaphana
(Heller, 1868), H. tenella (Verrill, 1873), H. platygonotheca Schuchert,
1997, and H. violae Calder et al., 2003 of that particular assemblage, axillar
nematothecae are present or often present above the cauline hydrothecae
in our material. They also differ from H. billardi in having monosiphonic
hydrocauli, from H. diaphana in having much coarser internodes on both
hydrocaulus and hydrocladia, from H. tenella in having unbranched
hydrocladia, and from H. violae in lacking disto-lateral nematothecae on
cauline internodes. Unlike in H. diaphana, H. tenella, and H. violae,
hydrocladial internodes are of two types only; short anematothecate
internodes are never present distal to a hydrothecate internode. Although
similar to hydroids identified as H. polymorpha (Billard, 1913), they differ
in lacking axillar nematothecae above hydrocladial hydrothecae.
Halopteris alternata was reported in the Galápagos from Isla Wolf and
Isla Floreana by Fraser (1938a, as Plumularia alternata), but Schuchert
(1997) believed that those records were based on a different, undetermined
species. Unlike the spindle-shaped gonothecae of H. alternata, as described
by Schuchert, those of colonies described by Fraser were in the shape of
curved cornucopiae.
Originally described from the Bahamas (Nutting 1900), the range of
H. alternata extends from North Carolina and Bermuda to Brazil in the
western Atlantic, and from the vicinity of Madeira, the Canary Islands, and
the Cape Verde Islands in the eastern Atlantic (Ansín Agís et al. 2001). It is
reported here as a probable introduction for the first time from the Galápagos
Islands. Earlier records of the species from various locations across the
Pacific Ocean are considered doubtful (Schuchert 1997). H. alternata is
widespread in the Caribbean (Calder and Kirkendale 2005) and may have
been transported into the eastern Pacific from the Caribbean region via the
Panama Canal.
Discussion
Constraining the detection of introduced hydroids in regions such as the
Galápagos Islands is the reported natural cosmopolitan, and especially
tropicopolitan, distribution of a great many species of shallow-water
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 49
hydroids, most or all of which, if not transported around the world by
centuries of shipping, may prove to be species complexes. This said, for
many marine taxa, the Central American Land Barrier has served to isolate
Caribbean and eastern Pacific biotas for millions of years (James 1991;
Hickman 2009), making it unlikely that the same species now naturally
occur on either side of the Isthmus of Panama. Global shipping since the
1500s has, however, served to disperse many marine invertebrates, algae,
and fishes across and between oceans (Carlton 2009) such that the
appearance of, for example, Caribbean or western Pacific hydroid species
in the Galápagos Islands would not be unexpected.
Regionally, the Panama Canal may have served as an important corridor
since 1914 for Caribbean hydroids entering the tropical eastern Pacific
Ocean (Cohen 2006). Although the freshwater Gatun Lake would appear to
be a barrier to the dispersal of marine species, shipping has nevertheless
likely transported many hydroid species from the Atlantic to the Pacific
(and vice-versa). Dormant stages exist in their life cycles that could survive
temporarily unfavourable environmental conditions encountered over the
short distance and travel time required in crossing through Pánama.
Perhaps more important, however, is the presence of both medusae and
polyp stages of hydrozoans in ships’ ballast water (Carlton and Geller 1993;
Smith et al. 1999, J. T. Carlton, personal observations), such that species
transported inside vessels would pass imperviously through the Panama
Canal and be released on the Central American Pacific coast.
We conservatively recognize here eight introduced and five cryptogenic
species of hydroids (Table 1). The introduced species are recognized through
their remarkable disjunct distributions, making natural distribution and
dispersal unlikely. The cryptogenic species are primarily so designated
because they may be members of world-wide species complexes, within
which endemic tropical eastern Pacific species may reside. To the species
treated here, we add one introduced species reported earlier (Calder et al.
2003) of either Caribbean or Indo-west Pacific origin, Clytia hummelincki
(Leloup, 1935), and one cryptogenic species of unknown origin, Pennaria
disticha Goldfuss, 1820. Calder et al. (2003) recorded additional species of
hydroids in the open ocean, sublittoral Galápagos fauna that were
previously known either from the Atlantic or the western Pacific, but
whose biogeography and taxonomy require further investigation.
Of the introduced species, two (Bougainvillia muscus and Halopteris
alternata) may be from the Atlantic Ocean, and two from the broad Indo-
Pacific theater (Halecium labiatum and Clytia elongata). The remaining
four (Clytia thornelyi, C. hummelincki, Obelia oxydentata, and Nemalecium
lighti) may originate from either the warm waters of the western Atlantic
or the western Pacific. Genetic analyses seeking centers of haplotype
diversity, phylogenetic analyses grouping sibling species, or both, may
Hydroids from fouling assemblages in the Galápagos Islands
Calder et al. (2019), Aquatic Invasions 14(1): 21–58, https://doi.org/10.3391/ai.2019.14.1.02 50
eventually point to the origins of these species. No introduced species
known only from the tropical eastern Atlantic have yet been detected in the
Galápagos.
The 2016 dates of first collection of seven of the hydroid species newly
added here as introductions or cryptogens to the Galápagos marine fauna
do not likely represent new invasions; that is, these records should not be
interpreted as part of a new wave of invasions now occurring in the
archipelago. Rather, there have been few historical investigations of the
biofouling communities in Galápagos ports and harbors (Carlton et al.
2019). While the present investigations (Carlton et al. 2019) thus form a
baseline of the diversity of these communities, we do not know when these
species first arrived. Given that vessels have been visiting the Galápagos
since the 1500s, we have little doubt that with further study, and with
resolution of the biogeography of many other species, the list of non-native
hydroids will grow considerably.
Finally, we note that the present 2015 and 2016 collections took place
during a strong El Niño episode (Stramma et al. 2016) in the equatorial
eastern Pacific. With no seasonal or long-term data available on the
diversity and distribution of hydroids in the Galápagos Archipelago, it is
difficult to interpret what effect these unusually warm seawater
temperatures may have had on the fauna. It may be that future studies will
be able to place the current collections in a broader temporal framework.
Acknowledgements
We are grateful to Ken Collins, Graham Edgar, Jonathan Geller, Gretchen Lambert, Linda
McCann, Mark Torchin, and Nicole de Voogd for providing some of the specimens examined
here. Horia R. Galea, Jeanette E. Watson, and an anonymous referee are sincerely thanked for
providing constructive reviews of the manuscript. Research funding, acknowledged with
gratitude, was provided by Galápagos Conservancy, Lindblad Expedition/National Geographic
Fund and The Leona M. and Harry B. Hemsley Charitable Trust. The Galápagos National Park
Directorate (GNPD), The Galápagos Biosecurity Agency (ABG), The Ecuadorian Navy and the
Oceanographic Institute of the Ecuadorian Navy (INOCAR) are thanked for their support in this
research. Parts of the study were also made possible by earlier financial support provided by the
Natural Sciences and Engineering Research Council of Canada, the Royal Ontario Museum, the
University of Toronto, and the United States National Science Foundation program Partnerships
for Enhancing Expertise in Taxonomy (PEET).
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Supplementary material
The following supplementary material is available for this article:
Table S1. Occurrences of Hydrozoa at sampling locations in the Galápagos Islands, 2001–2016.
This material is available as part of online article from:
http://www.aquaticinvasions.net/2019/Supplements/AI_2019_Calder_etal_Table_S1.xlsx
