Taxonomic review of the hydrothermal vent shrimp genera Rimicaris Williams and Rona and Chorocaris Martin and Hessler (Crustacea : Decapoda : Caridea : Alvinocarididae)

Abstract

A taxonomic review of the two genera of the family Alvinocarididae (Decapoda: Caridea), Rimicaris Williams and Rona, 1986 and Chorocaris Martin and Hessler 1990, is presented based on study of type materials and/or supplemental material from recent collections. Two species of Rimicaris, R. exoculata Williams and Rona 1986 and R. kairei Watabe and Hashimoto 2002, and three species of Chorocaris, C. chacei Williams and Rona 1986, C. vandoverae Martin and Hessler 1990, and C. paulexa Martin and Shank 2005, are recognized. All species are exclusively associated with deep-water hydrothermal community. Close relationship between the two genera is confirmed by morphological characters, but the monophyly of Chorocaris is not corroborated. An examination of a good series of material from the Mid-Atlantic Ridge shows that juveniles of Rimicaris exoculata can be arranged in four sequential ontogenetic stages based on morphology. A dramatic change occurs at the size of 7.0 to 9.0 mm in the carapace length. The synonymies of lorania concordia Vereshchaka 1996 and Rimicaris aurantiaca Martin, Signorovitch and Patel 1997 with Rimicaris exoculata, indicated from molecular evidence by Shank et al. (1998), are confirmed. Morphological differences between R. exoculata and R. kairei and those among C. chacei, C. vandoverae, and C. paulexa, are reassessed.

Full text

TAXONOMIC REVIEW OF THE HYDROTHERMAL VENT SHRIMP GENERA
RIMICARIS WILLIAMS & RONA AND CHOROCARIS MARTIN & HESSLER
(CRUSTACEA: DECAPODA: CARIDEA: ALVINOCARIDIDAE)
TOMOYUKI KOMAI
1
* AND MICHEL SEGONZAC
2
1
Natural History Museum and Institute, Chiba, 955-2 Aoba-cho, Chuo-ku, Chiba, 260-8682 Japan;
2
Ifremer, Centre de Brest, DEEP/Laboratoire Environnement profond, F-29280, Plouzane
´, France
ABSTRACT A taxonomic review of the two genera of the family Alvinocarididae (Decapoda: Caridea), Rimicaris Williams and
Rona, 1986 and Chorocaris Martin and Hessler 1990, is presented based on study of type materials and/or supplemental material
from recent collections. Two species of Rimicaris,R. exoculata Williams and Rona 1986 and R. kairei Watabe and Hashimoto
2002, and three species of Chorocaris,C. chacei Williams and Rona 1986, C. vandoverae Martin and Hessler 1990, and C. paulexa
Martin and Shank 2005, are recognized. All species are exclusively associated with deep-water hydrothermal community. Close
relationship between the two genera is confirmed by morphological characters, but the monophyly of Chorocaris is not corrob-
orated. An examination of a good series of material from the Mid-Atlantic Ridge shows that juveniles of Rimicaris exoculata can
be arranged in four sequential ontogenetic stages based on morphology. A dramatic change occurs at the size of 7.0 to 9.0 mm in
the carapace length. The synonymies of Iorania concordia Vereshchaka 1996 and Rimicaris aurantiaca Martin, Signorovitch &
Patel 1997 with Rimicaris exoculata, indicated from molecular evidence by Shank et al. (1998), are confirmed. Morphological
differences between R. exoculata and R. kairei and those among C. chacei,C. vandoverae, and C. paulexa, are reassessed.
KEY WORDS: Crustacea, Decapoda, Caridea, Alvinocarididae, Rimicaris,Chorocaris, taxonomy, hydrothermal vents
INTRODUCTION
Species of the caridean shrimp family Alvinocarididae exclu-
sively occur in reducing habitats in deepwater, (i.e., hydrother-
mal vents or cold water sulfide/hydrocarbonseeps. At present,
they are classified into 7 genera, including Alvinocaris Williams
and Chace 1982, Chorocaris Martin and Hessler 1990, Mir-
ocaris Vereshchaka 1997, Nautilocaris Komai and Segonzac
2004, Opaepele Williams and Dobbs 1995, Rimicaris Williams
and Rona 1986, and Shinkaicaris Komai and Segonzac 2005
(Komai & Segonzac 2003, Komai & Segonzac 2004, Komai &
Segonzac 2005, Martin & Haney 2005). Komai and Segonzac
(2003) did not recognize Mirocarididae, originally proposed
by Vereshchaka (1997a) to accommodate the genus Mirocaris,
because the presence of possible synapomorphies strongly
suggests that Mirocaris is subordinated in Alvinocarididae.
Rimicaris was originally established for two species discov-
ered from hydrothermally influenced vent field, TAG (Tans-
Atlantic Geotraverse) on the MAR (Mid-Atlantic Ridge),
Rimicaris exoculata Williams and Rona 1985 and R. chacei
Williams and Rona 1986 (Williams & Rona 1986). The former
was designated as the type species of the genus. Later, Martin
and Hessler (1990) described a new genus, Chorocaris, for a
new species C. vandoverae (the type species of the genus) from
hydrothermal vents along the Back-Arc Spreading Center in the
western Pacific, and transferred Rimicaris chacei to Chorocaris.
Martin and Christiansen (1995) described a new species,
Chorocaris fortunata, from Lucky Strike on the MAR, but this
species was later transferred to Mirocaris by Vereshchaka
(1997a). Martin et al. (1997) described a new taxon, Rimicaris
aurantiaca Martin, Signorovich and Patel 1997, as the second
representative of Rimicaris based on material from Snake Pit
vent field on the MAR, but the subsequent genetic studies
suggested that the taxon was founded from juvenile of R.
exoculata (Shank et al. 1998, Shank et al. 1999). Similarly, it
was indicated that the genus Iorania Vereshchaka 1996, and the
type species I. concordia Vereshchaka 1996, described from the
TAG, were founded on juveniles of R. exoculata. Hashimoto
et al. (2001) first mentioned the presence of species of Rimicaris
at hydrothermal vent field on the Rodriguez Triple Junction
on the Central Indian Ridge, Indian Ocean, and almost at the
same time Van Dover et al. (2001) reported R. aff. exoculata and
Chorocaris sp. from the same area. Watabe and Hashimoto
(2002) formally described the Rimicaris species as new, R.
kairei. The existence of a species of Chorocaris in the Indian
Ocean has not been confirmed until now. Martin and Shank
(2005) described a new species, Chorocaris paulexa Martin and
Shank 2005, from Rapa Nui Homer Vent Site on the southern
East Pacific Rise (EPR). At present, Rimicaris and Chorocaris
are represented by two (R. exoculata and R. kairei) and three
species (C. vandoverae,C. chacei, and C. paulexa), respectively.
Rimicaris exoculata and Chorocaris chacei are widespread along
the MAR in the northern hemisphere, whereas the other three
species seem to be restricted to the type and/or nearby localities,
although the density of population is sometimes very high
(Martin & Haney 2005). Rimicaris exoculata is one of the most
extensively studied vent crustaceans to date. A large number
of articles, dealing with various aspects of biology, including
morphology, ecology, behavior, and physiology has been
published (see review by Martin & Haney 2005).
This study was initiated to identify material from various
vent sites on the MAR. Two species, Rimicaris exoculata and
Chorocaris chacei, were identified, but a wide range of morpho-
logical variation observed led us to question reliability of
morphological characters used by previous authors for species
discrimination. Furthermore, a good series of material covering
various postlarval stages enabled us to investigate ontoge-
netic changes of R. exoculata and C. chacei. Consequently,
*Corresponding author. E-mail: komai@chiba-muse.or.jp
Journal of Shellfish Research, Vol. 27, No. 1, 21–41, 2008.
21
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we decided to review all described species of Rimicaris and
Chorocaris. As a result, two species of Rimicaris (R. exoculata
and R. kairei) and three species Chorocaris (C. chacei,C.
vandoverae, and C. paulexa) are confirmed to be valid. It has
been also confirmed that R. exoculata, and probably R. kairei,
undergo dramatic ontogenetic changes at early postlarval
stages. Based on examination of morphology, four sequential
stages are categorized for juveniles of R. exoculata.Rimicaris
aurantiaca and Iorania concordia both correspond to one of
these stages, and therefore the synonymy of these two taxa with
R. exoculata is fully verified. Reexamination of type material
has disclosed that juveniles of Rimicaris exoculata were mixed
in the juvenile paratypes of Chorocaris chacei, and the error is
corrected here. Most diagnostic characters for species discrim-
ination, used by previous authors, are found to be more or less
subject to intraspecific or ontogenetic variation. We have at-
tempted to find new characters useful for species discrimination.
MATERIAL AND METHODS
The type material was obtained on loan (see acknowledg-
ments). Newly obtained collections studied here came from
several diving cruises organized by French, Japanese, Ameri-
can, and German teams: HYDROSNAKE, DS Nautile/RV
L’Atalante, June 1988 (chief scientist C. Me
´vel), Mid-Atlantic
Ridge (MAR), Snake Pit (3,500 m); DIVA 2, DS Nautile/RV
L’Atalante, June 1994 (chief scientist D. Desbruye
`res), MAR,
Menez Gwen; MICROSMOKE, DSV Nautile/RV L’Atalante,
November 1995 (chief scientist D. Prieur), Snake Pit; ATOS,
ROV Victor/RV L’Atalante, July 2001 (chief scientist P.- M.
Sarradin), MAR, Lucky Strike (1,700 m) and Rainbow (2,300
m); PICO, DS Nautile/RV Nadir, July 1998 (chief scientist D.
Desbruye
`res), MAR Rainbow (2,300 m) and Lucky Strike
(1,650 m); ATOS, ROV Victor 6000/RV L’Atalante, July 2001
(chief scientist P.- M. Sarradin), MAR, Lucky Strike (1,700 m);
DiversExpedition, DS Alvin/RV Atlantis, July 2001 (chief
scientist C.L. Van Dover), MAR, Logatchev (3,010 m); ROV
Kaiko/RV Kairei, February 2002 (chief scientist J. Hashimoto),
and YK01-15, DS Shinkai 6500/RV Yokosuka, 2002 (chief
scientist J. Hashimoto), Kairei Field, Central Indian Ridge;
EXOMAR, ROV Victor 6000/RV L’Atalante, August 2005
(chief scientist A. Godfroy), MAR, TAG (3,650 m), Rainbow
(2,300 m) and Lucky Strike (1,700 m); MOMARETO, ROV
Victor 6000/RV Pourquoi Pas?, September 2006 (chief scientists
J. Sarrazin & P.-M. Sarradin), MAR, Rainbow (2,300 m) and
Lucky Strike (1,700 m); M68/1, ROV Quest 4000/RV Meteor,
May 2006 (chief scientist A. Koschinsky); SERPENTINE,
ROV Victor 6000/RV Pourquoi Pas?, March 2007 (chief sci-
entist Y. Fouquet).
The material examined is deposited in the collections in the
following institutions: Japan Marine Science and Technology
Center, Yokosuka (JAMSTEC); Muse
´um national d’Histoire
naturelle, Paris (MNHN); Natural History Museum and Insti-
tute, Chiba (CBM); Natural History Museum of Los Angeles
County(LACM);NationalMuseum of Natural History,
Smithsonian Institution (USNM); Zoologisches Institut und
Zoologisches Museum, Hamburg, Germany (ZMH).
The measurements used for different structures are defined
in Figure 1, and should be taken to the nearest 0.1 mm. An
indication of specimen size is primarily provided by the post-
orbital carapace length (PCL), measured from the level of the
posterior margin of the orbit to the midpoint of the poster-
odorsal margin. For the stage C juvenile, subadults, and adults
of Rimicaris species, in which the rostrum is greatly reduced, the
rostral carapace length (RCL), measured from the midpoint of
the rostral lobe to the midpoint of the posterodorsal margin, is
given. Maximal total length, measured from the level of the
anterior margin of the antennal scale to the posterior margin of
the telson, is also provided for each species.
Differences between species within respective genus are so
slight that a brief diagnosis is given for each species. Descriptive
terminology for the mouthparts follows that of Komai and
Segonzac (2003).
In respective synonymy, only taxonomic or systematic
references are included.
SYSTEMATICS
Family Alvinocarididae; Genus Rimicaris Williams and Rona 1986
Rimicaris Williams and Rona 1986: 447 (in part); Martin and
Hessler 1990: 8; Holthuis, 1993; Martin and Haney 2005: 467;
Iorania Vereshchaka, 1996a: 952.
Type Species
Rimicaris exoculata Williams and Rona 1986.
Figure 1. Diagrammatic Rimicaris, showing measurements used in text.
(A) Carapace in dorsal view, postorbital carapace length used for
Chorocaris spp. and stage A juvenile of Rimicaris exoculata; (B) same,
rostral carapace length including rostral lobe used for juveniles and adults
of Rimicaris spp.; (C) second segment of antennular peduncle; (D), third
pereopod, lateral view. CL, carapace length; L, length; W, width.
KOMAI AND SEGONZAC22
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Description of Adult
Body integument pitted with scattered, shallow punctua-
tions. Carapace (Fig. 2A, see 8A Later) ovate-oblong, distinctly
broader than pleon with strongly inflated branchial regions;
rostrum (Fig. 2C, see 8C see later) reduced to broadly rounded
lobe fitting closely to posterior concavity of transverse ocular
plate; dorsal surface of carapace generally rounded, obsolescent
epigastric ridge present, defined by conspicuous grooves extend-
ing from bases of antennal lobes; antennal lobes broadly rounded;
branchiostegites strongly inflated; pterygostomial expansion
covering greater part of antennal basicerite; ventral margin
closely approximating bases of pereopods (Fig. 3).
Third pleonal pleuron unarmed marginally, posterolateral
angle subrectangular; fourth and fifth pleura (Figs. 2D, 8D)
Figure 2. Rimicaris exoculata Williams & Rona, 1986. Adults. (A) Male (RCL 18.0 mm), MNHN-Na, Logatchev, Mid-Atlantic Ridge; (B-G) male
(RCL 18.0 mm), CBM-ZC 6446, Rainbow, Mid-Atlantic Ridge. (A) Carapace and cephalic appendages, dorsal view; (B) same, lateral view; (C) anterior
part of carapace and cephalic appendages, anterodorsal view; (D) fifth and sixth pleonal somites, lateral view; (E) second segment of left antennular
peduncle, anterodorsal view; (F) endopod of left first pleopod, ventral view; (G) appendices interna and masculina of left second pleopod, mesial view.
Scale bars: 5 mm for A, B; 2 mm for C, D; 1 mm for E–G.
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each with acute or subacute posteroventral angle, without other
marginal teeth or denticles. Telson slightly narrowed posteriorly;
posterior margin broadly convex, with 2 or 3 pairs of small
spines at lateral angles and row of numerous moderately long
plumose setae; six to nine dorsolateral spines arranged in
sinuous row.
Ocular region replaced by transverse ocular plate, with no
trace of eye-stalk (Fig. 2C, see 8C later). Antennae (Fig. 2C, see
8C later) forming specialized operculum-like structure covering
anterior part of cephalothorax; for detailed description, see
Martin and Hessler (1990: 6–7; antennal scale with obliquely
transverse suture distolaterally, but distolateral tooth poorly
defined. Antennular peduncles stout, somewhat depressed
dorsoventrally, contiguous, thus mesial faces flat; first segment
unarmed on distolateral and distomesial margins; dorsal sur-
face with low elevation proximolaterally, but without con-
spicuous proximolateral tubercle; stylocerite broad, closely
appressed to peduncle, reaching distolateral angle of second
segment, lateral margin notably convex; second segment nearly
as long as broad to slightly longer than broad, with moderately
large distomesial tooth. Antennal scale generally oval with
distal margin obliquely truncate, distolateral tooth absent;
dorsal surface of antennal scale with prominent middorsal
carina; basicerite with acute or subacute ventrolateral tooth,
lateral surface concave in proximal part to accommodate
expanded pterygostomial part of carapace.
Mandible and maxillule typical of family (Komai & Segonzac
2003, Komai & Segonzac 2005). Maxilla and first maxilliped
with dense covering of setae-like structure formed by bacterial
colony on ventral surfaces of scaphognathite and caridean lobe,
respectively (Fig. 6F, G see later; Segonzac 1992); posterior lobe
of scaphognathite not particularly elongate; caridean lobe of
first maxilliped extremely broad, lacking flagellum. Second
maxilliped consisting of six segments as in other alvinocaridids;
merus and ischium-basis fused segments moderately slender,
noticeably curved, with numerous heavily plumose setae on
lateral surfaces; epipod with rudimentary podobranch. Third
maxilliped consisting of four segments, concealed by the antero-
lateral part of carapace; ultimate segment stout, about 1.2 times
longer than penultimate segment, tapering distally, with some
spines on truncate distal margin; lateral surface of ultimate
segment longitudinally carinate, with row of stiff setae; cross
section trigonal; antepenultimate segment flattened dorsoven-
trally, with numerous heavily plumose setae on margins and
with prominent cluster of long setulose setae on low elevation
at proximomesial part; coxa heavily setose, with large, bilobed
epipod; no strap-like process on epipod.
First and second pereopods also practically concealed by
anterolateral part of carapace. First pereopod relatively slender,
not showing marked polymorphism as seen in other alvinocar-
idid taxa; chela typical of family, with short palm and long
fingers forming spoon-like structure; carpus with obliquely
truncate distal margin to accommodate proximal part of palm,
mesial face devoid of grooming apparatus (Fig. 6H). Second
pereopod moderately slender; chela slightly longer than carpus;
merus and ischium unarmed. Third to fifth pereopods moder-
ately stout, notably decreasing in length from third to fifth;
dactyli subconical, 0.4–0.5 length of propodi, each terminating
in strong, curved corneous unguis, flexor surfaces with nu-
merous slender corneous spinules arranged in three or four
rows (Fig. 6I); propodi each with mat of dense minute to
small corneous spinules on flexor surface (density becoming
lesser extent toward posterior pereopods) (Fig. 6I); carpi about
0.90 length of propodus in third pereopod, 0.5–0.6 in fourth
and fifth pereopods; meri and ischia setose but unarmed. No
strap-like epipods on pereopods. Gill formula typical of family
(Table 1).
Endopod of first pleopod sexually dimorphic; in male (Figs.
2F, 8F), endopod terminating in two unequal lobes, mesial lobe
longer than lateral, bearing five to seven spiniform setae; in
female, endopod simple. Second pleopod with slender, short
appendix interna, lacking cincinnuli; appendix masculina (Figs.
2G, 8G) slightly shorter than appendix interna, tapering to
subtruncate apex, with 7 to 10 spiniform setae distally. Third
pleopod lacking appendix interna. Fourth and fifth pleopods
each with well-developed, functional appendix interna, bearing
cincinnuli.
Uropod with broad rami; exopod with two small spines at
posterolateral angle and with distinct transverse suture; pos-
terolateral projection of protopod terminally blunt.
Geographical Range
Known only from hydrothermal vents along Mid-Atlantic
Ridge and Rodriguez Triple Junction on the Central Indian
Ridge, Indian Ocean.
Figure 3. Rimicaris exoculata Williams & Rona, 1986. Adult male
(RCL 19.0 mm), CBM-ZC 6446.
TABLE 1.
Branchial formula of the genus Rimicaris and Chorocaris.
r: rudimentary; *: flagellum absent.
1 2345678
Thoracic Somite
Appendages
Maxillipeds Pereopods
1 2312345
Pleurobranchs – – – +++++
Arthrobranchs – ––1111–
Podobranchs – r ––––––
Epipods +++–––––
Exopods +*–––––––
Setobranchs – –––––––
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Remarks
Two morphologically very similar species are known in
Rimicaris. Autapomorphies of the genus include: the strongly
modified ocular plate and anterior part of the carapace, the
strongly inflated anterolateral part of the carapace, the oper-
culiform antennae, and the presence of a mat of dense spinules
on the flexor surfaces of the propodi of the third to fifth pereo-
pods. Other unique characters among alvinocaridids include the
secondary lack of the proximolateral tubercle of the first seg-
ment of the antennular peduncle, the unarmed distomesial angle
of the first segment of the antennular peduncle, the stylocerite
closely approximated to the antennular peduncle, the complete
lack of the grooming apparatus on the carpus of the first pereo-
pod and the possession of the functional appendix interna on
the fourth pleopod.
Preliminary comparison of a partial sequence of mtCOI gene
by Van Dover et al. (2001) suggested that the genetic diversity
between the two species was low. Nevertheless, our study has
confirmed that the two taxa can be distinguished morpholog-
ically, as discussed later.
The loss of the grooming apparatus of the first pereopods
during the juvenile stages is highly remarkable. The functional
change of this appendage is probably related to the diet change
from food items from the surface of the habitat substrates to
bacterial colonies developed on the scaphognathite of the
maxilla and the caridean lobe of the first maxilliped. Van Dover
et al. (1988) reported that the first pereopod has a function of
scraping and grazing of filamentous bacteria covering the
scaphognathite of the maxilla and the caridean lobe of the first
maxilliped in adults of Rimicaris exoculata. Segonzac et al.
(1993) observed a notable reduction of the gut size in R.
exoculata compared with other alvinocaridid species and sus-
pected that the reduction of the gut is related to the peculiar diet
of the species, exclusively depending on bacterial colony. In
fact, filamentous bacteria are found in the gut contents (Zbinden
& Cambon-Bonavita 2003, Durand et al. in prep.). In situ
observations of adult shrimps, recorded at the Elan site of the
Snake Pit during the DiversExpedition cruise, shows that the
first and second pereopods are always inserted in the space
formed by the inflated anterolateral part of the carapace.
Similar condition is also seen in preserved specimens (Fig. 3).
Martin and Hessler (1990) described the third maxilliped of
Rimicaris exoculata as four long segments and one or two fused,
shorter, basal segments, but this is not correct. The structure
of the third maxilliped of Rimicaris is fundamentally similar to
that of other alvinocaridid species (Komai & Segonzac 2003,
Komai & Segonzac 2004, Komai & Segonzac 2005). It consists
of three long segments and coxa. The antepenultimate segment
consists of fusion of three segments, (i.e., merus, ischium and
basis). Watabe and Hashimoto (2002) gave only a diagram-
matic figure of the third maxilliped of R. kairei; there was no
mention of the segmentation of this appendage.
Rimicaris exoculata Williams and Rona 1986
Rimicaris exoculata Williams and Rona 1986: 448, Figures 4, 5,
6, 7; Williams 1987: 105; Martin and Hessler 1990: 6, Figures
3h, 4; Vereshchaka 1996b: 576–578; Segonzac 1997: 195;
Shank et al., 1998: 89 (Table 1); 1999: 247, Figure 2; Martin
and Shank 2005: 184; Martin and Harney 2005: 469; Komai
and Segonzac 2006: 428, Figures 1, 2; Komai et al., 2007.
Rimicaris chacei Williams and Rona 1986: 455 (part). See
‘‘Remarks.’’
Chorocaris n. sp.—Van Dover, 1995: 259.
Iorania concordia Vereshchaka 1996a: 954, Figures 1–5; 1996b:
577; Shank et al. 1998: 89 (Table 1).
Rimicaris aurantiaca Martin, Signorovitch and Patel 1997: 400,
Figures 1–5; Shank et al. 1998: 98 (Table 1).
Type Material Examined
Paratypes of Rimicaris chacei.TAG. NOAA VENTS Pro-
gram: 26°08.3#N, 44°49.6#W, 3620–3650 m, August 3, 1985, five
juveniles at stage B (PCL 8.4–9.2 mm), USNM 228454; one
juvenile at stage B (PCL 9.0 mm), MNHN-Na 10,535.
Paratype of Iorania concordia.TAG. BRAVEX-94: stn 3415,
26°09#N, 44°50#W, 3,650 m, September 23, 1994, one juvenile
at stage B (PCL 8.6 mm), MNHN-Na.
Other Material Examined
Rainbow
PICO (DSV Nautile): dive 1264, 36°13.81#N, 33°54.07#E,
2,285 m, 30 June 1998, slurp gun 4, one male (RCL 18.9 mm),
three females (RCL 16.2 mm–20.4 mm), MNHN-Na 16579;
same data, two males (RCL 18.0, 19.0 mm), one female (CL
19.9 mm), CBM-ZC 6446. EXOMAR (ROV Victor 6000): dive
255-06, 36°13.76#N, 33°54.17#W, 2,293 m, August 5, 2005,
slurp gun 8, nine females (RCL 14.0 mm–19.9 mm), MNHN-
Na 16580; same data, seven males (CL 14.6 mm–19.5 mm),
MNHN-Na 16581; dive 256-07, 36°13.76#N, 33°54.17#W, 2,293
m, August 6, 2005, slurp gun 3, one male (RCL 21.0 mm), seven
females (RCL 11.0–19.7 mm), MNHN-Na 16582; dive 257-08,
36°13.76#N, 33°54.16#W, 2,293 m, August 7, 2005, slurp gun
1-2-4, one male (RCL 12.0 mm), 14 subadults or females (RCL
9.2–19.6 mm), MNHN-Na 16583; dive 258-09, 36°13.76#N,
33°54.16#W, 2,293 m, August 8, 2005, slurp gun 3, one juvenile
at stage B (RCL 8.6 mm), 18 subadults or females (RCL 9.0–
13.5 mm), four males (RCL 10.5–12.3 mm), MNHN-Na 16,584.
MOMARETO (ROV Victor): dive 291-08, 36°13.75#N, 33°54.17#W,
2,297 m, August 19, 2006, slurp gun 1, three females (RCL 18.0–
18.3 mm), one male (RCL 19.6 mm), CBM-ZC 9388.
TAG
EXOMAR (ROV Victor 6000): dive 260-11, 26°08.22#N,
44°49.56#W, 3,632 m, August 13, 2005, slurp gun 3, one juvenile
at stage A (PCL 5.2 mm), MNHN-Na; same data, 26 juveniles
at stage B (PCL 7.4–9.6 mm), MNHN-Na 16586; same data, 11
juveniles at stage C (RCL 7.1–8.6 mm), MNHN-Na 16587; 18
subadults or females (RCL 8.0–16.3 mm), one male (RCL 15.7
mm), MNHN-Na 16585; same dive, slurp gun 4, five males
(RCL 12.5–15.2 mm), 13 subadults or females (RCL 9.2–14.9
mm), three juveniles at stage B (PCL 8.0–9.4 mm), CBM-ZC
9389; dive 262-13, slurp gun 1, four males (RCL 13.6–15.0 mm),
six females (RCL 14.0–15.3 mm), CBM-ZC 9390.
Snake Pit
MICROSMOKE (DSV Nautile): dive 01, site Elan,
23°22.20#N, 44°57.08#W, 3,500 m, November 14, 1995, one
REVIEW OF RIMICARIS AND CHOROCARIS 25
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juvenile at stage B (PCL 7.3 mm), one juvenile at stage C
(RCL 8.3 mm), four juveniles at stage D (RCL 8.6–8.8 mm),
MNHN-Na; dive 02, site Ruches, 23°22.13#N, 44°57.13#W,
3,480 m, November 15, 1995, four males (RCL 18.1–19.1 mm),
three females (RCL 10.6–18.5 mm), seven juveniles at stage
B (PCL 7.0–9.0 mm), 12 juveniles at stage C (RCL 6.6–8.2 mm),
nine subadults (RCL 7.5–9.0 mm), MNHN-Na. Divers-
Expedition (DSV Alvin): dive 3672, 23°22.10#N, 44°56.91#W,
3,492 m, July 14, 2001, 77 juveniles at stage A (PCL 4.8–5.3
mm), one juvenile at stage B (PCL 8.4 mm), one juvenile at stage
C (RCL 7.3 mm), two subadults (RCL 7.7, 8.9 mm), MNHN-
Na 16588; same data, one male (RCL 16.3 mm), 13 subadults or
adult females (RCL 8.0–13.0 mm), MNHN-Na.
Logatchev
DiversExpedition (DSV Alvin): dive 3668, 14°45.32#N,
44°58.79#W, 3028 m, 8 July 2001, 61 juveniles at stage B
Figure 4. Rimicaris exoculata Williams & Rona, 1986. Juvenile at stage A (PCL 4.2 mm), MNHN-Na 16588, Snake Pit, Mid-Atlantic Ridge. (A)
Carapace, dorsal view; (B) carapace and cephalic appendages, lateral view; (C) anterior part of carapace and cephalic appendages, dorsal view; (D)
posterior part of telson, dorsal view; (E) left maxilla, ventral view; (F) left first maxilliped, ventral view; (G) left third maxilliped, lateral view; (H) carpus
of left first pereopod, mesial view; (I) left second pereopod, lateral view; (J) left third pereopod, lateral view. Scale bars: 1 mm for A-C; 0.5 mm for D-J.
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(PCL 7.4–9.1 mm), 59 juveniles at stage C (RCL 7.4–9.1 mm),
67 subadult or adult females (RCL 7.8–13.8 mm), 31 males
(RCL 10.1–22.0 mm) MNHN-Na 16589. SERPENTINE
(ROV Victor 6000): dive 315–06, Irina 2, 14°45.18#N,
44°58.74#W, 3,021 m, March 20, 2007, slurp gun 2, five juve-
niles at stage B (PCL 7.5–7.9 mm), six juveniles at stage C
(RCL 7.9–9.5 mm), 16 subadults or adult females (RCL 8.5–
17.4 mm), three males (RCL 13.4–15.5 mm), MNHN-Na
16700; same data, five ovigerous females (RCL 15.2–18.4
mm), MNHN-Na 16701; same site, slurp gun 5, one
juvenile at stage A (PCL 4.9 mm), MNHN-Na 16702; dive
316-07, same site, 14°45.17#N, 44°58.74#W, 3,022 m, slurp
gun 4, 13 juveniles at stage A (PCL 4.4–5.0 mm), two juveniles
at stage B (RCL 7.9, 8.2 mm), MNHN-Na 16703.
Figure 5. Rimicaris exoculata Williams & Rona, 1986. Juvenile at stage B (PCL 9.0 mm), MNHN-Na 16589, Logatchev, Mid-Atlantic Ridge. (A)
Carapace, dorsal view; (B) anterior part of carapace and cephalic appendages, lateral view; (C) same, dorsal view; (D) posterior margin of telson, dorsal
view; (E) left first maxilliped, ventral view; (F) left third maxilliped, lateral view; (G) carpus of left first pereopod, mesial view; (H) left second pereopod,
lateral view; (I) left third pereopod, lateral view; (J) dactylus of left third pereopod, flexor view. Scale bars: 2 mm for A; 1 mm for B, C, F, H, I; 0.5 mm
for D, E, G, J.
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Ashadze
SERPENTINE (ROV Victor 6000): dive 313-4, site Ashadze
1, marker SE1, 12°58.34#N, 44°51.77#W, 4,088 m, March 15,
2007, slurp gun 3, one juvenile at stage C (RCL 8.6 mm),
MNHN-Na 16,699.
Mephisto
RV Meteor,M68/1(ROVQuest 4000): stn 7, ROV-2,
04°47.834#S, 12°22.593#W, 3045 m, wall of hot smoker, May
11, 2006, one female (RCL 18.4 mm), one ovigerous female
(RCL 19.4 mm), ZMH K-41458.
No collection data
Sixty females including subadults (RCL 8.3–20.4 mm),
MNHN-Na 11872.
Diagnosis of Adult
Carapace and pleon with scattered tufts of short setae (Fig.
2A to D); anterolateral part stronglyinflated but degree
lesser extent to that of R. kairei. Antennular peduncle relatively
stout; second segment (Fig. 2E) 1.21–1.59 times longer than wide
(showing tendency toward increase of value with increase of
body size).
Figure 6. Rimicaris exoculata Williams & Rona, 1986. Juvenile at stage C (RCL 8.3 mm), MNHN-Na 16589, Logatchev, Mid-Atlantic Ridge.
(A) Carapace, dorsal view; (B) anterior part of carapace and cephalic appendages, lateral view; (C) same, dorsal view; (D) fused eye-stalks, dorsal view;
(E) posterior part of telson, dorsal view; (F) left maxilla, ventral view; (G) left first maxilliped, ventral view; (H) carpus of left first pereopod, mesial view;
(I) dactylus and propodus of left third pereopod, lateral view. Scale bars: 2 mm for A; 1 mm for B-D, F, G; 0.5 mm for E, H, I.
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Description
See Williams and Rona (1986) for adults; see Vereshchaka
(1996a) and Martin et al. (1997) for juvenile of the stage B
(see below).
Ontogenetic Change in Postlarval Stages
Examination of the abundant material of postlarval stages,
covering a wide range of size, has shown that Rimicaris
exoculata exhibits dramatic morphological change at size of
7.0–9.0 mm in carapace length as seen by Shank et al. (1998).
The smallest male specimen determined by the pleopod mor-
phology is 10.1 mm in the orbital carapace length. For con-
venience, four stages are categorized for those juveniles based
on morphological characters. Features of each stage are
summarized as follows.
Stage A (Fig. 3). CL 4.8–5.3 mm. Rostrum (Fig. 4A, C)
bluntly triangular in dorsal view, reaching nearly to midlength
of first segment of antennular peduncle; dorsal surface convex,
unarmed; lateral carina extending to orbital margin; ventral
surface convex. Carapace (Fig. 4A, B) without epigastric ridge;
antennal lobe obsolete; pterygostomial angle only slightly pro-
duced, rounded or slightly angular; postantennal groove shal-
low; branchiostegite not inflated; surface devoid of tufts of
setae. Telson with five or six dorsolateral spines arranged in
straight row; posterior margin (Fig. 4D) fringed with row of
slender spines. Eye-stalks (Fig. 4B, C) fused mesially, with small
papilla-like tubercle on anterior surface medially; cornea
reduced, not faceted, but still recognizable; dorsal eyes extend-
ing posterior to about anterior 0.20 of carapace. Antennular
peduncles (Fig. 4B, C) stout, but not closely approximated; first
segment with small distolateral tooth partially obscured by
setae on distal margin of segment; stylocerite reaching mid-
length of second segment, clearly separated by first segment by
moderately narrow hiatus, lateral margin slightly convex.
Antennal scale (Fig. 4C) not tightly fitting against antennular
peduncle, with small, subacute distolateral tooth far exceeded
by broadly rounded distal lamella; basicerite (Fig. 4B) with
acute ventrodistal lateral tooth, not covered by pterygostomial
projection of carapace. Maxilla (Fig. 4E) similar to that of adult
in general shape, but surfaces naked. First maxilliped (Fig. 4F)
with caridean lobe moderately expanded, surfaces with few,
weakly plumose setae; exopodal flagellum long. Second maxil-
liped moderately stout, not heavily setose; merus and ischium
straight. Third maxilliped (Fig. 4G) with ultimate and penulti-
mate segment combined longer than antepenultimate segment;
antepenultimate with slender spine at ventrolateral distal angle.
First pereopod with carpus (Fig. 4H) nearly as long as high;
mesial face with grooming apparatus ventrally, consisting of
small spine and patch of stiff setae. Second pereopod (Fig. 4I)
with small spine on lateral surface ventrally; ischium unarmed.
Third to fifth pereopods (Fig. 4J) diminishing slightly in length
toward posterior; dactyli each with two rows of accessory
spinules on flexor surface; propodi each with two rows of sparse
spinules on flexor surface; meri each with three or four spines on
lateral surface ventrally; ischia each with one or two spines on
lateral surface ventrally. Appendices internae on second and
third pereopods rudimentary buds, those of fourth and fifth
pleopods fully developed, with terminal cluster of cincinnuli.
Stage B (Fig. 5). CL 7.0–9.5 mm. Rostrum (Fig. 5A, C)
rounded, reaching tip of antennal lobe; ventral surface slightly
convex or flat. Carapace (Fig. 5A to C) with scattered tufts of
very short setae or single setae on surface; noticeably produced
pterygostomial lobe partially covering antennal basicerite, but
otherwise similar to that of stage A. Telson with seven to nine
dorsolateral spines arranged in faintly sinuous row; posterior
margin (Fig. 5D) fringed with slender spinules. Eye-stalks
(Fig. 5C) generally similar to those of stage A, but papilla-like
tubercles on anterior surface of corneal region reduced. Anten-
nular peduncles (Fig. 5B, C) becoming stouter and more closely
approximated; first segment with distolateral tooth greatly
reduced to tiny projection and with distinct distomesial tooth;
stylocerite reaching distal margin of second segment, still nar-
rowly separated from first segment, lateral margin noticeably
convex. Antennal scale (Fig. 5C) becoming broader, but still not
tightly fitting against antennular peduncle, with trace of disto-
lateral tooth; basicerite (Fig. 5B) partially covered by pterygos-
tomial projection of carapace. Maxilla similar to that of stage
A. First maxilliped (Fig. 5E) with broad caridean lobe, but
facial plumose setae few, restricted to adjacent to margins;
exopodal flagellum still developed, reaching or distinctly over-
reaching anterior margin of caridean lobe. Second maxilliped
becoming more slender and more setose. Third maxilliped (Fig.
5F) with distal two segments combined distinctly shorter than
antepenultimate segment; slender spine at ventrodistal lateral
angle of antepenultimate segment missing. First pereopod with
carpus (Fig. 5G) being longer than high, with small tuft of short
setae on ventral margin, representing rudiment of grooming
apparatus. Second pereopod (Fig. 5H) unarmed on merus.
Third pereopod (Fig. 5I) with more than two rows of accessory
spinules on flexor surface of dactylus (Fig. 5J); propodus
becoming shorter proportionally, with mat of dense spinules
extending to midlength of flexor surface, followed by two rows
of spinules in proximal half; merus unarmed or one or two
spines; ischium with one or two spines. Fourth and fifth pereo-
pods with less spinose flexor surfaces of propodi; each merus
unarmed or armed with one to four spines on lateral surface;
ischium unarmed or armed with one or two spines on lateral
surface. Appendices internae on second and third pereopods
short and slender, lacking cincinnuli; those on fourth and fifth
pereopods stout, functional.
Figure 7. Rimicaris exoculata Williams & Rona, 1986. Subadult (RCL
8.9 mm), MNHN-Na 16588, Snake Pit, Mid-Atlantic Ridge. (A)
Carapace and ocular plate, dorsal view; (B) anterior part of carapace and
cephalic appendages, anterodorsal view. Scale bars: 2 mm for A; 1 mm
for B.
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Stage C (Fig. 6). CL 6.6–8.2 mm. Rostrum (Fig. 6C, D)
reduced to broadly rounded rostral lobe. Carapace (Fig. 6A
to C) with pterygostomial angle strongly produced anteriorly,
rounded; branchiostegite weakly inflated. Telson with seven to
nine dorsolateral spines arranged in sinuous row; posterior
margin (Fig. 6E) fringed with row of plumose setae. Eye-stalks
(Fig. 6D) broadly fused mesially but with trace of median notch
on anterior surface; separation of cornea and eye-stalk unclear;
no papilla-like tubercle on eye-stalk. Antennular peduncles
(Fig. 6B, C) stout, closely approximated as in adult; first
segment unarmed on distolateral and distomesial angles; stylo-
cerite closely appressed to antennular peduncle, lateral margin
strongly convex. Antennal scale (Fig. 6B, C) tightly fitting
against antennular peduncle, without distolateral tooth but
with short transverse groove distolaterally; basicerite partially
covered by pterygostomial projection of carapace. Maxilla
(Fig. 6F) with numerous plumose setae-like structure formed
by bacteria on surfaces of scaphognathite. First maxilliped (Fig.
6E) with or without trace of flagellum of exopod; caridean lobe
broad, with numerous heavily plumose setae on surfaces. Sec-
ond maxilliped with merus and ischium slightly curved. Carpus
of first pereopod (Fig. 6H) without trace of grooming appara-
tus. Other appendages as in previous stage.
Stage D, or subadults (Fig. 7). CL 7.5 mm or more. Gener-
ally similar to adults (see ‘‘Diagnosis’’ of the genus), but infla-
tion of carapace still weaker than adults (Fig. 7A). Ocular plate
completely formed, fused with anterodorsal part of carapace
(Fig. 7B).
Size
Ovigerous females RCL 15.2–19.4 mm; males RCL 10.6–
22.0 mm. The largest specimen is the male RCL 22.0 mm, TL
about 70 mm.
Distribution
Mid-Atlantic Ridge, hydrothermal vent fields at Rainbow,
Lucky Strike, TAG, Snake Pit, Broken Spur, Logatchev,
Ashadze, and Mephisto sites, 1,700–4,088 m. The specimen
from Ashadze 1 site extends the bathymetric range of the species
to 4,088 m.
Remarks
Adult specimens from TAG, Rainbow, Snake Pit,
Logatchev, Ashadze and Mephisto vent sites were available
for study. The specimens are generally similar, and there is little
doubt that they represent a single species. In fact, based on
allozyme data, Creasey et al. (1996) showed that the genetic
variation in the populations from TAG and Broken Spur was
low. Vereshchaka (1997b) reported statistically significant
divergence between two populations within the TAG vent field,
but we could not find any morphological differences of species
level significance.
As shown earlier, the juveniles can be categorized in four
sequential stages. It is remarkable that there is no significant
increase of size during molts from the stage B to stage D. It
can be assumed that the shrimp spends much energy for great
morphological change rather than increase of body size. The
most notable change is seen in the structure of the anterior part
of the carapace, eye-stalks and antennae. Also, the reduction of
the exopod on the first maxilliped and the loss of the grooming
apparatus on the carpus of the first pereopod are also remark-
able. The loss of the spination on the second to fifth pereopods
is here documented for the first time. Most of the structures are
completed at the stage D (subadult).
Shank et al. (1998, 1999) showed that Iorania concordia and
Rimicaris aurantiaca were described from juvenile stage of R.
exoculata based on studies of allozyme and mtDNA. Our study
confirms the conclusion of Shank et al. (1998, 1999). Reexami-
nation of the type material of I. concordia and R. aurantiaca
(one paratype was available for I. concordia; the holotype and
paratypes were available for R. aurantiaca) has shown that all
specimens of the two nominal taxa correspond to the stage B
juvenile of R. exoculata. The paratype of I. concordia (MNHN-
Na) seems to be just before molting, with the rostral margin of
the next molt is visible throughout the integument. The visible
rostral margin of the next molt is less produced as illustrated
and is similar to the configuration of the rostral margin in the
stage C. This provides further evidence that the stages catego-
rized here can be aligned in an ontogenetic sequence.
Juveniles of the stages A and B of Rimicaris exoculata are
similar to juveniles of Chorocaris chacei of similar sizes. The
two species occur sympatrically, and it is easy to confuse them
without careful observation. In fact, some paratypes of C.
chacei are actually R. exoculata. Throughout the juvenile stages,
Rimicaris exoculata is distinguishable from C. chacei by the less
developed distolateral tooth of the first segment of the anten-
nular peduncle. In the stage A juvenile, the distolateral tooth is
small, and partially obscured by setae on the dorsodistal margin
of the first peduncular segment; in the stage B juvenile, the tooth
is missing. In C. chacei, the distolateral tooth is always
conspicuous, reaching to the midlength of the second pedun-
cular segment (Fig. 11A, see later). Furthermore, the stage A
juveniles of R. exoculata is distinguishable from juveniles of
C. chacei by the more strongly produced rostrum (cf. Fig. 4A
and Fig. 11A), the presence of spiniform setae on the posterior
margin of the telson (Fig. 4D), and the meri of the second and
third pereopod being armed with lateral spine(s) (Fig. 4J). In
juveniles of C. chacei, the posterior margin of the telson bears
plumose setae mesial to the two posterolateral pairs of spines
(Fig. 11C), instead of spiniform setae; and the meri of the
second and third pereopod are unarmed (Fig. 10E). The stage B
juveniles of R. exoculata differ from juveniles of C. chacei in the
relatively broader rostrum and the lack of a grooming appara-
tus on the carpus of the first pereopod. Chorocaris chacei has a
well-developed grooming apparatus on the carpus of the first
pereopod throughout the postlarval stage to adult.
Rimicaris kairei Watabe and Hashimoto 2002 (Fig. 8)
Rimicaris aff. exoculata—Van Dover et al. 2001: 820, Figure
2A, B, G.
Rimicaris kairei Watabe and Hashimoto 2002: 1168, Figures 1
to 4; Martin and Shank 2005: 184; Martin and Haney 2005:
469; Hashimoto 2006: 429, Figures 1, 2.
Material Examined
DSV Shinkai 6500: dive 659, Kairei Field, Rodriguez Triple
Junction, Central Indian Ridge, 25°19.22#S, 70°02.39#E, 2,415–
2,460 m, February 15, 2002, 3 males (RCL 12.1–20.8 mm),
7 nonovigerous females (RCL 12.5–22.9 mm), JAMSTEC
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047496. ROV Kaiko:dive168,samefield,25°19.16#S,
70°02.40#E, 2,452 m, August 26, 2000; 6 females (RCL 12.6–
15.0 mm), JAMSTEC 032683–032851.
Diagnosis of Adult
Carapace and pleon completely naked on surface (Fig. 7A to
D); anterior part of branchial region more strongly inflated than
in R. exoculata (Fig. 7A). Antennular peduncle relatively slen-
der; second segment (Fig. 7E) 1.57–1.86 times longer than wide.
Description
See Watabe and Hashimoto (2002).
Size
Males RCL 12.1–20.8 mm. Largest specimen, a female, RCL
22.9 mm, TL ca. 73 mm.
Figure 8. Rimicaris kairei Watabe & Hashimoto, 2002. A to E, female (RCL 17.4 mm), JAMSTEC 047496, Kairei Field, Central Indian Ridge; F, G,
male (RCL 20.5 mm), same lot. (A) Carapace and cephalic appendages, dorsal view; (B) same, lateral view; (C) anterior part of carapace and cephalic
appendages, anterodorsal view; (D) fifth and sixth pleonal somites, lateral view; (E) second segment of left antennular peduncle, anterodorsal view; (F)
endopod of left first pleopod, ventral view; (G) appendices interna and masculina of left second pleopod, mesial view. Scale bars: 5 mm for A, B; 2 mm for
C to E; 1 mm for F, G.
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Distribution
Known only from Kairei and Edmonds vent fields at the
Rodriquez Triple Junction on the Central Indian Ridge, Indian
Ocean, 2,415–3,320 m.
Remarks
Watabe and Hashimoto (2002) cited three morphological
characters in differentiating R. kairei and R. exoculata; the
presence or absence of tufts of short setae on the carapace
and pleon (tufts of setae are absent in R. kairei, present in R.
exoculata), the relative length of the antennal flagellum (longer
in R. kairei than in R. exoculata), and the shape of the second to
fifth pereopods (the pereopods are more slender in R. kairei
than in R. exoculata). Our study has shown that the latter two
characters are not reliable, because the proportional values
greatly overlap between R. kairei and R. exoculata, as summa-
rized in Table 2. Even statistically, there are no significant
differences between the mean values of the two species (the
length of the antennal flagellum: t¼1.5616, degree of freedom
18, P>0.05; the proportion of the merus of the third pereopod:
t¼0.1098, degree of freedom 34, P>0.05). Only two specimens
of R. exoculata were available to Watabe and Hashimoto
(2002), and therefore, it is obvious that their evaluation of
intraspecific variation was inadequate. Nevertheless, the first
character is still reliable in distinguishing the two species
throughout subadult to adult stages. Additionally, the anten-
nular peduncle is less stout in R. kairei than in R. exoculata. The
proportion of the second segment is used as an indicator.
The second segment is 1.57 to 1.86 times longer than wide in R.
kairei, 1.21 to 1.59 in R. exoculata. The branchial region of the
carapace seems to be more strongly inflated in R. kairei than in
R. exoculata (Fig. 2A and Fig. 8A).
During this study, no juvenile specimens have been available
to us, but we suspect that R. kairei also has dramatic ontoge-
netic change in early postlarval stage as in R. exoculata.
Genus Chorocaris Martin and Hessler 1990
Rimicaris Williams and Rona 1986: 447 (in part).
Chorocaris Martin and Hessler 1990: 2 (in part); Holthuis 1993:
72; Martin and Haney 2005: 463.
Description
Body integument pitted with scattered, very shallow punc-
tations or nearly smooth. Rostrum broadly rounded or bluntly
triangular, reaching or slightly overreaching anterior margins
of broadly fused eye-stalks; dorsal surface rounded, unarmed;
ventral surface convex or flat. Carapace nearly as broad as
pleon; dorsal surface rounded; antennal tooth weak, blunt or
showing as broadly rounded lobe; anterolateral part only
slightly inflated; pterygostomial expansion at most partially
covering antennal basicerite; ventral margin not closely approx-
imating bases of pereopods.
Third pleonal pleuron unarmed marginally, posterolateral
angle rounded; fourth and fifth pleura each with blunt or
subacute posteroventral angle, without marginal teeth or
denticles. Telson broad, slightly narrowed posteriorly; posterior
margin broadly convex, with two or three pairs of small spines
at lateral angles and row of numerous moderately long plumose
setae; six to nine dorsolateral spines arranged in sinuous row.
Eye-stalks broadly fused mesially; no conspicuous tubercles
on anterior surface. Antennae normal in structure. Antennular
peduncles stout, somewhat depressed dorsoventrally, not
closely approximated, thus mesial face rounded; first segment
with strong distolateral and small distomesial teeth; dorsal
surface convex, groove separating stylocerite deep; stylocerite
moderately slender, clearly separated from first segment, reach-
ing or overreaching midlength of second segment, its lateral
margin slightly convex; proximolateral tubercle prominent;
second segment nearly as long as broad to slightly longer than
broad, with small distomesial tooth. Antennal scale generally
oval with distal margin broadly rounded, blunt distolateral
tooth present; short transverse suture extending mesially from
base of distolateral tooth; dorsal surface with prominent mid-
dorsal carina; basicerite with subacute ventrolateral tooth.
Mandible and maxillule typical of family. Maxilla and first
maxilliped with numerous plumose seta-like structures on
ventral surfaces in C. chacei, without such seta-like structures
in C. vandoverae and C. paulexa; posterior lobe of scaphogna-
thite somewhat elongate; caridean lobe of first maxilliped
broad, lacking flagellum. Second maxilliped consisting of six
segments as in other alvinocaridids; merus and ischium-basis
fused segments moderately stout, nearly straight, with numer-
ous heavily plumose setae on lateral margins; epipod large,
subsemicircular, with rudimentary podobranch. Third maxilli-
ped consisting of four segments; ultimate segment stout, 1.2–1.3
times longer than penultimate segment, tapering distally, with
some spines distally; lateral surface of ultimate segment longi-
tudinally carinate, with row of stiff setae; cross section trigonal;
antepenultimate segment flattened dorsoventrally, with numer-
ous heavily plumose setae on margins and with prominent
cluster of long setulose setae on low elevation at proximomesial
part; coxa with large, bilobed epipod; no strap-like process on
epipod.
First pereopod typical of family, polymorphic; carpus with
obliquely truncate distal margin to accommodate proximal part
of palm, mesial face with grooming apparatus consisting of
patch of stiff setae and one or two spinules (Fig. 9E). Second
pereopod moderately slender; chela slightly longer than carpus;
merus and ischium unarmed. Third to fifth pereopods moder-
ately stout, similar in structure but slightly increasing in relative
length from third to fifth; dactyli subconical, 0.3–0.4 length of
TABLE 2.
Variation in the length of the antennal flagellum and the
proportion of the merus of the third pereopod in two Rimicaris
species. Abbreviations: AFL, length of antennal flagellum; CL,
carapace length; ML, length of merus; MW, width of merus;
P3, third pereopod.
AFL/CL P3 ML/MW
Rimicaris exoculata
Male 1.59–2.44 (n¼6) 3.90–4.86 (n¼10)
Female 1.23–2.17 (n¼4) 4.39–4.69 (n¼11)
Rimicaris kairei
Male 1.64 (n¼1) 4.27–4.41 (n¼2)
Female 1.20–1.88 (n¼7) 4.14–4.67 (n¼14)
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propodi, each terminating in strong, curved corneous unguis,
flexor surface with about ten corneous, distally curved, spinules
arranged in three or four rows; propodi increasing in length
from third to fifth, each with three or four spinules on
ventrodistal margin and irregular two rows of spinules on
ventral surface in third and fourth, with double row of spinules
laterally and single row of sparse spinules mesially in fifth; carpi
0.7–0.9 length of propodi in third and fourth pereopods, 0.5–0.6
in fifth pereopod; meri and ischia unarmed. No strap-like
epipods on pereopods. Gill formula typical of family (Table 1).
Endopod of first pleopod sexually dimorphic; in male,
endopod (Figs. 9F, 10D) terminating in two greatly unequal
lobes, mesial lobe much produced, with four or five long
spiniform setae directed mesially; in female, endopod simple.
Second pleopod with slender appendix interna, lacking cincin-
nuli (Figs. 9G, 10E); appendix masculina slightly shorter than
Figure 9. Chorocaris chacei (Williams & Rona 1986). (A to D) Ovigerous female (PCL 16.5 mm), MNHN-Na 16568, Lucky Strike, Mid-Atlantic
Ridge; (E) female (PCL 21.5 mm), CBM-ZC 9391, same locality; (F, G) male (PCL 15.3 mm), CBM-ZC 9392, same locality. (A) Carapace and eye-
stalks, dorsal view; (B) carapace and cephalic appendages, lateral view; (C) anterior part of carapace and cephalic appendages, anterodorsal view; (D)
same, lateral view; (E) protopod of left uropod, dorsolateral view; (F) anterior part of carapace and ocular appendage, lateral view; (G) same, dorsal view.
Scale bars: 5 mm for A, B; 2 mm for C, D, F, G; 1 mm for E.
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appendix interna, tapering distally, with several spiniform setae.
Third and fourth pleopods each with slender appendix interna
lacking cincinnuli. Fifth pleopods with normally developed,
functional appendix interna, bearing cincinnuli.
Uropod with broad rami; exopod with two small spines at
posterolateral angle and with distinct transverse suture; pos-
terolateral projection of protopod terminally blunt.
Composition
Chorocaris chacei (Williams and Rona, 1986); C. vandoverae
Martin and Hessler 1990 (type species); and C. paulexa Martin
and Shank 2005.
Geographical Range
Mid-Atlantic Ridge (between 23°N and 37°N), Mariana
Back-Arc Basin in the northwestern Pacific and southern East
Pacific Rise.
Remarks
Presumable synapomorphies among species of Chorocaris
and Rimicaris are the following: the tendency of a rostral reduc-
tion, nonacuminate antennal tooth of the carapace, nonmargi-
nally dentate posterolateral margin of pleura of fourth and fifth
pleonal somites, the presence of a distolateral transverse suture
on the antennal scale, and the nonacuminate uropodal proto-
pod. Shank et al. (1999) suggested that Chorocaris is a para-
phyletic assemblage with C. chacei being more closely related to
Rimicaris exoculata. Consequently, we tried to identify syna-
pomorphies of C. chacei and R. exoculata. It is interesting to
note that the specimens of C. chacei in spawning molt have
suboperculiform antennae, which are distinctly directed down-
ward, like adults of Rimicaris species; the rostrum is reduced to
a broadly rounded lobe, although the degree of the reduction is
in a lesser extent than in Rimicaris. In the ovigerous specimens
of C. vandoverae and C. paulexa the antennae are normal, only
Figure 10. Chorocaris chacei (Williams & Rona, 1986). (A, B, C, E) Female (PCL 13.2 mm), MNHN-Na 16571, Lucky Strike, Mid-Atlantic Ridge;
(D) holotype, female (cl 17.9 mm), USNM 228452, TAG, MidAtlantic Ridge; (F, G) male (cl 11.5 mm), MNHN-Na, Lucky Strike, Mid-Atlantic Ridge.
(A) Carapace and cephalic appendages, dorsal view; (B) anterior part of carapace and cephalic appendages, dorsal view; (C) chela of right first pereopod,
inner view; (D) chela of left first pereopod, inner view; (E) carpus of left first pereopod, mesial view; (F) endopod of left first pleopod, ventral view;
(G) appendices interna and masculina of left second pleopod, mesial view. Scale bars: 5 mm for A; 2 mm for B; 1 mm for C, D-F; 0.5 mm for G.
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slightly directed downward; the rostrum is short but still more
distinct. Comparison with other alvinocaridid taxa clearly
suggests that the possession of suboperculiform antennae and
the reduction of the rostrum are apomorphic. Furthermore,
ovigerous females of C. chacei lack shallow longitudinal
depressions, ornamented with numerous longitudinal striae,
on either side of the midline of the carapace, which are present
in ovigerous females of C. vandoverae and C. paulexa. Species of
Rimicaris also do not possess such depressions on the carapace
in spawning females. In C. vandoverae and C. paulexa, the
scaphognathite of the maxilla and the caridean lobe of the first
maxilliped are nearly naked on the ventral surfaces, whereas in
C. chacei, they are provided with numerous plumose seta-like
structures on the surfaces, like Rimicaris species. The structure
of the appendix masculina is also similar between C. chacei and
Rimicaris species. The appendix masculina is armed with several
spiniform setae distally in C. chacei and two Rimicaris species,
but in C. vandoverae, a row of spiniform setae extends onto the
dorsal surface of the appendix masculina. Male specimens of C.
paulexa were not available for study. The observation seems to
support the proximity between C. chacei and Rimicaris species.
Nevertheless, in this study, we did not attempt to establish a new
genus for C. chacei, because we believe that highly corroborated
phylogeny is necessary for the establishment of a new higher
taxon for such a specific taxon with morphologically similar
species. Furthermore, we could not identify single, stable
character for discrimination. Most of the characters above cited
are affected by ontogeny or sex. For the time being, Chorocaris
should be considered as a possible paraphyletic taxon.
Differentiation between Chorocaris and Opaepele Williams
and Dobbs 1995 now appears rather delicate (Komai et al.,
2007). Nevertheless, Opaepele can be distinguished from Cho-
rocaris by the acuminate antennal and pterygostomial teeth of
the carapace, the denticulate posterolateral margin of the fifth
pleonal pleuron, the well differentiated, sharp distolateral tooth
of the antennal scale and the sharply pointed posterolateral
projection of the uropodal protopod. Mirocaris superficially
resembles Chorocaris, but the presence of strap-like epipods
immediately distinguishes Mirocaris from Chorocaris. In the
MidAtlantic Ridge, species of the two genera are often found
sympatrically, and it is advisable to check the presence or
absence of pereopodal epipods for accurate identification.
Unidentified specimens provisionally assigned to Chorocaris
have been reported (Martin & Haney 2005). Desbruye
`res et al.
(1994) noted the possibility of existence of Chorocaris species
in material from Lau and North Fiji Basin, but since then no
specimens referable to Chorocaris have been collected from
these localities. Van Dover et al. (2001) recorded Chorocaris sp.
from Kairei Field, Central Indian Ridge, but the occurrence of
species of Chorocaris in the vent fields on the Central Indian
Ridges has not been confirmed. Komai et al. (2006) indicated
that Chorocaris sp. of Van Dover et al. (2001) might be identical
with Mirocaris indica Komai, Martin, Zala, Tsuchida and
Hashimoto 2006, a species described from Kairei and Edmond
vent fields, because of its superficial resemblance to species of
Chorocaris. A few specimens of a shrimp species that appear to
belong to Chorocaris have been found on seamounts of the
Kermadec Ridge off New Zealand (Webber, 2004). This record
also needs to be verified.
Species of Chorocaris are distinguished by subtle morpho-
logical differences, some of which are growth-related. There-
fore, in the following key, different stages or sexes of a same
species are treated separately.
Key to Species of Chorocaris (Adult)
1. a. Carapace with shallow longitudinal depression on either
side of dorsal midline ..................................................... 2
b. Carapace without shallow longitudinal depression on
either side of dorsal midline .......................................... 3
2. a. Pterygostomial projection terminally blunt; rostrum rela-
tively large; distolateral tooth of antennal scale blunt,
closely approximated to lamella, thus apparently incon-
spicuous ...................... C. vandoverae (spawning females)
b. Pterygostomial projection subacutely pointed; rostrum
relatively small; distolateral tooth of antennal scale sub-
acute, clearly separated from lamella by V-shaped notch..
.......................................... C. paulexa (spawning females)
3. a. Antennal tooth of carapace broadly rounded...................
............................................ C. chacei (spawning females)
b. Antennal tooth of carapace blunt, but clearly delin-
eated............................................................................... 4
4. a. Pterygostomial expansion subacutely pointed; distolateral
tooth of antennal scale distinctly delineated.....................
.................................... C. paulexa (nonspawning females)
b. Pterygostomial expansion rounded................................ 5
5. a. Rostrum with nearly straight lateral margins; distolateral
tooth of antennal scale small, but distinctly separated from
lamella by V-shaped notch; plumose seta-like structures
present on ventral surfaces of scaphognathite of maxilla
and caridean lobe of first maxilliped; appendix masculina
only with terminal or subterminal spines ........................
........................ C. chacei (males or nonspawning females)
b. Rostrum with weakly convex lateral margins; distolateral
tooth of antennal scale blunt, closely approximated to
lamella; no plumose seta-like structures present on ventral
surfaces of scaphognathite of maxilla and caridean lobe of
first maxilliped; appendix masculina with terminal spines
and rows of spines extending onto dorsal surface ..........
................ C. vandoverae (males or nonspawning females)
Chorocaris chacei (Williams & Rona 1986 Figs. 9–11)
Rimicaris chacei Williams and Rona 1986: 455 (in part), Figures
5–7; Williams 1987: 105.
Chorocaris chacei – Martin and Hessler 1990: 2, 8, Figure 3f, g;
Martin and Hessler 1990: 6, Figures 3h, 4; Segonzac et al.
1993: 540 and addendum (part); Vereshchaka 1996b: 577;
Shank, in Desbruye
`res and Segonzac 1997: 195; Shank et al.
1998: 89 (Table 1); 1999: 246 (Table 1), 247 (Table 2), 249,
Figure 2; Martin and Shank 2005: 184; Martin and Haney
2005: 464; Komai and Segonzac 2006: 421, Figures 1–5.
Type Material
Holotype. TAG. NOAA VENTS Program (RV Researcher):
26°08.3#N, 44°49.6#W, 3,620–3,650 m, August 3, 1985, dredge,
female (PCL 18.3 mm), USNM 228452.
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Paratypes: Same data as holotype, one female (PCL 16.4
mm), USNM 228453.
Other Material
Lucky strike
DIVA 2 (DS Nautile): dive 09/920, June 11, 1994, slurp gun
10, one female (PCL 15.5 mm), MNHN-Na; dive 24/935, 1,600–
1,700 m, June 30, 1994, box 1, six males (PCL 11.0–14.0 mm),
76 females (PCL 10.6–16.2 mm), MNHN-Na; same data, four
females (PCL 14.9–17.7 mm); dive 24, site Eiffel Tower,
37°17.18#N, 32°16.29#W, 1,690 m, June 30, 1994, one female
(PCL 21.5 mm), CBM-ZC 9391; same data, one ovigerous
female (PCL 16.5 mm), MNHN-Na 16568; dive 25/936, 1,700
m, June 1, 1994, eight males (PCL 10.0–13.4 mm), nine females
(PCL 11.6–13.2 mm), MNHN-Na. PICO (DS Nautile): dive
1271, 37°17.646#N, 32°16.888#W, 1,643 m, August 8, 1998;
slurp gun 5, one female (PCL 14.8 mm), MNHN-Na 16569;
same data, five females (PCL 10.1–16.1 mm); same data, three
males (PCL 10.0–11.5 mm), six females (PCL 8.1–15.3 mm),
two juveniles (PCL 6.1, 6.3 mm). ATOS (ROV Victor): dive
119–17, 37°17.33#N, 32°16.63#W, 1,689 m, July 17, 2001, slurp
gun 7, 41 males (PCL 9.2–14.1 mm), 32 females (CL 11.5-ca
16.0 mm; larger specimens dissected for physiological study),
MNHN-Na 16571; same data, two males (PCL 10.1, 15.3
mm), one female (PCL 9.0 mm), CBM-ZC 9392. EXOMAR
(ROV Victor 6000): dive 269–20, 37°17.33#N, 32°16.52#W,
1,692 m, August 26, 2005, slurp gun 3, nine males (PCL 7.8 –
12.5 mm), 12 females (PCL 7.6–14.4 mm), three juveniles (PCL
4.8–6.0 mm), MNHN-Na 16572. MOMARETO (ROV Victor
6000): dive 294-11, site Eiffel Tower, 37°17.34#N, 32°16.53#W,
1,692 m, slurp gun 4, three females (PCL 11.1–11.2 mm),
MNHN-Na 16573.
Rainbow
ATOS (ROV Victor 6000): dive 107-05, site Iris 13,
36°13.80#N, 33°54.20#W, 2,289 m, 30.06.2001, slurp gun 3, seven
females (PCL 11.8–14.6 mm), MNHN-Na 16570.
TAG
EXOMAR (ROV Victor 6000): dive 260-11, 26°08.22#N,
44°49.56#W, 3626 m, August 13, 2005, slurp gun 3, one female
(PCL 11.9 mm), 10 juveniles (PCL 5.5–7.4 mm), MNHN-Na
16574; same dive, slurp gun 5, four males (PCL 9.5–11.5 mm),
10 females (PCL 7.3–16.4 mm), CBM-ZC 9393; dive 262-13,
26°08.20#N, 44°49.55#W, 3,642 m, August 15, 2005, slurp gun 2,
two males (PCL 6.3, 8.2 mm), four females (PCL 9.0–10.2 mm),
one juvenile (PCL 5.6 mm), MNHN-Na 16575; same dive, slurp
gun 4, four males (PCL 7.4–11.8 mm), two females (PCL 13.2,
17.0 mm), three juveniles (PCL 5.0–5.6 mm), MNHN-Na
16576.
Snake Pit
HYDROSNAKE (DS Nautile): HS 08, site Les Ruches,
23°22#N, 44°57#W, 3,478 m, 26 June 1988: 13 males (PCL 11.5–
15.4 mm); same data, four males (PCL 12.6–17.4 mm; dissected
for physiological study), MNHN-Na 11,871. DiversExpedition
(DS Alvin): dive 3672, 23°22.10#N, 44°56.91#W, 3,492 m, July
14, 2001, six juveniles (PCL 4.8–6.1 mm), MNHN-Na.
Figure 11. Chorocaris chacei (Williams & Rona, 1986). Juvenile (PCL 5.2 mm), Snake Pit, MNHN-Na. (A) Anterior part of carapace and cephalic
appendages, dorsal view; (B) same, lateral view; (C) posterior part of telson, dorsal view; (D) left second pereopod, lateral view; (E) left third pereopod,
lateral view.
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Logatchev
DiversExpedition (DS Alvin): dive 3666, July 6, 2001, one
female (PCL 13.5 mm), MNHN-Na 16577; dive 3668,
14°45.32#N, 44°58.79#W, 3,028 m, July 8, 2001, two males
(PCL 6.8, 7.0 mm), two females (PCL 7.7, 8.6 mm), two juve-
niles (PCL 5.2, 6.7 mm), MNHN-Na 16578; no station data,
80 juveniles (CL 4.3–7.3 mm), MNHN-Na. SERPENTINE,
dive 315– 06, Irina 2, 14°45.18#N, 44°58.74#W, 3,021 m, March
18, 2007, slurp gun 5, one juvenile (CL 5.0 mm), MNHN-Na
16704; dive 316-07, same site, March 20, 2007, slurp gun 4, 46
juveniles (CL 4.3–6.8 mm), MNHN-Na 16705.
Diagnosis
Spawning females. Rostrum (Fig. 9A, C) somewhat reduced
to broadly rounded lobe reaching or slightly overreaching
anterior margins of eye-stalks or antennal lobes, directed
downward; ventral surface slightly convex or flat. Carapace
(Fig. 9A to D) with anterior part sloping anteriorly; no
longitudinal depression on either side of midline; antennal lobe
broadly rounded; pterygostomial expansion directed rather
ventrally, exceeding beyond tip of antennal basicerite, rounded.
Antennae (Fig. 9C, D) suboperculate, strongly directed down-
ward, angle against horizontal line about 30–45°; distolateral
tooth subacute or blunt, clearly separated from lamella by
V-shaped notch. Scaphognathite of maxilla and caridean lobe
of first maxilliped bearing numerous plumose seta-like structure
on ventral surface; exopodal flagellum on first maxilliped com-
pletely reduced. First pereopod polymorphic (Fig. 10C, D).
Uropodal protopod (Fig. 9E) with posterolateral projection
subtriangular with subacute tip.
Non-spawning females and males. Rostrum (Fig. 10B)
bluntly triangular, overreaching anterior margins of eye-talks
or tips of antennal lobes by less than half of its length; ventral
surface slightly convex. Carapace (Fig. 10A, B) with broadly
triangular or rounded antennal lobe, tip subacute or blunt:
pterygostomial lobe directed forward, broadly rounded, less
produced. Antennae (Fig. 10A, B) normal, only slightly directed
downward. Lateral lobule of endopod of male first pleopod
slightly produced (Fig. 10F). Appendix masculina (Fig. 10G)
straight, 4 or 5 spiniform setae restricted to tip.
Description
See Williams and Rona (1986; as Rimicaris).
Size
Ovigerous female PCL 16.5 mm; males PCL 6.3–17.4 mm.
The largest specimen is a female PCL 21.5 mm, TL ca. 76 mm.
Variation
We have found that the conformation of the anterior part of
the carapace, including the rostrum, and antennae shows sub-
stantial ontogenetic change in adult Chorocaris chacei. The
rostrum is reduced in size in the spawning females. The
antennae are suboperculiform in spawning females, although
they are normal in males and nonspawning females. The chela
of the first cheliped can be robust in large specimens, but the
variation does not show correlation to sex; large specimens do
not always have robust chelae.
Komai and Segonzac (2006) showed a female specimen from
Lucky Strike, of which the rostrum, antennal lobe, and
pterygostomial expansion terminate in an acute tooth. Among
the specimens examined in this study, one male specimen from
Lucky Strike also has acutely pointed rostrum and antennal
lobe (Fig. 8F, G). We consider that these specimens represent
an aberrant form of the species.
Distribution
Mid-Atlantic Ridge: Snake Pit (23°N), TAG (26°N), Lucky
Strike (37°17#N), and Logatchev vent field, 1,600–3,650 m.
Remarks
As noted before, small paratypic specimens of Chorocaris
chacei (five specimens of USNM 228454 and one specimen of
MNHN-Na 10535) are the stage B juvenile of Rimicaris
exoculata.
As mentioned earlier, three species of Chorocaris are very
similar for one another. Characters useful for species discrim-
ination are often affected by ontogenetic or individual varia-
tion. Spawning females of C. chacei can be rather easily
distinguished from those of C. vandoverae and C. paulexa by
the reduced rostrum, the lack of submedian longitudinal
depressions on the dorsal surface of the carapace, and the
broadly rounded antennal lobe of the carapace. In the latter two
species, spawning females have submedian depressions on the
dorsal surface of the carapace, more developed rostrum and
clearly delineated antennal tooth. However, it is not easy to
morphologically differentiate males and nonspawning females
of the three species because of variation. Nevertheless, the
distolateral tooth of the antennal scale appears more strongly
reduced in C. vandoverae than in C. chacei and C. paulexa.InC.
vandoverae, the distolateral tooth is blunt and strongly approx-
imated to the distal lamella. In contrast, in C. chacei and C.
paulexa, the distolateral tooth is subacute or blunt and is clearly
separated from the lamella by a V-shaped notch. In general,
males and nonspawning females of C. chacei differs from those
of C. vandoverae and C. paulexa in the broadly rounded
pterygostomial projection. In the latter two species, the pter-
ygostomial projection tapers distally. With regard to males, C.
chacei can be distinguished from C. vandoverae by the armature
of the appendix masculina. In C. chacei, the appendix masculina
is armed with four or five terminal or subterminal spines,
whereas in C. vandoverae, it bears numerous spines including
one or two rows extending onto the dorsal surface. No
information on male morphology is available for C. paulexa.
Furthermore, the available material suggests that C. chacei
attains maturity at size fairly larger than C. vandoverae and C.
paulexa. Ovigerous specimen(s) are PCL 16.5 mm in C. chacei,
PCL 6.9–11.7 mm in C. vandoverae,andPCL9.6mmin
C. paulexa. In addition, the largest female is PCL 17.4 mm in
C. chacei, PCL 13.4 mm in C. vandoverae and PCL 9.6 mm in C.
paulexa.
Martin and Hessler (1990) cited the size of the carpal
grooming apparatus of the first pereopod (as cleaning brush)
and the shape of the antennular stylocerite in discriminating
C. vandoverae from C. chacei. However, these two characters
are difficult to use because of the intraspecific variability in both
species.
Chorocaris vandoverae Martin and Hessler 1990 (Fig. 12)
Chorocaris vandoverae Martin and Hessler 1990: 2, Figures 1,
2, 3 a to e; Shank 1997:194; Shank et al. 1999: 246 (Table 1),
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247 (Table 2); Martin and Shank 2005: 184; Martin and Haney
2005: 465; Komai and Segonzac 2006: 423, Figures 1–4.
Type Material
Holotype. Mariana Back Arc Basin. DSV Alvin,dive
1843, Alice Spring vent field, 18°12.599#N, 144°42.231#E,
3,640 m, May 4, 1987, female (PCL 13.4 mm), USNM
243946.
Paratypes: Same data as holotype, 10 females (PCL 8.0–
12.6 mm), USNM 243947.
Other Material
Mariana Back Arc Basin. DSV Shinkai 6500, dive 355, Alice
Springs vent field, 18°12.8#N, 144°42.4#E, 3,600 m, July 7, 1996,
two males (PCL 5.8, 8.0 mm), four nonovigerous females (PCL
4.9–7.9 mm), six ovigerous females (PCL 6.9–11.7 mm), JAMSTEC
004961–004972.
Diagnosis
Rostrum (Fig. 12A to C) large, bluntly triangular or
rounded, overreaching eye-stalks or antennal tooth by 0.2–0.5
of its length; ventral surface notably convex. Carapace (Fig.
12A to C) with anterior part not strongly sloping anteriorly
even in spawning females; shallow longitudinal depressions,
ornamented with irregular pattern of longitudinal striae, pre-
sent on dorsal surface either side of midline in ovigerous
females; antennal tooth showing as small, blunt prominence;
pterygostomial projection directed forward, somewhat tapering
distally, reaching tip of ventrolateral tooth of basicerite,
terminating in rounded tip. Antennae (Fig. 12B, C) not strongly
operculiform, slightly directed downward, angle against hori-
zontal plane of carapace 10–15°; distolateral tooth blunt,
closely approximated to lamella, thus apparently inconspicu-
ous. Scaphognathite of maxilla and caridean lobe of first
maxilliped lacking plumose seta-like structure on ventral sur-
faces; exopodal flagellum of first maxilliped showing as small
triangular process practically obscured by dense setae. First
Figure 12. Chorocaris vandoverae Martin & Hessler, 1990. (A–C, F) Ovigerous female (PCL 12.0 mm), JAMSTEC 004961–004982, Alice Springs
Field, Mariana Back Arc Basin; (D, E) male (cl mm), same lot. (A) Carapace, dorsal view; (B) anterior part of carapace and cephalic appendages, lateral
view; (C) same, dorsal view; (D) endopod of left first pleopod, ventral view; (E) appendices interna and masculina of left second pleopod, mesial view;
(F) protopod of left uropod, dorsolateral view. Scale bars: 5 mm for A; 2 mm for B, C; 1 mm for F; 0.5 mm for E.
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pereopod apparently nonpolymorphic. Distolateral lobe of
endopod of first pleopod not delineated (Fig. 12D). Appendix
masculina (Fig. 12E) slightly curved, with more than 10 spini-
form setae extending beyond midlength on dorsomesial margin.
Uropodal protopod with posterolateral projection suboval
(Fig. 12F).
Description
See Martin and Hessler (1990).
Size
Ovigerous females PCL 6.9–11.7 mm; males PCL 5.8–8.0 mm.
The largest specimen is a female PCL 13.4 mm, TL ca. 48 mm.
Variation
Spawning females have shallow submedian depressions on
the dorsal surface of the carapace, which are not present in
males and nonspawning females.
Distribution
So far known only from Alice Springs and Burke vent fields,
Mariana Back-Arc Basin, western Pacific, 3,640–3,660 m.
Remarks
Chorocaris vandoverae appears closest to C. paulexa. Differ-
ences between the two species are discussed under the account
of the latter species.
Chorocaris paulexa Martin and Shank 2005 (Fig. 13)
Chorocaris paulexa Martin and Shank 2005: 186, Figures 1–8;
Martin and Haney 2005: 464; Komai and Segonzac 2006:
422, Figures 1–3.
Type material
Holotype: Southern East Pacific Rise. DSV Alvin: dive 3296,
Rapa Nui Homer vent site, 17°37.220#S, 113°15.123#W, 2,596
m, October 27, 1998, Hoover slurp, ovigerous female (PCL 7.5
mm), LACM CR 1998-151.1.
Paratype: Same data as holotype, one female (PCL 9.6 mm),
LACM CR 1998.151.2.
Diagnosis
Rostrum (Fig. 13A, B) bluntly triangular, overreaching
eye-stalks or antennal lobes by half of its length; ventral
surface convex. Carapace (Fig. 13A, B) with anterior part
slightly sloping anteriorly; shallow longitudinal depressions,
ornamented with irregular pattern of minute longitudinal
striae, present on dorsal surface either side of midline in
ovigerous female; antennal tooth showing as blunt prominence;
pterygostomial expansion not reaching tip of ventrolateral
tooth of antennal basicerite, triangular, terminating in subacute
tip. Antennae (Fig. 13B) not operculiform, slightly directed
downward, angle against horizontal plane of carapace less than
10°; distolateral tooth subacute, distinctly separated from
lamella by V-shaped notch. Scaphognathite of maxilla and
caridean lobe of first maxilliped lacking plumose seta-like
structure on ventral surfaces; exopodal flagellum of first
maxilliped showing as small triangular process. First pereopod
apparently nonpolymorphic. Male unknown. Uropodal proto-
pod with posterolateral projection triangular with subacute tip
(Fig. 13C).
Description
See Martin and Shank (2005).
Size: Ovigerous female PCL 7.5 mm, males unknown.
Figure 13. Chorocaris paulexa Martin & Shank, 2005. Holotype, ovigerous female (PCL 7.7 mm), LACM CR 1998–151.1, Homer Vent, southern East
Pacific Rise. (A) Carapace, dorsal view; (B) anterior part of carapace and cephalic appendages, lateral view; (C) protopod of left uropod, dorsolateral
view. Scale bars: 2 mm for A; 1 mm for B, C.
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Variation
The single ovigerous female has shallow submedian depres-
sions on the dorsal surface of the carapace, whereas the non-
ovigerous female lack such depressions.
Distribution
So far known only from hydrothermal vent sites on the
southern East Pacific Rise (17°–21°S), 2,573–2,832 m (Martin &
Shank 2005).
Remarks
Chorocaris paulexa differs from C. vandoverae in the sub-
acutely pointed pterygostomial projection of the carapace and
subacutely pointed posterolateral projection of the uropodal
protopod. In C. vandoverae, the pterygostomial projection is
distally rounded; and the posterolateral projection of the
uropodal protopod is bluntly pointed usually. The rostrum is
comparatively smaller in C. paulexa than in C. vandoverae (Fig.
13A and 12A). The distolateral tooth of the antennal scale is
clearly separated from the lamella in C. paulexa, rather than
closely approximated to the lamella in C. vandoverae.
BIOGEOGRAPHY
Five species treated in this study constitute a monophyletic
assemblage within Alvinocarididae. The general geographical
range of this assemblage is widespread in the world oceans,
although the range of each species is restricted to a particular
area. Rimicaris exoculata and Chorocaris chacei have a wide
longitudinal distribution along the Mid-Atlantic Ridge, and the
former has been recorded from 37°Nto4°S, and the latter from
37°Nto14°N. The other three species are restricted to narrow
areas. Rimicaris kairei is known only from two vent fields
(Kairei & Edmond) at the Rodriguez Triple Junction of the
Central Indian Ridge, Indian Ocean. Chorocaris vandoverae is
known from Burke and Alice Springs fields on the Mariana
Back Arc Basin, northwestern Pacific Ocean. Chorocaris pau-
lexa is so far limited to the Easter Microplate area on the
southern East Pacific Rise. The two Rimicaris species are
distributed in the Atlantic and Indian Oceans respectively,
and the possible sister species of the Rimicaris clade, C. chacei,
occurs in the Atlantic Ocean. Other two species of Chorocaris,
C. vandoverae, and C. paulexa, occur in the western and eastern
Pacific, respectively. It is remarkable that species referable to
Chorocaris has not been collected from the Indian Ocean,
whereas species referable to Rimicaris has not been found in
the Pacific Ocean in spite of recent active surveys. Such
distributional pattern would seem to suggest that these taxa
are relicts, but Shank et al. (1999) argued that vent shrimps
comprise the youngest vent- and seep-associated diversification
observed to date.
ACKNOWLEDGMENTS
The authors are indebted to the chief scientists of various
cruises and the crews of ROV Victor 6000 and those of RVs
L’Atalante and Pourquoi Pas? for collecting specimens used in
this study: Anne Godfroy (Ifremer; cruise EXOMAR), Joze
´e
Sarrazin and Pierre-Marie Sarradin (Ifremer; cruise MoMARETO),
and Yves Fouquet (Ifremer, cruise SERPENTINE). The
authors thank Angelica Brandt and Olav Giere (ZMH), Patrick
Briand (Ifremer), Re
´gis Cleva and Alain Crosnier (MNHN),
Rafael Lemaitre (USNM), Joel W. Martin (LACM) and Shinji
Tsuchida (JAMSTEC) for the loan of the specimens. At the
Paris Museum the senior author sincerely thank R. Cleva and
A. Crosnier for access to collections as well as help in many
matters. The cruise MOMARETO was partially funded by the
European project EXOCET/D (GOCE-CT-2003-505342).
SERPENTINE cruise was partially funded by the French
ANR ‘‘Deep Oasis.’’
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