A New Caridean Shrimp of the Family Alvinocarididae from Thermal Vents at Menez Gwen on the Mid-Atlantic Ridge
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23 April 2003 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 1I6(1):I58-I67. 2003. A new caridean shrimp of the family Alvinocarididae from thermal vents at Menez Gwen on the Mid-Atlantic Ridge Timothy M. Shank and Joel W. Martin (TMS) Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, U.S.A., e-mail: [email protected]; (JWM) Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, California 90007, U.S.A., e-mail: [email protected] Abstract.—A new species of alvinocaridid shrimp, Alvinocaris williamsi, is described from the Menez Gwen hydrothermal vent field on the Mid-Atlantic Ridge. The new species is most similar to another relatively shallow water alvinocaridid, A. stactophila Williams, known only from a cold seep area off the coast of Louisiana, but differs in details of the rostrum and appendages. Alvinocaris williamsi is also morphologically similar to two species of the genus recently described from the Mid-Okinawa Trough, Japan. Molecular phy- logenetic studies of A. williamsi, the eighth described member of the genus, may provide significant insights into the role that deep-sea hydrothermal vents at mid-ocean ridges and hydrocarbon seeps on continental margins have played in the evolution of fauna endemic to these chemosynthetic habitats. The caridean shrimp family Alvinocari The type genus of the Alvinocarididae, didae was originally proposed by Christof- Alvinocaris, is the most diverse genus of fersen (1986) to accommodate a number of the family and contains five hydrothermal morphologically similar shrimp known vent-endemic species: A. brevitelsonis Kik- from hydrothermal vents and hydrocarbon uchi & Hashimoto, 2000, from the Minami- seeps. The family was further diagnosed by Ensei Knoll in the Mid-Okinawa Trough off Segonzac et al. (1993) in a footnote, and Japan; A. leurokolos Kikuchi & Hashimoto, also by Vereshchaka (1996a, 1996b, 1997) 2000, also from the Minami-Ensei Knoll; A. (see Martin & Davis 2001). To date, five longirostris Kikuchi & Ohta, 1995, from genera have been proposed for the family. the Iheya Ridge off Japan; A. lusca Wil In the order in which they were proposed, liams & Chace, 1982, from the Galapagos they are: Alvinocaris Williams & Chace, Rift in the eastern Pacific; and A. markensis 1982; Rimicaris Williams & Rona, 1986; Williams, 1988, from the Mid-Atlantic Chorocaris Martin & Hessler, 1990; Opae- Ridge. Another two species of Alvinocaris pele Williams & Dobbs, 1995; and lorania are endemic to chemosynthetic habitats as Vereshchaka, 1996b (see Shank et al. 1998 sociated with hydrocarbon and brine seeps: for the synonymy of lorania and Rimicar A. muricola Williams, 1988, from the West is). A sixth genus of vent shrimp, Mirocaris Florida Escarpment; and A. stactophila Wil Vereshchaka, 1997, was proposed by Ver liams, 1988, from the Louisiana Slope in eshchaka (1997) for Chorocaris fortunata the northern Gulf of Mexico. The study of Martin & Christiansen (1995) and for a new additional collections, including unde- species (M. keldyshi Vereshchaka, 1997); scribed hydrothermal-associated shrimp however, this genus was transferred to the specimens from the Edison Seamount of the newly created family Mirocarididae by Ver Bismark Archipelago in Papua New Guinea eshchaka (1997). (Shank et al. 1999; K. Baba, pers. comm.). VOLUME 116, NUMBER I 159 from the Logatchev vent field of the Mid- portion of a hydrothermally-active mussel Atlantic Ridge (A. Vereshchaka, pers. bed community that included a more abun comm.), and several recently recovered dant alvinocaridid species, Mirocaris keld- from active seamounts north of the Bay of yshi, amphipods, Luckia striki Bellan-San- Plenty (northern North Island, New Zea tini & Thurston, gastropods, e.g., Lepeto- land) (Rick Webber and Neil Bruce, pers. drilus spp. and Protolira valvatoides Waren comm., http;//www.niwa.co.nz/pubs/bu/05/ & Bouchet, polychaetes, e.g., Branchipo- blind) may yield additional new species of lynoe seepensis Fettibone, and crabs, S«?- Alvinocaris. The pan-equatorial biogeo gonzacia mesatlantica (Williams, 1988) graphic distribution of the genus is note and Chaceon affinis (A. Milne-Edwards & worthy. Alvinocaris species occur in almost Bouvier, 1894). Specimens were brought to every biogeographic vent province (except the surface in an insulated container and the Northeast Pacific vents; Shank et al. placed in chilled water on-board ship. 1999). However, recent initial investiga Whole shrimp were sorted by morphotype tions of hydrothermal vents in the Indian and either preserved in 4% buffered for Ocean did not reveal the presence of Alvi malin in seawater and subsequently trans nocaris shrimp despite the common ap ferred to 70% ethanol or frozen at — 70°C pearance of the other dominant Atlantic and and subsequendy transported on dry ice and Pacific genera Rimicaris and Chorocaris stored at -80°C. Carapace length (CL) of (Hashimoto et al. 2001, Van Dover et al. each individual was measured in millime 2001). The Alvinocaris species described ters (mm) from the orbital margin to the herein occupies the northernmost extent of posteriomedial margin of the carapace. We the generic range, as it inhabits the Menez recognize that the description of new spe Gwen vent site, the most shallow vent field cies within this family from relatively few (850 m) and the most northern known ac individuals can be risky (see Shank et al. tive deep-sea hydrothermal site along the 1998); however, preliminary results of mi Mid-Atlantic Ridge {37°50.5'N, 3l°3l3'W) tochondrial DNA sequence data (Shank, (Gebruk et al. 1997, Colago et al. 1998, pers. obs.) complement morphological evi Comtet & Desbruyeres 1998, Desbruyeres dence that distinction of this species from et al. 2001). Below, we describe a new spe other Alvinocaris species is warranted. The cies of Alvinocaris from the Menez Gwen holotype and paratypes are deposited in the hydrothermal vent field, and suggest evo collections of the National Museum of Nat lutionary relationships with other alvino- ural History, Smithsonian Institution, carid species. Washington, D.C. (USNM). The remaining specimens are cryo-preserved at the Woods Hole Oceanographic Institution for ongoing Materials and Methods molecular phylogenetic investigations by All specimens were collected using the TMS. human occupied submersible DSV Alvin at the Menez Gwen hydrothermal vent field, northern Atlantic Ocean. Shrimp were col Alvinocaris williamsi, new species lected from a cluster of active individuals Figs. 1-3 among clumps of mussels, Bathymodiolus azoricus Von Cosel, Comtet & Krylova, Material examined.—14 females CL: 8.2, within vent flow with a 30 cm X 30 cm 8.2, 8.5, 8.7, 8.9, 8.9, 9.3, 9.5, 9.5, 9.5, 9.6, square "black net" (BN) operated using the 9.6, 9.7, 10. L DSV Alvin, Dive 3117, Menez manipulator arm by the pilots oi DSV Alvin. Gwen hydrothermal vent field, North Atlan A total of 14 specimens were collected tic Ocean, 37°50.5'N, 3r31.3'W, 850 m, 7 (from a single net sample) from areas of Jul 1997. most intense diffuse fluid within the central Types.—All from DSV Alvin Dive 3117. 160 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Fig. L Alvinocaris williamsi, new species, iiolotype ovigerous female, USNM 1009651. a, body, cephalic appendages, and abdomen, lateral view; b, anterior region of carapace, including eyes and antennae, dorsal view; c, telson and uropods, dorsal view. Scale bars equal 1.0 mm (bar 1 for a, bar 2 for b, bar 3 for c). Holotype: adult female CL 9.5 mm, ovig midlength of second segment; dorsal mar erous (specimen ID: BN 70), USNM gin raised into thin serrate crest containing 1009651. Paratypes: 2 adult females CL 13 or 14 teeth of nearly equal strength in 9.3, 9.7 (specimen ID: BN 68 and BN 51, central sector of row, about 0.5 length of respectively), abdomen torn from body, tail crest continued onto carapace, deflecting fan missing, USNM 1009652, USNM from dorsal line of carapace at approximate 1009653. 45° angle; ventral margin less prominent, Description.—Integument thin, shining, straight, and unarmed or with 1 minute sub- minutely punctuate. Rostrum (Fig. la, b) al terminal tooth; lateral carina (not visible in most straight, imperceptibly elevated above Fig. la) broadened proximally and conflu horizontal in distal half; sharply pointed tip ent with orbital margin. Carapace (Fig. la) (broken or slightly blunted in all speci with buttressed and distinct antennal spine; mens) reaching at least to level of articu pterygostomian spine prominent, acumi lation between first and second peduncular nate. Anterior antennal carina curving pos- segment of second antenna or sometimes to teroventrally from near base of antennal VOLUME 116. NUMBER 1 161 spine to intersect at about midlength of car with stronger mesiodistal spine. Antennal apace with carina extending posteriorly scale (scaphocerite) broadly rounded distal- from pterygostomial spine, its associated ly, with broad triangular tooth on distola- groove (not visible in Fig. lb) continuing teral border extending to same level as indistinctly posteriorly. rounded distal border. Abdomen of female broadly arched dor- Mouthparts (Fig. 2) fairly typical for the sally, gradually tapering posteriorly, height genus. Mandible (Fig. 2a, b) with 6 blunt, of sixth somite about half that of first so uneven, terminal teeth plus one slightly mite. Pleura of third somite broadly round sharper dorsal subterminal tooth along cut ed, that of fourth somite irregularly round ting border, and with long, blunt, posterior ed, flanked dorsally by single remote ob tooth ("molar process" of some authors) solescent spine; fifth pleuron with strong separated from cutting edge by a wide gap; acute triangular posteroventral tooth mandible deeply excavate on internal (pos flanked dorsally by cluster of 2 or 3 remote terior) surface just above this blunt poste small spines on margin; sixth somite with rior tooth; mandibular palp 2-segmented, middorsal length about 1.4-1.9 that of fifth distal article bearing numerous plumose se somite, broad-based posterolateral tooth tae; basal article with 2 plumose setae on overlapping base of telson.