Alvinocaris solitaire, Yahagi & Watanabe & Kojima & Beedessee & Komai, 2014

Yahagi, Takuya, Watanabe, Hiromi, Kojima, Shigeaki, Beedessee, Girish & Komai, Tomoyuki, 2014, First record and a new species of Alvinocaris Williams & Chace, 1982 (Crustacea: Decapoda: Caridea: Alvinocarididae) from the Indian Ocean, Zootaxa 3893 (1), pp. 101-113 : 103-111

publication ID	https://doi.org/ 10.11646/zootaxa.3893.1.4
publication LSID	lsid:zoobank.org:pub:BA1722A9-9D84-403D-B278-D0CBF0C87C7A
persistent identifier	https://treatment.plazi.org/id/1C7487EA-6B6F-FFE8-FF2B-F9D27AA1FC59
treatment provided by	Felipe
scientific name	Alvinocaris solitaire
status	sp. nov.

Treatment

Alvinocaris solitaire View in CoL sp. nov.

( Figs. 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Material examined. Holotype: RV “Yokosuka”, YK 13-02 cruise, Central Indian Ridge , Solitaire hydrothermal vent field, HOV “Shinkai 6500”, dive 6K#1326, 19°33.413’S, 65°50.888’E, 2606 m depth, 10 February 2013, male (cl 14.1 mm), NSMT-Cr 23748. GoogleMaps

Description. Body ( Fig. 1 View FIGURE 1 ) moderately slender; integument thin, surface almost glabrous, shining.

Rostrum ( Fig. 2A, B View FIGURE 2 ) directed forward, nearly straight, but distal part slightly bent, 0.60 of carapace length, slightly reaching beyond distal margin of second segment of antennular peduncle; dorsal margin nearly straight, armed with 16 teeth, including 9 teeth on rostrum proper and 7 teeth on carapace posterior to orbital margin, posteriormost tooth arising at 0.45 of carapace length (most of postrostral teeth broken at tips); ventral margin armed with 2 teeth in anterior 0.30; lateral carina distinct in proximal half, merging into orbital margin.

Carapace ( Figs. 1 View FIGURE 1 , 2A, B View FIGURE 2 ) with postrostral median ridge relatively low, extending to 0.70 of carapace length, dorsal angle approximately 165°. Carapace width 0.58 of length. Orbital margin evenly concave. Antennal tooth moderately strong; pterygostomial tooth relatively small, not exceeding beyond antennal tooth. Post-antennal groove shallow; branchial region not particularly inflated.

Eighth thoracic sternite with long median spur directed anteroventrally.

Pleon ( Fig. 1 View FIGURE 1 ) rounded dorsally. First and second pleura unarmed marginally; third pleuron with 4 (right) and 6 (left) slender teeth on posterolateral margin ( Fig. 2C, D View FIGURE 2 ); fourth pleuron with relatively strong posteroventral tooth and additional 3 (right) and 5 (left) on posterolateral margin and 2 tiny denticles on ventral margin ( Fig. 2C, D View FIGURE 2 ); fifth pleuron with strong posteroventral tooth and 3 additional small, slender teeth on posterolateral margin ( Fig. 2C, D View FIGURE 2 ). Sixth abdominal somite 1.62 times longer than high, with small but distinct posteroventral tooth.

Telson ( Fig. 2E View FIGURE 2 ) not reaching posterior margin of uropodal endopod, length 3.20 times anterior width and 4.15 times posterior width; armed with 7 dorsolateral spines on either side; posterior margin ( Fig. 2F View FIGURE 2 ) medially shallowly concave, armed with 5 pairs of upturned spines (mesial spines unequal in length), no plumose setae medially.

Eyes ( Fig. 2A, B View FIGURE 2 ) fused mesially; corneas globular, unfaceted, and unpigmented; demarcation between corneal region and stalk unclear; small spiniform tubercle on anterodorsal surface, directed upward.

Antennular peduncle ( Fig. 2A, B View FIGURE 2 ) moderately stout, reaching beyond distal margin of antennal scale. First segment with conspicuous proximal tubercle on dorsal surface laterally and strong distolateral tooth; dorsal surface with distinct longitudinal groove; stylocerite sharp, reaching to distal 0.25 of second segment. Second segment 1.95 times longer than wide, with small distomesial tooth. Lateral flagellum ( Fig. 1 View FIGURE 1 ) longer than carapace; mesial flagellum somewhat longer than lateral flagellum.

Antenna ( Fig. 2A, B, G View FIGURE 2 ) with stout basicerite bearing moderately strong ventrolateral and weak ventral teeth. Carpocerite stout, not reaching mid-length of antennal scale. Antennal scale about half length of carapace, 2.10 times longer than wide; lateral margin nearly straight; middorsal ridge on dorsal surface slightly diverging against lateral margin; distolateral tooth fairly strong, directed forward, falling short of broadly rounded distal margin of blade.

Mouthparts typical of genus (cf. Komai & Segonzac 2005). Mandible ( Fig. 3A View FIGURE 3 ) with incisor process bearing 8 marginal teeth in left; molar process slender, rounded tip minutely setose; palp bi-articulated. Maxillule ( Fig. 3B View FIGURE 3 ) with endopod bearing 2 minute setae on ventral surface of external lobe, internal lobe with 1 apical setulose seta. Maxilla ( Fig. 3C View FIGURE 3 ) without distinctive features. First maxilliped ( Fig. 3D View FIGURE 3 ) without trace of flagellum on moderately broad exopod; endopod bi-articulated, distal article very short ( Fig. 3E View FIGURE 3 ). Second maxilliped ( Fig. 3F View FIGURE 3 ) with endopod moderately stout; epipod subtriangular, with non-lamellate, rod-like podobranch.

Third maxilliped ( Fig. 4A View FIGURE 4 ) overreaching antennal scale by about half length of ultimate segment. Ultimate segment distinctly longer than penultimate segment (= carpus), trigonal in cross section, tapered distally, bearing 2 terminal spines; lateral surface longitudinally carinate, with row of setae; ventromesial surface flat, with rows of dense setae. Antepenultimate segment (fused merus, ischium and basis) flattened dorsoventrally, sinuously curved in dorsal view, bearing long marginal setae and 1 slender spine at ventrolateral distal angle. Coxa stout; epipod directed laterally, slightly bi-lobed.

First pereopod ( Figs. 4B View FIGURE 4 , 5A, B View FIGURE 5 ) reaching mid-length of ultimate segment of third maxilliped, moderately robust. Fingers elongate, curved downward and inward, opposable edges each armed with comb-like row of uniform teeth close-set against one another, teeth of fixed finger somewhat longer than those on dactylus; dactylus 4.7 times as long as palm; fixed finger; palm very short, slightly inflated, without patch of grooming setae. Carpus cup-like, 3.0 times as long as palm, distal half of flexor surface flared into prominent lateral ridge ending in strong tooth; mesial surface shallowly excavated, with grooming apparatus consisting of patch of short setae. Merus and ischium unarmed, somewhat flattened.

Second pereopod ( Figs. 4C View FIGURE 4 , 5C View FIGURE 5 ) shorter and more slender than first, reaching mid-length of antennal scale; fingers subequal to in length to palm, curved distally and cross each other when closed, each terminating in acute corneous unguis; no hiatus between fingers; opposable margins each pectinated with single row of minute corneous teeth. Carpus longer than chela. Merus and ischium obliquely articulated in lateral view; ischium armed with 1 spine ventrolaterally.

Third to fifth pereopods moderately slender, generally similar in structure but propodi becoming progressively longer from third to fifth. Third pereopod ( Fig. 4D View FIGURE 4 ) overreaching distal margin of antennal scale by half length of propodus; dactylus ( Fig. 5D View FIGURE 5 ) short, armed with single row of 4 accessory spinules on flexor margin and clearly demarcated unguis; propodus with slender spinules arranged in 2 rows on ventral surface; carpus shorter than propodus, unarmed; merus with 3 spines on lateral surface ventrally; ischium with 2 spines on lateral surface ventrally. Fourth pereopod ( Fig. 4E View FIGURE 4 ) overreaching distal margin of antennal scale by 0.20 length of propodus; merus armed with 3 spines; ischium with 2 spines. Fifth pereopod ( Fig. 4F View FIGURE 4 ) slightly reaching beyond distal margin of antennal scale by tip of propodus; propodus with numerous spiniform setulose setae on ventral surface, arranged in 3 or 4 longitudinal rows; merus spineless; ischium with 2 spines.

Male first pleopod ( Fig. 5E, F View FIGURE 5 ) with endopod having relatively broad, distally narrowing distomesial lobe bearing 6 spiniform setae directed mesially or distomesially on mesial margin and 4 simple stiff setae on lateral margin; lateral margin of endopod proper proximal to base of distomesial lobe gently convex, with row of plumose setae; mesial margin faintly sinuous, with row of stiff setae including 4 simple stiff setae in distal half, other setae plumose. Appendix masculina on second pleopod ( Fig. 5G, H View FIGURE 5 ) shorter than appendix interna, distally with 6 spiniform setae.

Uropods ( Fig. 2E View FIGURE 2 ) with both rami elongate oval. Exopod slightly longer than endopod, with small movable spine just mesial to smaller distolateral tooth; dieresis sinuous.

Coloration in life. Body ( Fig. 6 View FIGURE 6 ) whitish translucent. Eye light yellow with shiny reflection.

Distribution. Known only from the type locality, the Solitaire hydrothermal vent field, Central Indian Ridge, at a depth of 2606 m.

Remarks. Alvinocaris is typically characterized by a slender rostrum with dorsal teeth, the well-developed postrostral ridge extending beyond the mid-length of the carapace, the dorsolateral spines on the telson arranged in a linear row, the possession of a small spiniform tubercle on the anterior surface of the eye, the dactyli of the third to fifth pereopods bearing accessory spinules arranged in a single row, and the presence of meral spines on the third and fourth pereopods ( Komai & Segonzac 2005). The new species is assigned to Alvinocaris without hesitation on account of these characters.

Alvinocaris solitaire sp. nov. is morphologically most similar to A. lusca from the Galapagos Rift, East Pacific Rise in the shape and posterior armature of the telson: in both species, the telson is very slightly narrowed toward the posterior; the posterior margin is medially shallowly excavated and, armed with a row of spines. These two species are also similar in the length and armature of the rostrum, little elevated dorsum of the carapace and the general armature of the third to fifth pereopods. Nevertheless, the new species can be distinguished from A. lusca by some minor morphological differences ( Williams & Chace 1982; Komai & Segonzac 2005): in A. solitaire sp. nov., the pterygostomial tooth is weak, not exceeding the antennal tooth, whereas it is stronger and exceeds the latter in A. lusca ; the pleuron of the third pleomere is armed with small but conspicuous teeth on the posteroventral margin in the new species, rather than unarmed in A. lusca ; the posterior margin of the telson is devoid of setae medially in the new species, whereas there are a few short plumose setae on the medial part of the posterior margin in A. lusca .

Alvinocaris komaii is also similar to A. solitaire sp. nov. and A. lusca in the structure and armature of the telson, but it is readily distinguished from them by the stronger postrostral teeth on the carapace and the accessory spinules on the dactyli of the third to fifth pereopods arranged in two rows ( Zelnio & Hourdez 2009).

Two other congeners, Alvinocaris brevitelsonis known from the Minami Ensei Knoll in the Okinawa Trough, Japan, and A. stactophila from the Gulf of Mexico, also have a row of spines, instead of plumose setae, on the posterior margin of the telson. However, in these two species, the third pleuron is unarmed; the narrowing of the telson posteriorly is more pronounced; and the posterior margin of the telson is regularly convex, without median excavation ( Williams 1988; Kikuchi & Hashimoto 2000; Komai & Segonzac 2005). The new species differs further from A. brevitelsonis in having fewer rostral ventral teeth (2 versus 7). Alvinocaris solitaire sp. nov. contrasts with A. stactophila in the longer rostrum and arrangement of spines on the posterior margin of the telson.

The neighbor-joining (NJ) and maximum likelihood (ML) trees inferred from partial COI sequences (600 bp) for nine species of Alvinocaris , including the new species, are shown in Fig. 7 View FIGURE 7 .

Alvinocaris solitaire sp. nov. is clustered with a clade including A. markensis , A. muricola , A. longirostris and A. lusca with high bootstrap support (96% in both trees). Interspecific genetic divergence (K2P) among these nine species is summarized in Table 2. The mean value of genetic divergence observed within Alvinocaris was 0.135. The new species is closest to A. muricola and A. markensis genetically (0.112 and 0.114, respectively), although morphological characters do not support this close relationship. The genetic divergence between A. solitaire sp. nov. and A. lusca is 0.140, well supporting the differentiation of the two species. Alvinocaris dissimilis is most genetically divergent from A. solitaire sp. nov. (0.165). The maximum divergence within Alvinocaris is between A. lusca and A. komaii (0.206); A. komaii is clustered with the out-group species Rimicaris exoculata in the both trees, although the bootstrap support is weak (see also Zelnio & Hourdez 2009).

The new species represents the discovery of Alvinocaris from Indian-Ocean hydrothermal vents, despite extensive biological sampling in the area by previous expeditions ( Hashimoto et al. 2001, Van Dover et al. 2001, Nakamura et al. 2012).

Habitat and associated species. The present specimen was collected in an assemblage of white predatory gastropods of the genus Phymorhynchus , which is distributed in the periphery of an actively venting area in the Solitaire hydrothermal vent field. The alvinocaridid shrimp Mirocaris indica and some species of polychaetes (e.g. Archinome sp. ) and limpets (e.g. Eulepetopsis sp. ) were collected with A. solitaire sp. nov.

Etymology. Named after the type locality, Solitaire hydrothermal vent field; used as noun in apposition. The name of the hydrothermal vent field, “Solitaire”, was derived from an extinct species of an endemic bird (Rodriguez solitaire, Pezophaps solitaria ) inhabiting Rodriguez Island ( Nakamura et al. 2012).