Alvinocaris komaii Zelnio and Hourdez 2009

Alvinocaris komaii Zelnio and Hourdez, 2009 Alvinocaris komaii Zelnio and Hourdez, 2009: 55, figs. 1–6. Material examined

Non-type. Lau Basin. BIOLAU, BL 08, site Vailili, 23°13 ʹ S, 176°38 ʹ W, 1740 m, 18 May 1989, slurp gun, 1 male (cl 12.2 mm), MNHN; BL 10, same site, 22 May 1989, 1 female (cl 15.2 mm), CBM-ZC 11,956. North Fiji Basin. STARMER II, RV Kaiyo, dive 19, site White Lady, 18°50 ʹ S, 173°29 ʹ E, 2750 m, July 1989, 1 female (cl 14.6 mm), MNHN. Vanuatu. RV Sonne, SO 229-061-N202, Nifonea vent field, 18°07.735 ʹ S, 169° 31.018 ʹ E, 1871 m, 19 July 2013, 1 female (cl 19.5 mm), CBM-ZC 12,483.

Rostrum (Figure 15A–C) slender, terminating acutely, reaching or overreaching distal margin of first segment of antennular peduncle; dorsal margin sharply carinate, armed with row of teeth becoming larger posteriorly and extending beyond midlength of carapace (five postrostral teeth present); ventral ridge well developed, armed with one or more teeth; lateral carina conspicuous. Carapace (Figure 15A, B) with distinct postrostral carina extending beyond midlength; dorsal margin of carapace in lateral view gently arcuate, with peak at posteriormost tooth of dorsal rostral series; no longitudinal depression on either side of midline even in spawning females; antennal tooth acuminate; pterygostomial tooth strong, acuminate; anterior part of branchial region not strongly inflated; dorsal organ absent.

Third pleomere (Figure 15D) armed with one or more denticles posteroventrally on pleuron; fourth pleuron armed with sharp posteroventral tooth and additional denticles or teeth on posterolateral and/or ventral margins; fifth pleuron with posteroventral tooth and additional teeth on posterolateral margin. Telson (Figure 15E) with dorsolateral spines in linear row; posterior margin distinctly bilobed, with row of spines (Figure 15F).

Eyes fused, though distinct median notch present; anterior surface rounded, unarmed (Figure 15C).

Antennular stylocerite slender, narrowly separated from first peduncular segment (Figure 15C). Antenna not forming operculate structure; antennal scale with sharp distolateral tooth clearly separated from lamella; no transverse suture extending mesially from base of distolateral tooth (Figure 15C).

First maxilliped without rudimentary bud of exopod. Third maxilliped with two or more slender spines at ventrodistal margin of antepenultimate segment (Figure 15G).

First pereopod with short grooming setae on flexor surface of palm; carpus with well-developed grooming apparatus consisting of patch of short setae and one or two spinules proximal to setal patch. Second pereopod (Figure 15H) with one spine on ischium. Third to fifth pereopods increasing in length posteriorly; dactyli each with seven or eight accessory spinules arranged in two longitudinal rows on flexor surface (Figure 15I); meri of third and fourth pereopods each with one to three spines on lateral faces, that of fifth pereopod unarmed; ischia of third and fourth pereopods each with one or two spines, that of fifth pereopod unarmed. No strap-like epipods on third maxilliped or first to fourth pereopods.

Endopod of male first pleopod not bilobed distally, with three stiff setae distomesially; lateral margin with six or seven stiff setae in distal 0.3. Appendix interna of fourth pleopods without terminal cluster of coupling hooks. Uropodal exopod with one spine just mesial to base of posterolateral tooth; protopod sharply pointed posterolaterally.

Lau Basin (Zelnio and Hourdez 2009; this study), 1740–2700 m depths; North Fiji Basin, 2750 m depth (new record); and Vanuatu, Nifonea vent field, 1871 m depth (new record).

The present specimens are consistent with the original description of Alvinocaris komaii in every diagnostic aspect.

Molecular phylogenetic analysis based on 600 bp of the mitochondrial COI nucleotide by Zelnio and Hourdez (2009) suggested that A. komaii was clustered with the Opaepele / Chorocaris / Rimicaris clade, although the bootstrap support was very low (39.7%). As described previously by Zelnio and Hourdez (2009), A. komaii differs from other species of Alvinocaris in the accessory spinules on the dactyli of the third to fifth pereopods arranged in two or more rows and the unarmed anterior face of each eye. These characters, and the molecular analysis presented herein support the closer relationship of the species to a group including Alvinocaridinides, Chorocaris, Opaepele, Shinkaicaris and Rimicaris. Furthermore, A. komaii has two unique characters within the family, namely, the distinctly bilobed posterior margin of the telson and the multiple spines on the ventrodistal margin of the antepenultimate segment of the third maxilliped. Future study may potentially warrant the establishment of a separate genus for A. komaii.

The ML tree inferred from partial COI sequences (460 bp) for 18 identified species (including the two new species referred to Chorocaris) and two unidentified species of the Alvinocarididae is shown in Figure 16. At present, COI sequences are not

available for the following 13 formally described species: Alvinocaridinides formosa Komai and Chan, 2010, Alvinocaris alexander Ahyong, 2009, Alvinocaris brevitelsonis Kikuchi and Hashimoto, 2000, Alvinocaris methanophila Komai, Shank and Van Dover, 2005, Alvinocaris niwa Webber, 2004, Alvinocaris williamsi Shank and Martin, 2003, Chorocaris paulexa, Chorocaris susannae, Manuscaris acuminatus gen. et sp. nov., Mirocaris indica Komai et al. (2006), Nautilocaris saintlaurentae Komai and Segonzac, 2004, Rimicaris kairei Watabe and Hashimoto, 2002, and Shinkaicaris luerokolos (Kikuchi and Hashimoto, 2000).

The two new species of Chorocaris are clustered in a clade consisting of C. chacei, C. vandoverae, Opepele loihi, Rimicaris exoculata and Rimicaris hybisae with relatively high bootstrap support (88%, 93% and 100% in ML, MP and NJ, respectively) (Figure 16). The relationship among these species could not be fully resolved, because some inner branches have weak bootstrap support (less than 70%; e.g. the position of C. parva sp. nov., C. vandoverae and C. variabilis sp. nov.). The monophyly of Chorocaris is not supported, with the two Rimicaris species and O. loihi subordinated within Chorocaris.

Interspecific divergence among these seven species is summarized in Table 1. The minimum divergence is seen between C. variabilis sp. nov. and C. parva sp. nov. (5.5– 6.7%), whereas the maximum divergence is seen between C. variabilis sp. nov. and O. loihi (11.0–11.5%). Previous studies on decapod crustaceans [e.g. Jones and Macpherson 2007 (Anomura: Munidopsidae: Munidopsis); Cabezas et al. 2009 (Anomura: Munididae: Munida and allied genera); Tsoi et al. 2011 (Achelata: Palinuridae: Linuparus); Chang et al. 2014 (Astacidea: Nephropidae: Thaumastocheles)] have shown that COI divergence of more than 10% is indicative of species level differentiation, although lower divergence (> 4.0%) could also be of specific significance [(e.g. Davie et al. 2010 (Brachyura: Micytlidae: Mictylis); Yang et al. 2010 (Caridea: Pandalidae: Heterocarpus)]. Together with the morphological evidence, we consider that full species status is warranted for the two new taxa described in this study.

Four specimens of C. variabilis sp. nov. (three from the Manus Basin and one from the North Fiji Basin) are clustered with well-supported bootstrap value (93%, 96% and 100% in ML, MP and NJ, respectively). The intraspecific divergence in the four specimens is 0.3–1.8 %, and there is little doubt that they belong to the same species.