Alvinocaridinides semidentatus, Komai, Tomoyuki, Menot, Lenaick & Segonzac, Michel, 2016

Komai, Tomoyuki, Menot, Lenaick & Segonzac, Michel, 2016, New records of caridean shrimp (Crustacea: Decapoda) from hydrothermally influenced fields off Futuna Island, Southwest Pacific, with description of a new species assigned to the genus Alvinocaridinides Komai & Chan, 2010 (Alvinocarididae), Zootaxa 4098 (2), pp. 298-310 : 300-305

publication ID	https://doi.org/ 10.11646/zootaxa.4098.2.5
publication LSID	lsid:zoobank.org:pub:3C6101C4-EA1B-469A-BDB4-CD80B222A05C
DOI	https://doi.org/10.5281/zenodo.4608289
persistent identifier	https://treatment.plazi.org/id/03CFBC4C-4A51-515B-6FC9-9009FAEDD0AD
treatment provided by	Plazi
scientific name	Alvinocaridinides semidentatus
status	sp. nov.

Treatment

Alvinocaridinides semidentatus View in CoL n. sp.

Figs 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5

Material examined. Holotype: DS “Nautile”, dive 1778, Kulo Lasi, Futuna, 14°54.9653’S, 177°14.607’W, 1477 m, 13 September 2010, slurp gun, bottle 4, male (cl 8.3 mm), MNHN-IU-2013-19402.

Description. Holotype male. Body ( Fig. 1 View FIGURE 1 ) integument almost glabrous, but with sparse very short setae on dorsal margin of rostrum to postrostral region of carapace.

Rostrum ( Fig. 2 View FIGURE 2 A–C) dorsoventrally flattened, directed forward, triangular in dorsal view, reaching midlength of first segment of antennular peduncle, terminating in acute tip; dorsal surface bluntly carinate medially, armed with 4 small but conspicuous, sharp teeth only in distal half, and with short setae along midline; ventral surface slightly convex, unarmed; lateral margin merging into orbital margin. Carapace ( Figs 1 View FIGURE 1 , 2 View FIGURE 2 A, B) with dorsum nearly straight in lateral view; antennal tooth acute, directed anteriorly; pterygostomial angle terminating into sharp tooth directed forward and slightly exceeding beyond antennal tooth.

Pleon ( Fig. 1 View FIGURE 1 ) dorsally rounded. First to third pleura broadly rounded, unarmed on margins; fourth pleuron with tiny posteroventral tooth, otherwise unarmed; fifth pleuron with moderately strong posteroventral tooth and 1 additional tooth on posterior margin. Sixth pleomere 1.7 times as long as fifth pleomere and 1.5 times as long as high, with tiny posteroventral tooth, posterolateral process terminating in sharp tooth. Telson ( Fig. 2 View FIGURE 2 D, E) falling well short of posterior margins of uropods, 2.7 times as long as greatest width at midlength, armed with 6 (left) or 7 (right) dorsolateral spines arranged in sinuous row (second and third spines located more mesially than first or other spines); lateral margins faintly convex; posterior margin well produced, strongly convex, with row of long plumose setae flanked by 2 pairs of spines at posterolateral angles (mesial spine much longer than lateral spine).

Eyes ( Fig. 2 View FIGURE 2 A, B) broadly fused with faint median notch, lacking setae on anterior surface, clearly separated from ventral surface of rostrum; no spinule or tubercle on each anterior surface.

Antennular peduncle ( Fig. 2 View FIGURE 2 A, B) stout, falling slightly short of distal margin of antennal scale. First segment with moderately large distolateral tooth and small distomesial tooth and bluntly pointed proximolateral tubercle; stylocerite slender, nearly straight, reaching midlength of second segment. Second segment about 1.2 times as long as wide, with distomesial tooth larger than corresponding tooth on first segment.

Antennal peduncle ( Fig. 2 View FIGURE 2 A, B, F) with stout basicerite bearing ventrolateral distal tooth extending as far as dorsolateral distal projection, ventral surface without conspicuous tooth or projection. Fifth segment (= carpocerite) slightly overreaching midlength of antennal scale. Antennal scale suboval, about half as long as carapace, 2.0 times as long as wide; distolateral tooth acuminate, clearly separated from lamella, not reaching distal margin of lamella.

Mouthparts typical of family (for detailed description, see Komai and Segonzac 2003, 2005; Komai et al. 2007), as figured ( Figure 3 View FIGURE 3 A–H). Endopod of maxillule with 1 apical plumose seta at inner distal angle and 1 terminal and 1 shorter subterminal setae on outer lobule ( Fig. 3 View FIGURE 3 C). Maxilla ( Figure 3 View FIGURE 3 D) with broad scaphognathite, devoid of bacteriophore setae on ventral surfaces; posterior lobe subtriangular, tapering to rounded apex. Endopod of first maxilliped somewhat compressed, uniarticulate ( Fig. 3 View FIGURE 3 F); exopod with rudimentary bud of flagellum ( Fig. View FIGURE 3

3F). Second maxilliped ( Fig. 3 View FIGURE 3 G) with fairly stout endopod; epipod roundly triangular, with simple, slender podobranch with tip exceeding margin of epipod ( Fig. 3 View FIGURE 3 H).

Third maxilliped ( Figure 4 View FIGURE 4 A) overreaching distal margin of antennal scale by 0.3 length of ultimate segment, moderately slender. Ultimate segment tapering to subtruncate tip bearing 2 unequal spines, trigonal in cross section, with row of stiff setae on lateral ridge. Ultimate and penultimate segments gently arcuate. Antepenultimate segment sinuous, with slender spine at ventrolateral distal angle and prominent tuft of long setae at proximomesial portion on dorsal surface. Coxa with epipod subtruncate terminally ( Fig. 5 View FIGURE 5 A), without strap-like projection.

First pereopod ( Fig. 4 View FIGURE 4 B) fairly stout, overreaching distal margin of antennal scale by length of fingers. Chela ( Fig. 5 View FIGURE 5 B) distinctly longer than carpus; palm squarish, subequal in length to carpus; fingers strongly curved inward, inner side forming spoon-like excavation, fixed finger somewhat deflexed; cutting edges of fingers each pectinated with fine row of minute corneous teeth. Carpus cup-shaped; ventral margin with prominent, subtriangular tooth subdistally; mesial face shallowly excavated medially, bearing grooming apparatus consisting of patch of stiff setae and 1 proximal spinule ( Fig. 5 View FIGURE 5 C). Merus somewhat inflated on ventral surface medially; articulation to ischium strongly oblique.

Second pereopod ( Fig. 4 View FIGURE 4 C) reaching distal margin of antennal scale. Chela ( Fig. 5 View FIGURE 5 D) 1.3 times as long as carpus; fingers each terminating in distally curved, crossing tip, cutting edge pectinated with row of minute spinules; dactylus about 1.1 times as long as palm, slightly widened medially. Carpus slightly widened distally. Ischium unarmed.

Third pereopod ( Fig. 4 View FIGURE 4 D) overreaching antennal scale by full length of propodus; dactylus only slightly compressed laterally, 0.2 times as long as propodus, terminating in strong, slightly curved unguis, broad flexor surface with 7 spinules arranged in 2 rows ( Fig. 5 View FIGURE 5 E, G); propodus with 1 pair of distal spinules and 1 row of closely spaced minute spiniform setae on flexor surface extending to proximal 0.2 ( Fig. 5 View FIGURE 5 E, F), dorsal and mesial faces with scattered short setae; carpus 0.9 times as long as propodus; merus unarmed; ischium with 2 spines on lateral surface ventrally. Fourth pereopod ( Fig. 4 View FIGURE 4 E) similar to third pereopod, but slightly shorter; ischium with 1 spine. Fifth pereopod ( Fig. 4 View FIGURE 4 F) generally similar to third and fourth; propodus with spiniform setae arranged in 2 longitudinal rows, lateral row consisting of minute spinules extending to proximal 0.2 and more widely spaced toward proximal, mesial row consisting of widely spaced spinules restricted in distal 0.3; propodus and carpus combined distinctly longer than merus and ischium combined; ischium unarmed.

No epipods on first to fourth pereopods.

Endopod of male first pleopod ( Fig. 2 View FIGURE 2 G) with distomesial lobe prominent, tapering, with numerous long spiniform setae directed distally or mesially, distolateral lobe obsolete; mesial margin with row of plumose setae, lateral margin also with row of spiniform setae followed by row of plumose setae. Second pleopod with appendix masculina ( Fig. 2 View FIGURE 2 H) stout, tapering to blunt apex, bearing 6 spiniform setae distally and subdistally appendix interna short, slender. Third and fourth pleopods each with fairly reduced appendix interna lacking coupling hooks. Fifth pleopod with normally developed appendix interna bearing coupling hooks mesiodistally.

Uropod with protopod bearing terminally acute posterolateral process ( Fig. 1 View FIGURE 1 ); exopod with 2 subequal spines at posterolateral angle ( Fig. 2 View FIGURE 2 I).

Distribution. Known only from the type locality, Kulo Lasi site, off Futuna Islands, at a depth of 1477 m.

Remarks. The genus Alvinocaridinides was established by Komai & Chan (2010) to accommodate A. formosa Komai & Chan, 2010 . Vereshchaka et al. (2015) performed a phylogenetic analysis of Alvinocarididae using morphology and sequences of mitochondrial COI gene and clarified the generic level classification. As a result, they retained Alvinocaridinides as a valid genus, although the phylogenetic position of the taxon was not fully resolved. We assign our new species to Alvinocaridinides , one of the genera intermediate between the rather conservative Alvinocaris Williams & Chace, 1982 and the highly derived Rimicaris Williams & Rona, 1986 (cf. Vereshchaka et al. 2015) because of the following features: (1) rostrum dorsoventrally flattened, terminally acute, dentate dorsally but non-dentate ventrally; (2) rostral ridge not extending onto dorsum of carapace; (3) antennal and pterygostomial tooth acuminate, no suborbital lobe differentiated; (4) pleura of fourth and fifth pleomeres weakly dentate marginally; (5) telson with dorsolateral spines arranged in sinuous row; (6) dactyli of third to fifth pereopods less compressed, with accessory spinules on flexor surfaces arranged in two rows; (7) meri of third to fifth pereopods unarmed; (8) exopod of uropod with two posterolateral spines.

The new species exhibits unusual features for Alvinocarididae : (1) the dorsal margin of the rostrum is armed only on the distal half with small but conspicuous teeth; (2) the propodi of the third and fourth pereopods bear a single row of closely spaced minute spiniform setae on the flexor surface respectively. In species of Alvinocaris Williams & Chace, 1982 , Alvinocaridinides , Manuscaris Komai & Tsuchida, 2015 , Nautilocaris Komai & Segonzac, 2004 and Shinkaicaris Komai & Segonzac, 2005 , the dorsal margin of the rostrum is armed with teeth over the entire length ( Komai & Segonzac 2004, 2005; Webber 2004; Komai et al. 2005; Ahyong 2009; Zelnio & Hourdez 2009; Komai & Chan 2010; Yahagi et al. 2014; Komai & Tsuchida 2015) and while in species of Rimicaris Williams & Rona, 1986 , the dorsal surface of the rostrum is completely unarmed ( Komai & Segonzac 2003, 2008; Komai et al. 2006, 2007; Komai & Tsuchida 2015). In Keldishcaris vavilovi ( Lunina & Vereshchaka, 2010) and Opaepele loihi Williams & Dobbs, 1995 , the dorsal margin of the rostrum lacks conspicuous teeth, although there are sometimes minute notches suggesting the presence of rudimentary teeth ( Williams & Dobbs 1995; Lunina & Vereshchaka 2010). The propodi of the third and fourth pereopods are armed with two or more rows of moderately to widely separated spinules in all the other species of Alvinocarididae ( Komai & Segonzac 2003, 2004, 2005, 2008; Webber 2004; Komai et al. 2005, 2006, 2007; Zelnio & Hourdez 2009; Komai & Chan 2010; Lunina & Vereshchaka 2010; Nye et al. 2012; Yahagi et al. 2014; Komai & Tsuchida 2015; Komai, unpublished data).

Furthermore, A. semidentatus n. sp. differs from A. formosa in the following particulars: (1) the telson is not tapered posteriorly with faintly convex lateral margins in A. semidentatus n. sp., rather than regularly tapered posteriorly with straight lateral margins in A. formosa ; (2) the chela of the second pereopod is longer than the carpus in the new species, whereas the opposite in A. formosa ; (3) the dactyli of the third to fifth pereopods are less compressed in A. semidentatus n. sp. than in A. formosa ; and (4) the ischia of the third and fourth pereopods are armed with two and one spines respectively in A. semidentatus n. sp., rather than unarmed in A. formosa .

Komai & Chan (2010) argued that the unarmed ischia of the third and fourth pereopods are one of the possible apomorphic characters suggesting the relationship of Alvinocaridinides to Shinkaicaris , Opaepele and Rimicaris [now including Chorocaris synonymized by Vereshchaka et al. (2015)]. The present assignment of the new species to Alvinocaridinides might make Alvinocaridinides paraphyletic. Consequently, the generic assignment of the present new species should be considered provisional.

The holotype was sampled together with specimens of Rimicaris variabilis in a swarm of alvinovaridid shrimps lying on a pocket of hydrothermal sediments next to a small black smoker.

Etymology. The specific name is combined from the Latin semis (= half) and dentatus (= dentate), referring to the rostrum armed with teeth only on the distal half of the dorsal margin, an unusual feature in the family.