Manuscaris acuminatus, Komai & Tsuchida, 2015

Komai, Tomoyuki & Tsuchida, Shinji, 2015, New records of Alvinocarididae (Crustacea: Decapoda: Caridea) from the southwestern Pacific hydrothermal vents, with descriptions of one new genus and three new species, Journal of Natural History (J. Nat. Hist.) 49, pp. 1-36 : 23-29

Manuscaris acuminatus sp. nov.

( Figures 11–14 )

Type material

Holotype. Wave Mercury 2007 Campaign, dive 35, South Su , Manus Basin , 3°08.09 ʹ N, 152°10.5 ʹ E, 1310 m, 15 April 2007, male (cl 8.4 mm), CBM-ZC 11,955.

Description of holotype

Body integument fairly thin, almost glabrous on surface.

Rostrum ( Figure 12A, B) narrowly triangular in dorsal view, slightly overreaching distal margin of first segment of antennular peduncle, about 0.4 times as long as carapace; dorsal margin carinate, with 11 unequal teeth, posteriormost and distal two teeth distinctly smaller than other teeth, posteriormost tooth located slightly posterior to orbital margin; sparse short setae on proximal five teeth; ventral surface nearly flat (non-carinate), with minute denticle subterminally; ventrolateral carina sharply defined, merging into orbital margin. Carapace ( Figures 11 , 12C) with low, blunt postrostral carina not extending to midlength, so dorsal margin in lateral view nearly straight; antennal tooth slender, acuminate, with small blunt lobe ventromesial to its base; pterygostomial tooth strong, reaching slightly beyond tip of antennal tooth; anterior part of branchial region not inflated.

Pleon as figured ( Figure 11 ). Third pleuron with one small posteroventral tooth; fourth pleuron with one rather strong posteroventral tooth and one much smaller additional tooth anterior to it on ventral margin; fifth pleuron with strong posteroventral tooth and one additional conspicuous tooth on posterolateral margin. Sixth pleomere 1.6 times as long as fifth pleomere and 1.2 times longer than high, with strong, acute posteroventral tooth; posterolateral process terminating in sharp tooth. Telson ( Figure 12E) 3.1 times longer than anterior width, armed with seven dorsolateral spines arranged in linear row on either side and two pairs of posterolateral spines; posterior margin with 14 long plumose setae ( Figure 12F).

Eyes ( Figure 12B) broadly fused, but with shallow median groove, closely approximated to ventral face of rostrum; each anterior surface nearly flat, unarmed.

Antennular peduncle ( Figure 12A, B) reaching distal margin of antennal scale. First segment with forwardly directed, spiniform proximolateral tubercle; distolateral tooth long, slender, reaching beyond midlength of second segment, distomesial margin with small tooth; stylocerite slender, slightly diverging, reaching nearly to distal margin of second segment. Second segment 1.6 times as long as wide, with small distomesial tooth.

Antenna ( Figure 12A, B) with basicerite bearing a slender ventrolateral tooth and a sharp ventral tooth. Carpocerite moderately stout, slightly overreaching midlength of antennal scale. Antennal scale about 0.5 times as long as carapace and 2.2 times longer than wide; lateral margin nearly straight; distolateral tooth slender, clearly separated from distal lamella by rather narrow, deep notch, tooth reaching distal margin of lamella; no suture mesial to base of distolateral tooth; dorsal carina distinct, slightly diverging from lateral margin; distal lamella rounded.

Mandible ( Figure 13A ) with terminally blunt molar process; incisor process with six triangular teeth mesially. Maxillule ( Figure 13B ) endopod slightly bilobed, distomesial lobe with one apical plumose seta, distolateral lobe with two minute submarginal setae. Maxilla ( Figure 13C ) with scaphognathite moderately broad, with some short facial setae restricted to mesial part. First maxilliped ( Figure 13D ) with rudimentary bud of flagellum on mesial margin of broad exopod; endopod ( Figure 13D , inset) short, bi-articulated. Second maxilliped ( Figure 13E ) with relatively stout endopod; epipod subsemicircular, bearing slender, rod-like, non-lamellate podobranch.

Third maxilliped ( Figure 14A) typical of alvinocaridid, slightly overreaching distal margin of antennal scale. Distal two segments combined gently arcuate, ultimate segment tapering distally, trigonal in cross-section, about 1.2 times as long as penultimate segment (= carpus). Antepenultimate segment with slender ventrolateral distal spine and prominent tuft of setae on dorsomesial proximal part. Epipod widened distally, slightly bilobed, lacking strap-like process ( Figure 14B).

First pereopod ( Figure 14C) slightly falling short of distal margin of antennal scale; dactylus 5.5 times longer than palm; chela ( Figure 14D) slender, 2.8 times longer than wide; carpus ( Figure 14E) relatively slender, with blunt ventrodistal tooth; mesial surface ventrally with grooming apparatus consisting of patch of short stiff setae and one small spine proximal to patch of setae ( Figure 14E). Second pereopod ( Figure 14F) not reaching distal margin of antennal scale; chela 0.8 times as long as carpus; dactylus subequal in length to palm ( Figure 14G); ischium with one spine laterally. Third pereopod ( Figure 14H) overreaching antennal scale by full length of dactylus and propodus combined; dactylus ( Figure 14I, J) 0.2 times as long as propodus, terminating in strong, clearly demarcated unguis, bearing four pairs of accessory spinules on flexor surface; propodus ( Figure 14K) with two rows of slender spinules on flexor surface in distal half; carpus 0.9 times as long as propodus; merus 6.6 times longer than wide; ischium with two spines ventrolaterally. Fourth pereopod missing. Fifth pereopod ( Figure 14L) longer than third pereopod, overreaching antennal scale by about 0.8 length of propodus; dactylus ( Figure 14M, N) with 12 accessory spinules arranged in two or three rows on flexor surface ( Figure 14N); propodus with three or four irregular rows of slender spines or spiniform setae on flexor surface ( Figure 14N); carpus 1.6 times as long as propodus; merus about 7.3 times longer than wide; ischium unarmed.

Endopod of male first pleopod ( Figure 12H) with inner lobe produced, far exceeding outer lobe, bearing cluster of five spiniform setae distally; outer lobe broadly rounded, with five spiniform setae; lateral margin slightly convex, with five stout plumose setae; mesial margin faintly sinuous, with 10 stout plumose setae. Appendices internae of second to fifth pleopods normally developed, with terminal cluster of coupling hooks, while that on fifth pleopod lacking coupling hooks. Appendix masculina on second pleopod ( Figure 12I) tapering distally, slightly longer than appendix interna, armed with about seven spiniform setae distally. Uropodal rami ( Figure 12E) both overreaching posterior margin of telson; exopod with one slender spine just mesial to sharp posterolateral tooth ( Figure 12K).

Coloration in life

Not known.

Distribution

Known only from the type locality, South Su hydrothermal vent field, Manus Basin , 1310 m depth .

Etymology

From the Latin, acuminatus (= sharp), in reference to the sharp stylocerite and proximolateral tubercle on the first segment of the antennular peduncle.

Figures

Figure 11. Manuscaris acuminatus gen. et sp. nov., holotype, male (carapace length 8.4 mm), CBM-ZC 11955, entire animal in lateral view. Scale bar: 2 mm.

Figure 13. Manuscaris acuminatus gen. et. sp. nov., holotype, male (carapace length 8.4 mm), CBM-ZC 11955. Left mouthparts. (A) Mandible, inner view; (B) maxillule, outer view (coxal endite missing); (C) maxilla, outer view; (D) first maxilliped, outer view; inset, endopod, inner view; (E) left second maxilliped, outer view. Scale bars: 1 mm for C–E; 0.5 m for A, B.