Shinkaicaris, Komai & Segonzac, 2005

Komai, Tomoyuki & Segonzac, Michel, 2005, A revision of the genus AlIJinocaris Williams and Chace (Crustacea: Decapoda: Caridea: Alvinocarididae), with descriptions of a new genus and a new species of AlIJinocaris, Journal of Natural History 39 (15), pp. 1111-1175 : 1164-1169

Shinkaicaris gen. nov.

Type species

Alυinocaris leurokolos Kikuchi and Hashimoto, 2000 . Original designation by monotypy.

Diagnosis

Rostrum well developed, compressed laterally, always with dorsal teeth extending to anterior part of carapace. Carapace not extremely inflated, with moderately large antennal and large pterygostomian tooth; antennal tooth distinctly buttressed, suborbital margin of carapace just mesial to antennal tooth forming conspicuous lobe; post-antennal groove shallow, but distinct. Fourth and fifth abdominal pleura dentate posterolaterally. Telson with dorsolateral spines arranged in sinuous rows; posterior margin convex, with two pairs of lateral spines and row of numerous plumose setae. Eyes lacking corneal facets, but with diffused pigmentation inside, broadly fused mesially; anterior surface without tubercle. Antennal scale broadly oval, not locked with antennule. Third maxilliped to fourth pereopods without strap-like epipods. Ischium of second pereopod lacking ventrolateral spine. Dactyli of third to fifth pereopods somewhat compressed laterally, each with three or four rows of accessory spines on ventral margin; meri and ischia of third to fifth pereopods unarmed. Branchial formula identical to that of Alυinocaris. Second to fourth pleopods each with slender, simple appendix interna in both sexes; fifth pleopod with well-developed appendix interna bearing terminal cluster of cincinnuli.

Remarks

Shinkaicaris leurokolos is superficially similar to species of Alυinocaris in the laterally compressed, dorsally dentate rostrum, a plesiomorphic feature within the Alvinocarididae . Presumably apomorphic characters in S. leurokolos , such as the broadly fused eyes, sinuous rows of the dorsolateral spines on the telson, the possession of three or more rows of accessory spines on the ventral surfaces of the dactyli of the third to fifth pereopods, and the unarmed ischium of the second to fifth pereopods, are shared by Chorocaris , Opaepele , and Rimicaris . Although Kikuchi and Hashimoto (2000) reported the presence of a spiniform tubercle on the anterior surface of the eye in S. leurokolos , our re-examination of the type series has shown that there is no spiniform tubercle on the eye. The distinctly buttressed antennal tooth and the presence of a small rounded lobe on the suborbital margin of the carapace are unique for S. leurokolos among alvinocaridids. Shinkaicaris is further distinguished from the fifth alvinocaridid genus Mirocaris by having dorsolateral spines on the telson arranged in sinuous rows, the possession of more than two rows of accessory spines on the ventral surfaces of the third to fifth pereopods and the absence of pereopodal epipods. The presence of a strong, sharp pterygostomian tooth also differentiates Shinkaicaris from Chorocaris , Mirocaris , and Rimicaris .

Shinkaicaris leurokolos ( Kikuchi and Hashimoto, 2000) , comb. nov. ( Figures 27 , 28 )

Alυinocaris breυitelsonis Kikuchi and Hashimoto 2000, p 141 (part), Figure 3i .

Alυinocaris leurokolos Kikuchi and Hashimoto 2000, p 141 , Figures 4–7 [type locality: Depression C, Minami-Ensei Knoll, Mid-Okinawa Trough, 28 ° 23.359N, 127 ° 38.389E, 705 m].

Material examined

Okinawa Trough. DS Shinkai 2000 : dive 549, Depression C, Minami-Ensei Knoll , 28 ° 23.359N, 127 ° 38.389E, 705 m, 3 June 1991, suction sampler, coll. J. Hashimoto, one ovigerous female CL 12.5 mm (holotype; NSMT-Cr 12457); two males CL 10.5, 11.5 mm, two females CL 9.2, 9.9 mm (paratypes; NSMT-Cr 12459) .

Description

Integument of body thin, but not membranous, surface shining.

Rostrum ( Figure 27A, B ) compressed laterally, reaching distal margin of first segment to midlength of second segment of antennular peduncle; dorsal margin armed with 7–10 teeth slightly diminishing in size anteriorly, including six to nine on rostrum proper and one to three on carapace, posteriormost tooth arising from level of posterior margin of orbit to 0.08 of carapace length; lateral carina sharp, broadened proximally and confluent with orbital margin; ventral surface bluntly carinate medially, unarmed. Carapace ( Figure 27A, B ) somewhat compressed laterally; postrostral median ridge relatively low, rather blunt, extending to 0.40 length of carapace; antennal tooth sharp, distinctly buttressed, margin inferior to antennal tooth forming small rounded lobe ( Figure 27C ); pterygostomian tooth much larger than antennal tooth, strongly produced anteriorly; lateral surface of carapace with shallow post-antennal groove originating inferior to base of antennal tooth, passing obliquely ventrad and extending to hepatic region. Strong median sternal spine between coxae of fifth pereopods.

Abdomen (cf. Figure 27D ) smooth dorsally; pleural margin of anterior two somites broadly rounded, that of third somite broadly rounded or with one small posteroventral tooth; pleuron of fourth somite with acute posterolateral tooth and occasionally with additional one to three acute teeth on posterior margin; pleuron of fifth somite with two to four posterior teeth including posteroventral tooth. Sixth somite 1.20–1.30 times as long as proximal height, with sharp posterolateral process and posteroventral tooth. Telson ( Figure 27E ) elongate subrectangular, length 2.50–2.90 times anterior width, 2.90–3.20 times posterior width, with five to seven dorsolateral spines arranged in a sinuous row; posterior margin convex, with two pairs of lateral spines (mesial pair longer than lateral) and 22–24 long plumose setae ( Figure 27F ).

Eyes ( Figure 27 A–C) on basally separated, movable stalks broadly fused mesially; division of corneal region and stalk unclear; corneal region, unfaceted, with irregular, scattered pigment-like masses within stalk; anteromedial face flat, sloping to anterolateral face, without spiniform tubercle on anterior surface.

Antennular peduncle ( Figure 27A, B ) moderately stout. First segment with conspicuous fossa on dorsal surface subproximally, and with conspicuous distolateral tooth; stylocerite slender, reaching midlength to distal margin of second segment, slightly depressed dorsoventrally, sharp, separated from first segment by narrow, deep incision and succeeding deep groove; dorsal surface of stylocerite with distinct rounded tubercle subproximally and transverse row of setae somewhat distal to subproximal tubercle. Second segment 1.30–1.50 times as long as wide, with distomesial tooth. Third segment short. Dorsolateral flagellum longer than carapace, thickened aesthetasc-bearing portion in basal 0.40–0.50, ventromesial flagellum somewhat longer.

Antenna ( Figure 27A, B ) with stout basicerite bearing ventrolateral distal spine and ventrodistal spine. Antennal scale ( Figure 28A ) 0.48–0.52 times as long as carapace, 1.70– 2.00 times as long as wide; lateral margin straight or slightly convex, strongly converging against dorsal median ridge; distolateral tooth broad, directed forward, falling short of broadly rounded distal margin of blade, mesial margin slightly curved or straight. Carpocerite moderately stout. Antennal flagellum longer than body.

Mouthparts similar to those of Alυinocaris (illustrated by Kikuchi and Hashimoto 2000). Third maxilliped ( Figure 28B, C ) slender, composed of four segments, reaching beyond distal end of antennal scale by half length of ultimate segment; distal two segments slightly arched in lateral view; ultimate segment trigonal in cross-section, tapered distally, bearing terminal cluster of five to seven small spines, row of sparse long spiniform setae on dorsomesial, dorsolateral and ventral margins, and transverse tracts of dense setae along mesial face; carpus (penultimate segment) shorter than ultimate segment, also with transverse tracts of setae on mesial face; antepenultimate (merus–ischium–basis fused segment) subequal to distal two segments combined, somewhat sinuously curved in dorsal view, distal half weakly compressed laterally and proximal half somewhat flattened dorsoventrally, with slender spine at distolateral ventral corner, margins with short to long setae; mesial face with some short oblique rows of spiniform setae distal to midlength of segment; tufts of long setae at proximomesial portion of antepenultimate segment; coxa with epipod rather abruptly tapering distally ( Figure 27D ); exopod absent.

First pereopod ( Figure 28E ) falling short of tip of third maxilliped, moderately robust, not strongly polymorphic. Fingers curved downward and inward; dactylus more than three times longer than palm; outer surface of both fingers convex, inner concavity with opposed edges uniformly offset, closing without gape, each armed with fine row of almost uniform, erect, corneous teeth so closely set as to be contiguous, tip of each finger slightly spooned; submarginal row of tufts of short sensory setae on inner surface along cutting edges. Palm extremely short, inflated ( Figure 28F ). Carpus cupped distally to receive palm; dorsodistal margin not produced; ventral surface flared into weak lateral ridge terminating in small tooth and smaller mesial ridge ending bluntly, surface between ridges with thick grooming setae and one or two movable spines; mesial face with shallow depression. Merus and ischium obliquely articulated in lateral view; merus not inflated ventrally, without small subdistal tooth on ventrolateral margin; ischium always unarmed.

Second pereopod subequal in length to, but more slender than first pereopod, not reaching distal margin of antennal scale. Fingers subequal in length to palm, each terminating in small, corneous unguis crossing each other when closed, cutting edges without gape, each pectinate with single row of minute teeth directed obliquely distally and increasing slightly in size. Carpus slightly longer than chela. Merus and ischium obliquely articulated in lateral view; ischium unarmed.

Third to fifth pereopods (cf. Figure 28G ) moderately slender, generally similar in length and structure, third reaching beyond distal margin of antennal scale by 0.30–0.40 length of propodus. Propodus–carpus combined shorter than merus–ischium combined in third, subequal in fourth, and longer than in fifth. Dactyli (cf. Figure 28H, I ) short, 0.18–0.22 times as long as propodi, terminating in strong unguis, armed with 13–16 accessory spines arranged in three or four rows on flexor surface; accessory spines grading from small proximally to longest and strongest distally. Propodi of third and fourth pereopods with slender spinules arranged in two rows on ventral surface; propodus of fifth pereopod with numerous spiniform setulose setae arranged in three or four rows on distal half of ventral surface. Carpi distinctly shorter than propodi. Meri and ischia unarmed.

First to fourth pereopods each without pre-coxal spine.

Pleopods well developed. First pleopod with endopod 0.50–0.60 length of exopod, sexually dimorphic; in males, distal part abruptly narrowed, bearing four to six curved spiniform setae; in females, distal part gradually tapered, with fringe of plumose setae similar to those fringing remaining margins. Second to fifth pleopods with endopods slightly shorter than exopods; appendices internae on second to fourth pleopods not greatly reduced in size, but slender, simple; appendix interna on fifth pleopod more stout than others, with distomesial cluster of cincinnuli. Appendix masculina robust, slightly shorter than appendix interna, with several (up to eight) terminal and subterminal spines.

Uropod ( Figure 27E ) with rami subequal in length, exopod with small movable spine mesial to smaller distolateral tooth and sinuous diaeresis (not depicted on Figure 27E ).

Distribution and habitat

Known only from Minami-Ensei Knoll, Mid-Okinawa Trough, at a depth of 705 m. This species occurs in a thermally influenced area.

Variation

Variation in the rostral shape and armature was fully illustrated by Kikuchi and Hashimoto (2000, Figure 7 a–j). It is noteworthy that this species does not show strong polymorphism in the morphology of the first pereopod.

Figures

Figure 3. Alυinocaris muricola Williams, 1988. Left thoracic appendages. (A) Third maxilliped, lateral; (B) coxa and antepenultimate segment of third maxilliped, dorsal; (C) first pereopod, lateral; (D) carpus of first pereopod, mesial; (E) second pereopod, lateral; (F) chela of second pereopod, dorsal; (G) third pereopod, lateral; (H) dactylus of third pereopod, lateral; (I) fourth pereopod, lateral; (J) fifth pereopod, lateral; (K) dactylus of fifth pereopod, lateral. Female from Régab site, west equatorial African margin (CL 16.8 mm; MNHN-Na 14277).

Figure 4. Alυinocaris lusca Williams and Chace, 1982. (A) Carapace and cephalic appendages, lateral (rostrum broken off); (B) anterior part of carapace and cephalic appendages, dorsal; (C) same, lateral; (D) carapace, dorsal (rostrum broken off); (E) third to sixth abdominal somites, lateral. (A, B, D, E) Paratype female from Rose Garden area, Galapagos Rift (CL 13.5 mm; USNM 184537); (C) paratype female (CL 8.6 mm; same lot).

Figure 5. Alυinocaris lusca Williams and Chace, 1982. (A) Telson and right uropod, dorsal; (B, C) posterior part of telson, dorsal; (D) right antennal scale, dorsal (marginal setae omitted); (E) first pereopod, lateral; (F) chela of first pereopod, outer; (G) left third pereopod, lateral; (H) dactylus and distal part of propodus of left third pereopod, lateral. (A, B, D–H) Paratype female from Rose Garden area, Galapagos Rift (CL 13.5 mm; USNM 184537); (C) paratype (CL 8.6 mm; same lot).

Figure 6. Alυinocaris markensis Williams, 1988. (A) Carapace and cephalic appendages, lateral; (B) anterior part of carapace and cephalic appendages, dorsal; (C) carapace, dorsal; (D) third to sixth abdominal somite, lateral; (E) telson and right uropod, dorsal; (F) posterior part of telson, dorsal. Female from site Les Ruches, Snake Pit, Mid-Atlantic Ridge (CL 16.7 mm; MNHN-Na 14282).

Figure 7. Alυinocaris markensis Williams, 1988. (A) Left antennal scale, dorsal; (B) left first pereopod, lateral; (C) chela of left first pereopod, outer; (D) left third pereopod, lateral; (E) dactylus and distal part of propodus of left third pereopod, lateral. Female from site Les Ruches, Snake Pit, Mid-Atlantic Ridge (CL 16.7 mm; MNHN- Na 14282).

Figure 27. Shinkaicaris leurokolos (Kikuchi and Hashimoto, 2000), comb. nov. (A) Carapace and cephalic appendages, lateral; (B) anterior part of carapace and cephalic appendages, dorsal; (C) eye, left orbit and antennal tooth, dorsal; (D) third to sixth abdominal somites, lateral; (E) telson and right uropod, dorsal (marginal setae on uropod omitted); (F) posterior margin of telson, dorsal. Paratype female from Minami-Ensei Knoll, Mid-Okinawa Trough (CL 11.6 mm; NSMT-Cr 12459).

Figure 28. Shinkaicaris leurokolos (Kikuchi and Hashimoto, 2000), comb. nov. (A) Left antennal scale, dorsal (marginal setae omitted); (B) left third maxilliped, lateral; (C) antepenultimate segment (merus–ischium–basis fused segment) of left third maxilliped, mesial; (D) coxa, epipod and basal part of antepenultimate segment of left third maxilliped, dorsal; (E) left first pereopod, lateral; (F) chela of left first pereopod, outer; (G) left third pereopod, lateral; (H) dactylus and distal part of propodus of left third pereopod, lateral; (I) same, ventral. Holotype female from Minami-Ensei Knoll, Mid-Okinawa Trough (CL 11.6 mm; NSMT-Cr 12457).