Nihonotrypaea thermophila Lin, Komai & Chan, 2007

Komai, Tomoyuki & Fujiwara, Yoshihiro, 2012, New records of callianassid ghost shrimp (Crustacea: Decapoda: Axiidea) from reducing environments in Kyushu, southwestern Japan, Zootaxa 3271, pp. 55-67 : 63-66

Nihonotrypaea thermophila Lin, Komai & Chan, 2007

( Figs 5–6 )

Nihonotrypaea thermophila Lin, Komai & Chan, 2007: 144 , figs 1–5A, B.

Material examined. 1 male (cl 9.6 mm), R/V Natsushima , NT05-12 cruise, ROV Hyper-Dolphin dive No. 454, Kinko Bay, Kagoshima Prefecture, 31°39.748’N, 130°48.064’E, 105 m, 28 July 2005, JAMSTEC No. 2050025167.

Comparative material. Paratypes: 1 male, 1 female, both damaged, TAIWAN 2001, stn CP 113, off Dasi fishing ground, off Kueishan Island, northeastern Taiwan, 24°50.809’N, 121°59.889’E, 281 m, 21 May 2001, CBM-ZC 8675.

Abbreviated description of Japanese specimen. Rostrum ( Fig. 5 B) broadly triangular with pointed apex. Carapace ( Fig. 5 A, B) with well delineated dorsal oval; cervical groove across 0.7 length of carapace; anterolateral projection small, triangular with blunt apex.

Sixth abdominal somite ( Fig. 5 C) about 1.2 times wider than long; lateral constriction at 0.7 length of somite. Telson ( Fig. 5 D) about 0.9 times as long as sixth somite, trapezoidal, approximately as long as wide, slightly narrowing posteriorly; posterior margin nearly straight, bearing small median spine; no movable spinules at rounded posterolateral angles.

Eyestalks ( Fig. 5 A, B) contiguous, gradually tapering distally to rounded distomesial margin; corneal spot small, much less than half of greatest width of eyestalk. Antennular peduncle ( Fig. 5 A, B) moderately long and slender, with third segment about 2.3 times longer than second segment. Antennal peduncle ( Fig. 5 A, B) moderately slender, overreaching antennular peduncle by 0.2 length of fifth segment.

Third maxilliped ( Fig. 6 A) with ischium-merus operculiform, about 1.6 times longer than wide, dorsal margin convex with peak at base of merus; merus about 0.8 times as long as ischium measured along ventral margin, distoventral margin produced in broadly rounded lobe.

Chelipeds greatly unequal and dissimilar. Major (right) cheliped ( Fig. 6 B) with ischium widened distally having strongly sinuous dorsal margin and serrated ventral margin. Merus with coarsely tuberculate dorsal and ventral margins, with prominent hook-like process proximoventrally. Carpus slightly longer than merus, subrectangular, with sharply carinate dorsal and ventral margins, proximal margin broadly convex. Palm subrectangular, approximately as long as wide, slightly narrowing distally; dorsomesial and ventromesial margins coarsely tuberculate. Fixed finger slightly curving, midline of mesial face with row of low tubercles ( Fig. 6 C). Dactylus slightly shorter than palm, hooked distally.

Minor (left) cheliped ( Fig. 6 D) much slenderer than major cheliped. Ischium curving, unarmed on dorsal and ventral margins. Merus with convex dorsal and ventral margins, latter with minute spine at midlength. Carpus elongate, 2.9 times longer than high, narrowing in proximal one-fifth. Chela about 0.9 times as long as carpus. Palm about 1.4 times longer than wide. Dactylus about 1.3 times longer than palm, crossing with fixed finger distally.

Third pereopod with carpus subtriangular with broadly convex distal margin; propodus with truncate distal margin, proximal heel rounded, not exceeding beyond ventral (flexor) margin of carpus ( Fig. 6 E).

Male first pleopod very small, uniramous, 2 segmented; second pleopod absent. Third to fifth pleopods broad; appendices internae stubby, only slightly projecting beyond mesial margin of endopod, bearing cluster of cincinnuli on distal two-thirds to three-fourths of mesial margin ( Fig. 5 E).

Uropodal endopod suboval in shape, not particularly narrowing distally, unarmed on dorsal surface or margins. Exopod slightly longer than endopod, broadly oval, terminal margin very broadly rounded; dorsal plate with distal row of setae distinctly separated from setal row of posterior margin.

Distribution. Previously known only from hydrothermally influenced field near Kueishan Island, Dashi fishing ground, off northeastern Taiwan, at depths of 128– 320 m. The present specimen represents the first record of this species from Japan and the first occurrence of non-hydrothermal environment.

Remarks. The present specimen agrees well with the type series of Nihonotrypaea thermophila in every diagnostic aspect, and is safely identified with that species. In the original description of N. thermophila, Lin et al. (2007) noted that the carpus of the minor cheliped is unarmed or armed with a ventral spine on the carpus of the minor cheliped, located at the proximal two-thirds. However, reexamination of the two paratypes (CBM-ZC 8675) has revealed that the position of the ventral spine is rather variable; in one of the two specimens, the spine is located at the midlength, as in the present Japanese specimen.

The type series of this species was collected from hydrothermally influenced field on Dashi fishing ground, off northeastern Taiwan. Our specimen was collected from hydrothermally influenced field in Kagoshima Bay, in which the siboglinid tube worm Lamellibrachia satsuma Miura, Tsukahara & Hashimoto, 1997 is abundant. This finding confirms that N. thermophila is associated with hydrothermalism.

Figures

FIGURE 5. Nihonotrypaea thermophila Lin, Komai & Chan, 2007, male (cl. 9.6 mm), JAMSTEC No. 2050025167. A, carapace and cephalic appendages, lateral view; B, anterior part of carapace and cephalic appendages, dorsal view; C, sixth abdominal somite, dorsal view; D, telson and left uropod, dorsal view (setae omitted); E, appendix interna of left third pleopod, ventral view. Scale bars: 2 mm for A – D; 0.5 mm for E.

FIGURE 6. Nihonotrypaea thermophila Lin, Komai & Chan, 2007, male (cl. 9.6 mm), JAMSTEC No. 2050025167. A, left third maxilliped, lateral view (setae omitted); B, right major cheliped, lateral view; C, tuberculate ridge on fixed finger of right major cheliped, mesial view; D, left minor cheliped, lateral view (proximal part of ischium omitted); E, distal 3 segments of left third pereopod, lateral view. Scale bars: 2 mm.