Guaplax, Naruse, Tohru, Ng, Peter K. L. & Guinot, Danièle, 2008

Naruse, Tohru, Ng, Peter K. L. & Guinot, Danièle, 2008, Two new genera and two new species of troglobitic false spider crabs (Crustacea: Decapoda: Brachyura: Hymenosomatidae) from Indonesia, with notes on Cancrocaeca Ng, 1991, Zootaxa 1739, pp. 21-40 : 31-32

Guaplax gen. nov.

Type species. Guaplax denticulata spec. nov. by present designation.

Diagnosis. Carapace subcircular, slightly wider than long, dorsal surface flat, surrounded by continuous rim, regions clearly separated by grooves; rostrum prominent, trilobed, lateral surface below posterolateral margin with 2 teeth. Anterior margin of cephalothorax produced anteriorly in lateral view; antennular fossae very shallow, medially separated by thin septum (proepistome); epistome with posterior margin gently produced.

Eye slightly visible from dorsal view, base of ocular peduncle fused to orbit, immovable, gradually narrowed distally; cornea without trace of black pigment. Antennule with swollen basal article, largely protruding from fossa. Antenna with thin basal article, base of basal article located at just below base of ocular peduncle, flagellum long. Third maxillipeds narrow, forming wide gape when closed; ischium with broad distal inner extension, merus with inner and outer margins divergent distally.

Male abdominal cavity relatively narrow; sternal button for abdominal locking mechanism undiscernible. Female with wide cephalothorax cavity; vulvae of thoracic sternite 6 without basal mount along imaginary line joining posterior margin of P2 coxae on medial fused plate of thoracic sternum. Chelipeds slender; chela with tapering fingers. Ambulatory legs slender; dactyli slightly incurving, ending in sharp spine, without subterminal tooth. Penis located anterior to middle of sternite 8.

Male abdomen-pleotelson 4-segmented, third to fifth segments fused; first segment with rounded lobe on disto-lateral angle, proximal part abruptly narrowed; fused segments narrowed in distal half; pleotelson distinctly narrower than half width of abdomen. G1 straight, tapering simply, dorsal side of inner margin lined with long, stiff setae; suture running from dorsal side of proximal part to outer margin of distal part; G2 with dilated base, proximal outer angle prominently produced, visible in dorsal view even from closed abdomen. Female abdomen with an undivided plate formed by fusion of second segment to pleotelson, second segment and pleotelson only demarcated by shallow groove on outer side; margin of inner surface of abdomen-pleotelson covered with thin membrane, forming pouch; second to fifth pleopods short, biramous, entirely enclosed inside pouch.

Etymology. Guaplax is derived from the Indonesian word gua, “cave”, and plax, “plate,” the last syllable of the closely related genus Neorhynchoplax . Gender feminine.

Remarks. As is the case of Sulaplax ensifer , Guaplax denticulata spec. nov. possesses male and female abdomens and G1 similar to those of Neorhynchoplax . However, G. denticulata shows significant generic differences from Sulaplax and Neorhynchoplax in the characters listed as follows.

Guaplax can be distinguished from Neorhynchoplax by the base of the basal antennal article being located below the base of the ocular peduncle ( Fig. 7 b) (located at just inner lower region with respect to the base of the ocular peduncle in Neorhynchoplax ), the presence of reduced eyes ( Fig. 7 a, b) (normal in Neorhynchoplax ), the distal outer angle of the first abdominal segment being lobe-like in both sexes ( Figs. 8 d, 9d) (entire in Neorhynchoplax ), and a lobe-like, dilated base of the G2 which remains exposed even when the second abdominal segment is completely appressed against the sterno-abdominal cavity ( Fig. 8 h) (G2 completely covered in Neorhynchoplax ).

The characters separating Guaplax from Sulaplax are the presence of a prominent and trilobed rostrum ( Fig. 7 a, b), the presence of teeth on the side walls of the carapace ( Fig. 7 a), epistome with a slightly produced posterior margin ( Fig. 7 b), short and wide distal inner projection of the ischium of the third maxilliped ( Fig. 8 a), inner and outer margins of the merus of the third maxilliped distally divergent ( Fig. 8 a), merus and dactylus of the third maxilliped not elongated ( Fig. 8 a), the distal outer angle of the first abdominal segment toothlike in both sexes ( Figs. 8 d, 9d), fused segments of male abdomen with constricted base ( Fig. 8 d), a straight G1 ( Fig. 8 e, f), the tooth from the dilated base of the G2 prominently exposed ( Fig. 8 h), and the vulvae along an imaginary line joining the posterior margin of the P2 coxae ( Fig. 9 a). In Sulaplax , the rostrum is vestigial, unilobed and deflexed ( Fig. 4 a, b), the side walls of the carapace lack teeth ( Fig. 4 a), the posterior margin of the epistome is prominently produced ( Fig. 4 b), the distal inner projection of the ischium of the third maxilliped is long and narrow ( Fig. 4 c), the inner and outer margins of the merus of the third maxilliped are subparallel ( Fig. 4 c), the merus and dactylus of the third maxilliped are not elongated ( Fig. 4 c), the distal outer angle of the first abdominal segment is protruded in males and not modified in females ( Figs. 5 d, 6d), the dilated base of the G2 does not form a prominent tooth, and the vulvae are on an imaginary line joining the anterior margin of the P2 coxae ( Fig. 6 a).

Figures

FIGURE 4. Sulaplax ensifer spec. nov.: a, carapace, dorsal view; b, carapace, frontal view; c, right third maxilliped. Female paratype, ZRC 2007.0119, 5.0 × 6.5 mm. Scale bars, 1 mm.

FIGURE 5. Sulaplax ensifer spec. nov.: a, left P 3; b, male left chela; c, female left chela; d, male abdomen-pleotelson; e, left G 1, ventral view; f, left G 1, dorsal view. a, c, female paratype, ZRC 2007.0119, 5.0 × 6.5 mm; b, d – f, male holotype,

FIGURE 6. Sulaplax ensifer spec. nov.: a, thoracic sternum of female; b – d, female abdomen-pleotelson, outer surface (b and d) and inner surface (c); e – h, second to fifth right pleopods, anterior view. a – d, female paratype, ZRC 2007.0119, 5.0 × 6.5 mm; e – h, female, MNHN-B 30396, 4.0 × 5.0 mm. Scale bars, 1 mm. Numbers and “ V ” refer to thoracic sternites and vulvae, respectively.

FIGURE 7. Guaplax denticulata spec. nov.: a, habitus; b, carapace, frontal view. a, male holotype, MZB Cru 1654 (holotype), 2.7 × 3.1 mm; b, female paratype, MNHN-B 3061, 3.4 × 4.1 mm. Scale bars, 1 mm.

FIGURE 8. Guaplax denticulata spec. nov.: a, right third maxilliped; b, male left chela; c, left P 3; d, male abdomen-pleotelson; e, left G 1, ventral view; f, left G 1, dorsal view; g, left G 2; h, G 2 on abdomen, inner view. a, female paratype, MNHN-B 3061, 3.4 × 4.1 mm; b – h, male, ZRC 2007.0120, 2.9 × 3.4 mm. Scale bars, a, e – g, 0.5 mm; b – d, h, 1 mm.

FIGURE 9. Guaplax denticulata spec. nov.: a, thoracic sternum of female; b – d, female abdomen-pleotelson, outer side (b and d) and inner surface (c); e – h, second to fifth left pleopods, anterior view. Female paratype, MNHN-B 3061, 3.4 × 4.1 mm. Numbers and “ V ” refer to thoracic sternites and vulvae, respectively. Scale bars, 1 mm.