Guaplax denticulata, 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 : 33-38

Guaplax denticulata spec. nov.

( Figs. 7–9 )

Material examined. Holotype. Male, 2.7 × 3.1 mm, MZB Cru 1654, Gua Laowacling, Tabalar ulu, Kalimantan Timur, Indonesia, coll. C. Rahmadi & L. Deharveng, 11 Aug. 2004.

Paratypes. One male, 2.9 × 3.4 mm, ZRC 2007.0120, data same as holotype; 1 female, 3.4 × 4.1 mm, MNHN-B3061, data same as holotype.

Description. Carapace ( Fig. 7 ) subcircular, slightly wider than long, CW 1.17–1.20 times (n = 3) CL; dorsal surface flat, surrounded by continuous rim, regions clearly separated by grooves, cervical groove branching near distal end, branches confluent with rim; rostrum separated from carapace by rim, trilobate, median tooth slightly longer than, and placed inferior to, lateral teeth, teeth proximally fused; anterior margin of cephalothorax produced anteriorly in lateral view; anterolateral margin with 4 rounded teeth on dorsal rim, first to third teeth equidistantly placed, fourth tooth just behind third tooth, side wall below posterolateral margin gently swollen laterally, with two flat, triangular teeth. Antennular fossae very shallow, medially separated by thin, very low septum; a rounded tubercle on outwards of eye. Eye ( Fig. 7 ) slightly visible from dorsal view, base of ocular peduncle fused to orbit, immovable, with conical tip, cornea without trace of black pigment. Epistome with posterior margin straight, cristate, slightly upturned.

Third maxillipeds ( Fig. 8 a) narrow, forming wide gape between endopods; exopod long, reaching just proximal to distal end of merus, with cylindrical flagellum; ischium short, with wide distal inner extension; merus ovoid, midlength about 1.5 times length of ischium; dactylus slender, slightly longer than propodus, distal end reaching distal inner part of ischium in situ.

Female with circular vulvae ( Fig. 9 a), vulvae not raised, located on imaginary line joining posterior ends of P2 coxae on medial fused plate of thoracic sternum. Chelipeds symmetrical in both males and females, slightly larger in males; merus curving inwards, with flat ventral surface, ventral margins rounded, ventral outer margin without tooth; carpus slightly shorter than dorsal length of palm, outer surface rounded, without inner angle; palm of chela ( Fig. 8 b) with swollen outer surface, as long as dactylus; fingers straight, distal part slightly incurving backwards, with crossing acute tips, cutting edges with tiny teeth.

Ambulatory legs ( Figs. 7 a, 8c) thin, moderately long; P3 and P4 subequal in length, longer than P2, P5 not clearly shorter than others; meri with elliptical cross-section, with constant diameter throughout length, P3 and P4 meri shorter than carapace length and width of dorsal rim, with rounded thin projection on distal anterior angle; propodi shorter than respective meri; dactyli clearly shorter than propodi, slightly incurved, inner margin lined with short setae, ending in sharp spine, without subterminal tooth.

Male abdomen-pleotelson ( Fig. 8 d) 4 segmented, third to fifth abdominal segments fused; first segment with proximal part placed below posterior part of carapace, disto-lateral angles forming cylindrical lobe, lobe extending beyond distal margin of median part of first segment; second segment short, narrower than first and fused segments; fused segments with narrow proximal margins, slightly wider than distal margins, lateral margins of proximal half convex, distal half narrowed, slightly concave; pleotelson tong-shaped, with convex proximal margin distinctly narrower than half width of abdomen. G1 ( Fig. 8 e, f) almost straight, tapering simply, dorsal side of inner margin of distal part lined with long, stiff setae; suture running from dorsal side of proximal part to outer margin of distal part. G2 ( Fig. 8 g) short, with dilated base, proximal outer part protruded from lateral margin of second abdominal segment, partially visible in dorsal view ( Fig. 8 h).

Female abdomen-pleotelson ( Fig. 9 d) rounded, second segment to pleotelson fused, first segment with proximal part placed below posterior margin of carapace, disto-lateral angles forming rounded teeth; second segment short, boundaries between second and third and between fifth and pleotelson demarcated only by shallow sutures externally; inner surface of abdomen covered with thin membrane, forming pouch; pleopods present on second to fifth segments, biramous, short, contained inside pouch.

Etymology. From the Latin denticulatus meaning “bearing small teeth”, alluding to the teeth on the carapace. The name is used as an adjective.

Remarks. Apart from the generic characters separating Guaplax from Sulaplax , Guaplax denticulata spec. nov. can be immediately differentiated from S. ensifer spec. nov. by possessing moderately long ambulatory legs ( Figs. 7 a, 8c) (relatively much longer in S. ensifer , fig. 3, 5a) and the presence of anterolateral and posterolateral teeth on the carapace ( Fig. 7 a, b) (absent in S. ensifer , fig. 4a, b). Guaplax denticulata can be also distinguished from S. ensifer by the relatively shorter fingers of the chelae, with the immovable finger slightly longer than the length of the palm ( Fig. 8 b) (clearly longer in S. ensifer , fig. 5b, c), the absence of a subdistal tooth on the ventral outer margin of the cheliped merus (present in S. ensifer ), a long male pleotelson having convex proximal margin ( Fig. 8 d) (relatively shorter, with straight proximal margin in S. ensifer , Fig. 5 d), and the straight G1 ( Fig. 8 e, f) (curving outwards at half in S. ensifer , fig. 5e, f).

The only female specimen of G. denticulata (MNHN-B30397, 3.4 × 4.1 mm) has a torn thoracic sternum ( Fig. 9 a). Ng & Chuang (1996: 60, figs. 25, 26) observed that the zoeae of N. mangalis (Ng, 1988) hatched inside the internal brood cavity and left their mother from a pair of “pseudovulvae” at thinly chitinised posterior part of the thoracic sternal cuticle. The true vulvae are too small for zoeae to come out. Naruse et al. (2005) also reported that the zoeae of N. yaeyamaensis Naruse, Shokita & Kawahara, 2005 , were released from the pseudovulvae when the abdomen of the preserved specimen was opened. As such, the torn thoracic sternum of the female specimen of G. denticulata might have been caused by a recent release of its eggs, larvae or juveniles. Such an internal brood cavity is possible in the Hymenosomatidae because there is a vacuum in the central part of the body, that is devoid of endosternites and endopleurites in the whole median part (except the sella turcica, posteriorly), the phragmae being only located on lateral sides of the body and leaving an empty place. The sternal wall is thus strongly depressed, even reaching the dorsal wall of the carapace (Guinot & Richer de Forges 1997: 474, 477, figs. 2C, E, 6F).

TABLE 1. Key characters of cave-dwelling hymenosomatid genera and allied genera.

Sulaplax gen. nov. Guaplax gen. nov. Neorhynchoplax Cancrocaeca Limnopilos

Rostrum Unilobed, deflexed, Trilobed, developed Unilobed or trilobed, Absent Vestigial or absent

vestigial developed

Anterior surface of Vertical Relatively vertical Strongly projecting Relatively vertical Relatively vertical

cephalothorax (in lat- beyond rest of ceph-

eral view) alothorax

Configuration of the Located at outer Located at lower Located at just inner Located at just inner Located at just

base of basal anten- lower region with region with respect lower region with lower region with inner region with

nal article against respect to base of to base of ocular respect to base of respect to base of respect to base of

base of ocular pedun- ocular peduncle peduncle ocular peduncle ocular peduncle ocular peduncle

cle

Dorsal surface Well defined Well defined Well defined Poorly defined Well defined

regions

Eyes Fused to orbit, Fused to orbit, Complete Fused to orbit, Complete no pigment no pigment no pigment

Longitudinal groove Absent Absent Absent Present Present

on side wall of cara-

pace

Female vulvae On imaginary line On imaginary line On various parts on On imaginary line On imaginary line joining anterior mar- joining posterior medial fused plate of joining bases of P3 joining sutures gins of P2 coxae on margins of P2 coxae thoracic sternum on medial fused between sternites 5 medial fused plate of on medial fused (from level of poste- plate of the thoracic and 6 on medial thoracic sternum; plate of thoracic ster- rior margins of P1 sternum; with basal fused plate of the without basal mount num; without basal coxae to anterior mount thoracic sternum; mount margins of P3 coxae) with basal mount (confirmed except for L. microrhynchus )

Ambulatory dactyli: Absent Absent Present or absent Absent Present

subterminal tooth

Male abdomen-pleo- 4 segmented (3rd–5th 4 segmented (3rd– 4–5 segmented (3rd– 6 segmented (no 6 segmented (no

telson fused); pleotelson 5th fused); pleotel- 5th or 4th–5th fused) fusion), barreled; fusion), barreled; narrow, distinctly less son narrow, dis- [see Ng & Chuang pleotelson wide, pleotelson wide, than half of maxi- tinctly less than half 1996]; pleotelson more than half of more than half of mum width of abdo- of maximum width narrow, distinctly maximum width of maximum width of men; fused segment of abdomen; fused less than half of abdomen abdomen with proximal part segment with proxi- maximum width of

not constricted mal part constricted abdomen

Female abdomen-ple- 1st–2nd and 2nd–3rd 1st–2nd movable, 3rd–5th, 2nd–5th, or 6 demarcated seg- 6 distinctly demar-

otelson segmented, 3rd–pleo- 2nd–3rd and 5th– 2nd-pleotelson fused ments, boundary cated segments, telson fused, 5th–ple- pleotelson only with between 1st and 2nd boundary between otelson with suture suture on outer side. movable 1st and 2nd or on outer side only between 2nd and 3rd segments movable

to be continued... table 1 continued...

Female pleopods 2nd–5th present, 2nd–5th present, Present in some spe- Biramous, setose, Biramous, setose, biramous, short, biramous, short, cies (e.g. N. manga- long plumose pleo- plumose long pleowithin pouch within pouch lis, unpubl. data) pods developing pods developing from distal outer from distal outer angle of inner sur- angle of inner surface of 2nd–5th face of 2nd– 5th abdominal segment abdominal segment (not observed in L. microrhynchus )

G1 Bent at half, tapering, Straight, tapering, tip Distal portion Stout, bent and Stout, bent and tip simple simple curved, tapers to twisted on proximal twisted on proximal simple tip 1/4, with processes 3/5, with processes on apex on apex

Brooding of eggs Internal brood cavity Internal brood cavity Internal brood cavity Eggs brooded within Eggs attached to inner surface of endopods; exopods dome-shaped abdo- extending inwards, men, not attached to partially covering endopods; 3rd–5th “dome” (not exopods lie along observed in L. lateral margin of microrhynchus ) abdomen, covering

margin of “dome”

Habitat Freshwater in caves Freshwater in caves Intertidal flat to Freshwater in caves Brackish-water freshwater environments environments

Figures

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 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.