Thecaplax, Ng & Rahayu, 2014

Ng, Peter K. L. & Rahayu, Dwi Listyo, 2014, Revision of the family Acidopsidae Števčić, 2005, and the systematic position of Typhlocarcinodes Alcock, 1900, Caecopilumnus Borradaile, 1902, and Raoulia Ng, 1987, with descriptions of two new genera and five new species (Crustacea: Brachyura: Goneplacoidea), Zootaxa 3773 (1), pp. 1-63 : 50

Thecaplax gen. nov.

Diagnosis. Carapace subquadrate; dorsal surface convex, granular, setose; regions separated by deep grooves; front entire, margin rounded, lined with setae obscuring margin; anterolateral margin arcuate, granular, hirsute, cut into 3 distinct broad lobes, margin with several small, large teeth, lined with dense setae which obscures margin; anterolateral margins separated from gently converging posterolateral margins. Epistome narrow, prominently sunken. Basal antennal 3 rectangular, longer than wide; article 4 dorsoventrally flattened, twice as long as broad, margins with numerous long plumose setae. Basal antennular article subovate; antennules folding almost vertically. Eyes immobile, pear-shaped, tapering to small cornea, cornea not pigmented. Third maxillipeds relatively short, stout, closing buccal cavern completely; merus subquadrate, anterolateral angle rounded; exopod relatively narrow, with long flagellum. Outer surface of palm covered by numerous large tubercles, granules. Propodus, dactylus of last ambulatory leg long. Male thoracic sternum relatively wide, st1, 2 completely fused to form subtriangular plate, st3, 4 visibly separated by shallow but distinct oblique grooves joining at end of sterno-abdominal cavity; sterno-abdominal cavity reaching to imaginary line joining base of coxae of chelipeds; penis sits exposed in distinct groove between st7, 8; large part of st8 exposed when abdomen closed, broadly rectangular in shape; pressbutton mechanism for holding male abdomen present as small rounded tubercle on anterior third of st5. Male abdomen with a1 reaching to cx5, lateral parts tapering to sharp edge, somite appearing subtriangular; lateral margin of a3 produced, forming triangular structure; a3–5 fused, with sutures shallow but visible. Gl relatively stout, distal surfaces with numerous spinules; G2 as long as G1, distal segment half length of proximal segment.

Etymology. The name is derived from the Latin theca for “box,” together with - plax, a common suffix for goneplacoid genera. Gender feminine.

Remarks. The external features of Thecaplax capillosa gen. et sp. nov. are similar to those of Caecopilumnus , and in the subquadrate carapace, it comes closer to C. hirsutus Borradaile, 1902 . It can immediately be distinguished, however, by its more prominently cut anterolateral teeth, which are separated by deep clefts. More importantly, the condition of the penis and abdomen are very different. In Thecaplax gen. nov., the posterior thoracic sternum is relatively wider, with the exposed penis sits in a long continuous groove that extends from cx5 to the sterno-abdominal cavity ( Fig. 34D ) (a narrower posterior thoracic sternum, and st7 and st8 adjacent next to cx5 and partially protecting the penis, with the rest of it sitting in a short exposed groove in Caecopilumnus ; Fig. 1E, F ). The lateral edges of a1 of Thecaplax gen. nov. are also sharply tapering to form acutely triangular structures ( Figs. 34D , 35A ), whereas in Caecopilumnus , a1 is subrectangular, with the lateral margins almost straight or gently convex ( Figs. 1E , 27A ).

Figures

FIGURE 1. Male thoracic sterna, abdomens and sterno-abdominal cavities. A, B, Acidops cessacii (A. Milne-Edwards, 1878), male (11.3 × 8.1 mm) (ZRC 1998.58), Ascension; C, D, Parapilumnus cristimanus (A. Milne-Edwards, 1873), male (16.3 × 12.5 mm) (ZRC 2003.90), Nansha Is. (Spratly Is.), South China Sea; E, F, Caecopilumnus crassipes (Tesch, 1918), male (11.8 × 10.1 mm) (ZRC 2013.1710) Lombok, Indonesia; G, H, Raoulia fortis sp. nov., holotype male (12.0 × 9.2 mm) (MNHN), Santo, Vanuatu. Abbreviations: a1–5 = male abdominal somites 1–5, respectively; cx4, 5 = coxa of fourth and fifth ambulatory leg, respectively; p = penis; st7, 8 = thoracic sternites 7 and 8, respectively.

FIGURE 27. Caecopilumnus hirsutus Borradaile, 1902, male (7.1 × 5.6 mm) (ZMA 261027), Flores, Indonesia. A, male abdomen; B, C, left G1. Scales: A = 0.5 mm; B, C = 0.25 mm.

FIGURE 34. Thecaplax capillosa gen. et sp. nov., holotype male (11.6 × 9.5 mm) (MZB), Lombok, Indonesia. A, dorsal view; B, anterior thoracic sternum and sterno-abdominal cavity; C, frontal view of carapace; D, posterior thoracic sternum; E, outer view of right chela; F, outer view of left chela.

FIGURE 35. A–H, Thecaplax capillosa gen. et sp. nov., holotype male (11.6 × 9.5 mm) (MZB), Lombok, Indonesia; I, paratype female (12.7 × 10.5 mm) (ZRC 2013.1714), Lombok, Indonesia. A, male abdomen; B, left third maxilliped; C, frontal view of carapace showing antennules, antennae, epistome and orbit; D, E, left G1; F, G, distal part of left G1; H, left G2; I = female abdomen. Scales: A–C, I = 1.0 mm; D, E, G = 0.5 mm; F, G = 0.1 mm.