Tacitotheres glaber ( Bürger, 1895 ) Ng & Ahyong & Campos, 2019

Ng, Peter K. L., Ahyong, Shane T. & Campos, Ernesto, 2019, Two new genera of pinnotherid crabs (Crustacea: Brachyura: Pinnotheroidea) from the Americas and the Western Pacific, Raffles Bulletin of Zoology 67, pp. 337-351 : 346-349

Tacitotheres glaber ( Bürger, 1895) new combination

( Fig. 9 , 10 )

Pinnotheres glaber Bürger, 1895: 379 , pl. 9: fig. 23, pl. 10: fig. 21; Tesch, 1918: 248; Miyake, 1939: 221, 241; Silas & Alagarswami, 1967: 1199, 1216; Ng & Manning, 2003: 902.

Pinnotheres impressus Bürger, 1895: 380 , pl. 9: fig. 24, pl. 10: fig. 23; Tesch, 1918: 249, 255; Silas & Alagarswami, 1967: 1200, 1216.

Orthotheres glaber – Ahyong & Ng, 2007a: 218, fig. 24; Ng et al., 2008: 250.

Material examined. Lectotype: USNM 32431 , ovigerous female (7.8 × 6.5 mm), Palau, from Tapes turgida , coll. C. Semper. Paralectotypes: SMF-ZMG 173, Go304a, 6 males (3.4 × 3.1 to 4.8 × 4.3 mm), 4 females (3.5 × 3.5 to 8.3 × 7.4 mm), same locality as lectotype .

Diagnosis. Female: Carapace subcircular, slightly wider than long, front faintly projecting, convex. Eyes small, not visible in dorsal view. MXP3 with propodus more than twice as long as high, apex rounded; dactylus inserting subdistally, outreaching propodal apex; ischiomerus exceeding twice length, outer margin convex, inner margin with proximal ¾ concave, angular at distal quarter; exopod outer margin convex, inner margin relatively straight, flagellum 2-segmented. Cheliped with dactylus about 2/3 palm length; palm 2½ times as long as high, mesioventral margin setose; dactylus occlusal margin finely setose, with large proximal tooth; pollex occlusal margin sinuous, sparsely setose. Ambulatory legs asymmetrical in length from right to left; propodi broadening distally; relative lengths P3>P4>P2>P5. P2–P5 dactyli sparsely setose, shorter than half-length of respective propodi; relative lengths P3>P4>P2>P5. P4 and P5 propodus with sparse ventral setae. Pleon extending to buccal region and covering bases of ambulatory legs. Male: Carapace rounded, wider than long, front projecting, medially emarginate. Eyes visible in dorsal view. MXP3 as in female, but sometimes with small distinct tooth at inner distal angle of ischiomerus. Cheliped robust; dactylus almost as long as palm; palm almost as high as long, outer surface with shallow, irregular pits; dactylus occlusal margin with prominent, blunt proximal tooth, distal margin crenulate, sparsely setose; pollex occlusal margin finely dentate, sparsely setose; mesial margin of carpus setose. Ambulatory legs dorsally and ventrally unarmed, length asymmetrical from left to right; relative lengths P3>P2>P4>P5. Dactyli shorter than half-length of respective propodi; P2–P4 dactyli subequal in length and slightly longer than P5 dactylus. P3 and P4 propodus with dorsal and ventral setae; carpus with diagonal setal row. Pleon widest at somites 3 and 4, tapering distally to evenly rounded telson. G1 slender, arcuate. G2 with exopod distinctly longer then endopod. (Modified from Ahyong & Ng, 2007a: 218).

Remarks. It is somewhat surprising that T. glaber is known only from the type material given that it was originally reported from venerid clams, which are widely collected for human consumption. The original host, Tapes turgida ( Lamarck, 1818) is currently a junior synonym of T. conspersus ( Gmelin, 1791) . An unusual aspect of male T. glaber is the size of the G2 exopod and pleonal form. The G2 exopod of T. glaber is remarkable as it is the largest known of any pinnotherid (relatively), being about quadruple the length of the endopod ( Fig. 10L ). A large G2 exopod is also present in Viridotheres takedai Ahyong, Komai & Watanabe, 2012 , and V. kupang Ahyong, 2019 , but the exopod is shorter than three times the length of the endopod. Of note is also the form of the male pleon. Unusually, the male pleon in T. glaber is narrowest in the smallest specimens ( Fig. 10I ) becoming wider with increasing body size ( Fig. 10J ), potentially becoming more female-like. The significance of this phenomenon is presently unknown and must await further collections allowing assessment of developmental changes.

Figures

Fig. 9. Tacitotheres glaber (Bürger, 1895) new combination, A, paralectotype male (4.6 × 4.2 mm) (SMF-ZMG 173); B, C, lectotype ovigerous female (7.8 × 6.5 mm) (USNM 32431), Palau. A, B, overall dorsal habitus; C, ventral surface of cephalothorax.

Fig. 10. Tacitotheres glaber (Bürger, 1895) new combination, A–E, lectotype female (7.8 × 6.5 mm) (USNM 32431), Palau; F–I, paralectotype male (4.0 × 3.6 mm) (SMF-ZMG 173); J–M, paralectotype male (4.6 × 4.2 mm) (SMF-ZMG 173). A, F, dorsal overall habitus; B, sternum, anterior margin; C, anterior cephalothorax; E, H, right MXP3; D, G, right chela, outer view; I, J, male pleon; K, left G1, pleonal view; L, left G2, pleonal view, with long exopod; M, left MXP3. A, D–I, modified after Ahyong & Ng (2007a: fig. 24). Scale: A = 2 mm; B–D, F–G, I, J = 1.0 mm; E = 0.5; H, K, L, M = 0.25 mm.