Tanaocheles bidentata ( Nobili, 1901 )

Padate, Vinay P., Periasamy, Rengaiyan, Rivonker, Chandrashekher U. & Ingole, Baban S., 2023, Coral reef-associated brachyuran fauna (Crustacea: Decapoda: Brachyura) from Angria Bank off the west coast of India, Zootaxa 5357 (3), pp. 398-422 : 402-403

Tanaocheles bidentata ( Nobili, 1901)

( Fig. 3A–E )

Chlorodius sp. — Nobili 1899: 258.

Chlorodius bidentatus Nobili, 1901: 15 (type locality: Red Sea).— Nobili 1906a: 263.— Klunzinger 1913: 219 (123).

Chlorodiella bidentata .— Gordon 1934: 49, fig. 26b.— Balss 1938: 52.— Monod 1938: 131, fig. 20.— Forest & Guinot 1961: 96.— Guinot 1967: 262.— Serène 1968: 81.— Chen & Lan 1978: 269, fig. 3, 7 (8–9), pl. 1, fig. 3.— Serène 1984: 22 (list) 254 (key), fig. 167, pl. 36F.

Tanaocheles bidentata .— Ng & Clark 2000: 209–212, figs. 1a, c–f, 3a–e.

Material examined. 2 males (4.8 × 3.0 mm, 4.7 × 2.9 mm) ( NIO /BOD/AB/BRY/00007), RVSS 7 , west of Vijaydurg , Arabian Sea, 16.38°N, 72.17°E, 27 m depth, Van Veen grab, coll. R. Periasamy, 7 January 2014 .

Diagnosis. Carapace subhexagonal, broader than long, dorsal surface smooth, regions poorly defined; frontal margin sinuous, separated from inner supraorbital tooth by deep notch accommodating antennal flagellum; external orbital tooth small; anterolateral margin (behind external orbital angle) with 1 blunt projection followed by 2 anteriorly directed claw-like teeth, second tooth larger; posterolateral margin strongly converging ( Fig. 3A ). Endostomial ridges well developed throughout their length. Basal antennal article large, rectangular. Maxilliped 3 merus sub-quadrate, shorter than ischium, antero-external angle rounded ( Fig. 3B ). Chelipeds unequal, sub-cylindrical, smooth; larger cheliped with acuminate dactylus, carpus with blunt spine at inner angle; merus with blunt sub-distal and sub-proximal spinule on anterior margin ( Fig. 3C ). Male pleon of 6 somites and telson ( Fig. 3D ). G1 S-shaped, with proximal half relatively stout, distal part sinuous and slender ( Fig. 3E ).

Colouration. Preserved specimen: light brown with scattered black spots ( Fig. 3A ), cheliped brownish, fingers dark brown with white tips ( Fig. 3C ).

Biology. Known to be a symbiont on the corals Acropora, Dendrophyllia ( Serène 1984) and Pocillopora in littoral and sub-littoral reefs ( Ng & Clark 2000); occurs in heterosexual pairs, and probably associated with the xanthid crab, Chlorodiella nigra ( Ng & Clark 2000) . The present specimens were collected from sandy substrate, at 27 m depth, in the vicinity of live corals.

Remarks. Nobili (1901) described C. bidentatus from the Red Sea and included it in the Family Xanthidae . Serène (1984) suggested the transfer of C. bidentata to a separate genus owing to the differences in carapace, cheliped and gonopod morphology with its existing congeners. Ng & Clark (2000) reviewed the taxonomy of T. bidentata and proposed its transfer from Xanthidae to a new pilumnid subfamily Tanaochelinae owing to differences in larval and adult morphological characters. The Indian specimens conform to the description of the holotype provided by Nobili (1901) in the smooth, flat dorsal carapace without areolated regions, the presence of two spiniform anterolateral teeth, the cheliped with 2 spines on the anterior margin of merus, a large inner carpal spine, smooth elongated propodus and short moderately arched fingers.

Geographical distribution. Red Sea, Singapore, Malaysia, China, Philippines, New Guinea ( Serène 1984; Ng & Clark 2000); eastern Arabian Sea off India (present study). The present observation is the first record from Indian waters.

Figures

FIGURE 3. Tanaocheles bidentata (Nobili, 1901), male (NIO/BOD/AB/BRY/00007, 4.7 × 2.9 mm), eastern Arabian Sea, India: (A) carapace, dorsal view; (B) left maxilliped 3, external view; (C) right cheliped, dorsal view; (D) cephalothorax, ventral view; (E) G1, pleonal view. Cycloachelous granulatus granulatus (H. Milne Edwards, 1834), male (NIO/BOD/AB/BRY/00008, damaged specimen), eastern Arabian Sea, India: (F) dorsal habitus (fresh colour); (G) ventral habitus (fresh colour). Portunus convexus De Haan, 1835, juvenile (NIO/BOD/AB/BRY/00009, damaged specimen), eastern Arabian Sea, India: (H) dorsal habitus (fresh colour). Scale bars: A–E, 1 mm. F–H, 5 mm.