Tanaocheles bidentata ( Nobili, 1901 ) Ng, 2000

Ng, Peter K. L., 2000, The Indo-Paci ® c Pilumnidae XII. On the familial placement of Chlorodiella bidentata (Nobili, 1901) and Tanaocheles stenochilus Kropp, 1984 using adult and larval characters with the establishment of a new subfamily, Tanaochelinae (Crustacea: Decapoda: Brachyura), Journal of Natural History 34, pp. 207-245 : 209-212

Tanaocheles bidentata ( Nobili, 1901) new combination

(®gures 1a±f, 2a±g, 3a±g) Chlorodius sp. Nobili, 1899: 258 (Red Sea). Chlorodius bidentatus Nobili, 1901: 15 (Red Sea); Nobili, 1906: 263 (no new locality);

Klunzinger, 1913: 219 (Red Sea). Chlorodiella bidentata, Gordon, 1934: 49 , ®g. 26b (Banda Neira); Balss, 1938: 52 (Red Sea);

Monod, 1938: 131, ®g. 20 (Suez); Forest and Guinot, 1961: 96 (no new locality); Guinot, 1967: 262 (no new locality); SereÁne, 1968: 81 (list); Chen and Lan, 1978: 269, ®gs 3, 7(8, 9) (Xisha Islands, South China Sea); SereÁne, 1984: 257, ®g. 167, pl. 36F (Palawan; Malaysia); Dai et al., 1986: 351, ®g. 168(2), pl. 45(4) (Xisha and Hainan islands, South China Sea); Dai and Yang, 1991: 339±340 pl. 45(4), ®g. 168(2) (no new locality).

Material examined. Red Sea: Jubal , one m (5.0Ö 3.2 mm), one juvenile (2.8Ö 1.8 mm) ( MNHN MP-B 8535 ), in hard coral, coll. R. Dollfus, 29 December 1928 .

Singapore: Sentosa Reefs , one, l three m ( ZRC 1984.5082 ±5085), coll. P. Ng, 25 May 1982 ; one m (ex-ovigerous) ( ZRC 1998.794 ), coll. P. Ng, 21 November 1987 ; three l(largest 8.5Ö 5.3 mm), three m (one ovigerous) (largest m, ovigerous, 8.7Ö 5.1 mm) ( ZRC 1984.5678 ±5683), coll. P. Ng, 28 April 1982 ; one m (7.3Ö 4.1 mm) ( ZRC 1987.451 ), at base of Pocillopora coral, coll. P. Ng, December 1985 ; one l (8.5Ö 4.9 mm), one m (8.0Ö 4.7 mm) ( ZRC 1998.835 ) ; Siloso Beach reefs, Sentosa, two l(largest 7.5Ö 4.5 mm), two m (largest 8.4Ö 5.1 mm) ( ZRC 1984.5082 ±5085), coll. P. Ng, 26 May 1982 ; Labrador Beach , Singapore; two l(largest 10.0Ö 5.8 mm), two m (one ovigerous) (largest 7.7Ö 4.1 mm) ( ZRC 1984.5078 ±5081), coll. P. Ng , 26 February.

Philippines: Palawan Island , one l(7.0 Ö 4.0 mm) ( ZRC 1972.8.21. 2), coll. R. SereÁ ne, June 1963 .

New Guinea: Salawatti , two l(largest 10.0Ö 5.8 mm), two m (largest 7.7Ö 4.4 mm)

( ZMB 5126), from corals, Gazelle Expedition.

Diagnosis. Anterolateral margin with two distinct spines on posterior half, anterior half with one to two small tubercles (excluding external orbital tooth); merus of chelipeds with one proximal and one subdistal spines; carpus of ambulatory legs one to three with one (rarely two, sometimes none) subdistal spines, carpus of ambulatory leg four unarmed; G1 with proximal half gently bent outwards, distal part relatively slender.

Remarks. Tanaocheles bidentata is not a xanthid s. str. because it possesses seven free male abdominal segments (three to ®ve fused in Xanthidae ), a sinuous, slender and simple G1 (stouter, less sinuous and tip often ornamented with long setae or folds in Xanthidae ) and a sigmoid G2 (relatively longer and not signoid in Xanthidae ).

All specimens of T. bidentata examined agree well with Nobili’s (1901) and SereÁne’s (1984) accounts of this species. The species was described from a single female, but the whereabouts of this Red Sea type specimen is unknown. It was not deposited in the MNHN (D. Guinot, personal communication). However, during this present study two specimens were examined (one female, one juvenile, MNHN MP-B 8535) from Suez ( Monod 1938), Red Sea and they agree well with the series of specimens from Southeast Asia. Until adult male crabs of T. bidentata from the western Indian Ocean become available for study, specimens from the Red Sea, Southeast Asia and New Guinea are regarded as conspeci®c.

Variation in the species was noted. For example, there is only one subdistal dorsal spine on the ®rst to third ambulatory carpus, but in a few specimens, there is a second much smaller, submedian spine. The fourth ambulatory carpus in all specimens is unarmed. The inner margin of the cheliped merus usually has two distinct sharp teeth, although the proximal one may be low in some specimens. The anterolateral margin is usually composed of two rounded and two spiniform teeth. The form of the spiniform teeth varies from almost straight to gently curved. The G1 is generally constant in shape, although the slender distal part in some specimens appears to be slightly longer with the tip more strongly tapering. None of these di erences can be regarded as signi®cant at the species level.

The supposed range of this species is wide, from the Red Sea to Southeast Asia, China and New Guinea, although speci®c localities are few. In Singapore it is relatively common occurring at the base of several hard branching coral species in the littoral and sublittoral reefs. Tanaocheles bidentata is frequently collected with the xanthid Chlorodiella nigra , it occurs in heterosexual pairs and although one coral head may have several pairs, they have never been found free-living.

In life, the dorsal surfaces of the carapace, legs and chelipeds are ebony black.