Metasesarma H. Milne Edwards, 1853

Ng, Peter K. L. & Schubart, Christoph D., 2003, On the identities of Sesarma obesum Dana, 1851, and Sesarma eydouxi H. Milne Edwards, 1853 (Crustacea, Decapoda, Brachyura, Sesarmidae), Zoosystema 25 (3), pp. 425-437 : 426-430

Genus Metasesarma H. Milne Edwards, 1853

Metasesarma obesum ( Dana, 1851) n. comb. ( Figs 1-3 )

Sesarma obesum Dana, 1851: 252 ; 1852: 356, pl. 22, fig. 10.

Metasesarma rousseauxi H. Milne Edwards, 1853: 188 ; 1854: 158, pl. 10, figs 1, 1a-1c. — Crosnier 1965: 73, figs 116-120. — Ng & Davie 1995: 39.

Metasesarma granularis Heller, 1862: 522 .

Metasesarma rugulosa Heller, 1865: 65 .

Sesarma obesa – de Man 1887: 643.

Sesarma (Holometopus) obesa – Tesch 1917: 179.

Sesarma (Holometopus) ? obesum – Serène 1968: 107.

Chiromantes obesum – Ng & Liu 1999: 229.

MATERIAL EXAMINED. — Taiwan. Pingtung, 22.V.1998, coll. H.-C. Liu, 1, 2 ( ZRC 1998.399 ) ; Pingtung, 19.V.1998, coll. H.-C. Liu, 1 ( ZRC 1999.552 ). — Little Liu-Kiu Island , 1.VIII.1994, coll. H.-C. Liu, C. H. Wang, 1, 2 ( ZRC 1998.479 ). — Feng Chui-Sa, Pingtung, 24.VI.2002, coll. P. K. L. Ng, 1 ( ZRC) .

Guam. Pago Bay, 15-18.IV.2000, coll. P. K. L. Ng, C. H. Wang, 3, 16 ( ZRC 2000.583). — Haputo, VIII.2001, coll. P. K. L. Ng, 2, 1 ( ZRC 2001.744). — Dadi Beach, 31.VII.2001, coll. P. K. L. Ng, 2, 1 ovigerous ( ZRC 2001.749).

Tahiti. East of Papeete , 21.XI.1996, coll. G. Paulay, 1 ( ZRC 2000.582 ) ; X.2001, coll. H.-C. Liu, 2, 1 ( ZRC) .

Australia, Christmas Island. 1939, coll. C. A. Gibson- Hill, 3, 8 ( ZRC 1966.12.2.1-10).

Malaysia, Sabah. Pulau Manukan, northern Sabah, 22.VI.2000, coll. C. D. Schubart, 1, 1 ( ZRC 2000. 1656, 1657).

Indonesia. Pangandaran, 3.III.1963, coll. R. Serène, 9, 4 ( ZRC 1971.11.1.1-5), 1 ( ZRC 1971.5.3.1), 1 ( ZRC 1971.11.1.6). — Citerjun, Ujung Kulon, West Java, in leaf litter, 5 m from the shore, 30.VII.1993, coll. C. Stewart, 1 15.2 × 13.3 mm, 1 15.3 × 13.4 mm ( ZRC).

REMARKS

Dana (1851) described Sesarma obesum from a specimen originating from an island in Balabac Strait north of Borneo. Serène (1968: 107) in listing this species under Chiromantes (as Holometopus ) questioned its systematic position and indicated that it might be referred to Metasesarma . The original figure provided of Sesarma obesum by Dana (1852: pl. 22, fig. 10) is good ( Fig. 1 ) and confirms that the species should be assigned to Metasesarma . The form of the carapace and legs strongly suggests that Sesarma obesum Dana, 1851 , is identical to Metasesarma rousseauxi H. Milne Edwards, 1853 . This species is often reported from islands with wide gravel or sandy beaches without rivers or freshwater sources, as is typical for the islands north of Borneo. Numerous specimens of this species from the Indo-West Pacific have been examined, and while the colour varies according to the substrate, the lateral carapace margins of this species are typically straight and subparallel, giving the carapace a squarish appearance. In larger specimens (e.g., the proposed neotype), however, the margins are gently convex.

Specimens identified as Metasesarma rousseauxi from an island north of Sabah, relatively close to the type locality of S. obesum , the Balabac Islands (not easily accessible nowadays due to political problems) were examined. The material is comparable to the specimen figured by Dana (1852). Therefore, a male specimen from the island off Sabah was selected as the neotype of Sesarma obesum , thereby fixing the identity of this poorly known species. The neotype is a male measuring 14.3 × 13.5 mm ( ZRC 2000.1656), collected from amongst supralittoral coral rubble on Pulau Manukan, northern Sabah, East Malaysia, Borneo, on 22 June 2000 ( Figs 2 ; 3 ). This action effectively synonymises Metasesarma rousseauxi with Sesarma obesum , with the latter name having priority. Furthermore, Sesarma obesum is transferred to Metasesarma .

On the basis of the identification by the late Raoul Serène, Hartnoll (1975: 308, 322) referred specimen(s) from Tanzania with doubt to “ Holometopus obesus ”. The whereabouts of these specimens is not known ( R. G. Hartnoll pers. comm.). Whether they are what is here identified as Metasesarma obesum n. comb. (and M. rousseauxi ) cannot be ascertained. It is interesting to note, that while the type locality of M. rousseauxi is the east coast of Africa (from where it has also

14.3 × 13.5 mm ( ZRC 2000.1656), Pulau Manukan, Sabah; A,

been reported from by Crosnier [1965] and Guinot [1967], Hartnoll (1975: 307) did not find this species in Tanzania, but instead report- ed “ Holometopus obesus ” from the supralittoral area of a rocky shore. This is precisely the preferred habitat of M. rousseauxi (see Ng & Davie 1995). Consequently, Hartnoll’s material is considered to be conspecific with what is here defined as Metasesarma obesum n. comb.

In any case, the taxonomy of what has been called Metasesarma rousseauxi (type locality: Zanzibar), may not be systematically stable (see Tesch 1917: 212; Crosnier 1965: 73; Ng & Davie 1995: 39, for complete synonymy). Metasesarma granularis Heller, 1862 , and M. rugulosa Heller, 1865 , are both regarded as junior synonyms of M. rousseauxi (see Crosnier 1965; Ng & Davie 1995) and thus now of M. obesum n. comb., but considering the extensive range of the species, it is possible that this might be a species complex with more than one species involved. As such, Metasesarma rousseauxi may yet prove to be different from Sesarma obesum . But on current knowledge, there is little evidence to justify separating these two taxa. As a result, the well known supralittoral Metasesarma rousseauxi from the Indo- West Pacific should now be known as Metasesarma obesum ( Dana, 1851) n. comb. One other Metasesarma is known from the Indo-West Pacific, M. aubryi (A. Milne Edwards, 1869) , a species that normally occurs further inland in forests or close to freshwater habitats ( Ng & Davie 1995).

Figures

FIG. 1. — Sesarma obesum Dana, 1851, original figure, after Dana (1852: pl. 22, fig. 10a).

FIG. 2. — Metasesarma obesum (Dana, 1851) n. comb., neotype, overall view; B, carapace; C, frontal view.

FIG. 3. — Metasesarma obesum (Dana, 1851) n. comb., neotype, 14.3 × 13.5 mm (ZRC 2000.1656), Pulau Manukan, Sabah; A, ventral view; B, left chela, outer view; C, left chela, inner view.