Contusarma bocourti
Creators: name: Schubart, Christoph D.
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Contusarma
Contusarma bocourti

description: Contusarma bocourti (A. Milne-Edwards, 1869)
(Figs. 23A–C, E, F, 25H, 28 A–C, 31 A, 38, 44 G, 57 A)
Sesarma bocourti A. Milne-Edwards, 1869: 28.
Sesarma (Sesarma) bocourti – Tesch, 1917: 135 (part).
Pseudosesarma bocourti – Naiyanetr, 1998: 101; Naiyanetr, 2007: 17 (unnumbered fig.), 115; Ng et al., 2008a: 222; Hoang et al., 2012: 75, 78.
Material examined. Lectotype (here designated): male (24.0 × 27.2 mm) (MNHN D-10965), Bangkok, Thailand. Paralectotype: male (19.1 × 21.5 mm) (MNHN D-10965), same data as lectotype. THAILAND – male (25.3 × 23.3 mm) (ZRC 2000.0952), Silom, Chao Phraya at cemetery, Hotel Mae-Noon, Bangkok, coll. Pongsathron, 1 August 1998; 1 female (ZRC 2019.1114), Bangkok, Thailand, from aquarium trade, via C. Lukhaup, 9 January 2007.
Diagnosis. Anterior dorsal carapace regions with relatively dense short black setae; outer surface of adult chela covered with large flattened granules, those on margins large, sharp; margins of ambulatory segments with dense short setae; male pleon relatively transversely more narrow; G1 relatively stouter, chitinous distal part gently curved, proportionately wider.
Colour. Carapace relatively dark, gastric regions almost black; distal margins of ambulatory merus, carpus, and propodus with darker bands (Fig. 57A) (see also Naiyanetr, 2007: 17, unnumbered fig.).
Remarks. Sesarma bocourti was described briefly by A. Milne-Edwards (1869) from an unspecified number of specimens from Bangkok, Thailand. The extant specimens (all dried) are therefore syntypes. The largest male (24.0 × 27.2 mm, MNHN D-10965) is here selected as the lectotype of the species (Fig. 23A). Sesarma cheirogona Targioni Tozzetti, 1877, was described on the basis of a single male (22.0 × 20.0 mm) supposedly collected from Yokohama in Japan. Nobili (1900: 507) apparently examined the holotype of Sesarma cheirogona and commented that there were no significant differences from his specimens of Sesarma bocourti from Sumatra collected by the Siboga Expedition and synonymised both species. Tesch (1917) agreed with the synonymy but noted there were two types of male pleons for what had been called S. bocourti in Southeast Asia; one relatively more narrow (Tesch, 1917: fig. 2a; from an unspecified location in Borneo and Deli, Sumatra) and one relatively wider (Tesch, 1917: fig. 2b; from Balikpapan, Borneo). He, however, recognised just one species as he commented that they were otherwise similar externally. Urita (1926: 20) recorded S. bocourti from “near coast of Kagosima, Satuma” in Japan, but no material was indicated, and no figure was provided so its identity cannot be confirmed. Sakai (1939: 685; 1976: 661) listed the species for the Japanese fauna but noted that it was based on Targioni Tozzetti’s (1877) record and he had no specimens. Tweedie (1940) discussed this and commented that broader pleons are generally associated with smaller specimens and the differences were probably due to variation. Tweedie (1940: 91) also commented that “If Sesarma cheirogona Targioni Tozzetti from Yokohama (1877, p. 141) is really identical with bocourti, I am inclined to think that the specimen was wrongly localised. It was collected during the world cruise of the ‘Magenta’, which included visits to Borneo and Sumatra”. There have thus been no reliable confirmed records of this species north of Thailand, despite intensive collecting and study of crabs in Japan. This supports Tweedie’s suggestion that the type locality is likely to have been from the Indo-Malayan region rather than Yokahama.
Examination of the present extensive collection has revealed differences between the specimens from Thailand and the rest of Southeast Asia (southern Peninsular Malaysia, Singapore, and Sarawak). Most significantly, their G1s are slightly different, with those from Thailand being relatively stouter, with the chitinous distal part gently curved and proportionately wider (Fig. 38D–H). Those from the rest of Southeast Asia are relatively more slender, and the chitinous distal part is straight and proportionately narrower (Fig. 39F–J, L–N). In addition, while the male pleon does have a degree of natural variability in proportions, as discussed by Tweedie (1940), that of Thai specimens is still relatively transversely narrower (notably somite 6) (Fig. 38C) compared to those from the rest of Southeast Asia (Fig. 39E, O–Q). The adult male from Thailand is also distinctly more setose over the whole carapace and ambulatory legs (Fig. 23B, F), with the granules on the chelae proportionately stouter and larger (Fig. 28A–C). Those from the rest of Southeast Asia have sparsely setose to almost glabrous carapaces and legs (Fig. 23G, H), and the granules on the chelae are smaller (Fig. 28D). The degree of setation is not discernible on the types of C. bocourti (Fig. 23A, E), but the setae may have fallen off due to their age and dried condition. The phylogenetic tree supports this, with a sister-group relationship between the two species (Fig. 59).
While we have no doubt that the Thai material is Contusarma bocourti s. str., Hoang et al.’s (2012) material of “ Pseudosesarma bocourti ” from southern Vietnam should be re-examined if possible. It is provisionally identified as C. bocourti. The identity of the Malaysian, Singapore, and Bornean specimens is more problematic. This is because the real origin of Sesarma cheirogona is unclear, as discussed above. Tweedie (1940) commented that Targioni Tozzetti’s (1877) material of S. cheirogona could have originated from Borneo or Sumatra, but that expedition also visited Singapore, Java, and Vietnam; before the vessel reached Japan. Comparing the figures given in Targioni Tozzetti (1877), however, it seems likely his material came from Singapore or Borneo (or adjacent areas) as his figure (Fig. 39C; Targioni Tozzetti, 1877: fig. 2d) shows a proportionately wider pleon similar to those from this area (Fig. 39E, O–Q). For this reason, we refer all the present material from Peninsular Malaysia, Singapore, and Sarawak to C. cheirogonum. The identity of the specimen figured by Tesch (1917: 138, fig. 2b) with a very wide male pleon from Balikpapan in eastern Kalimantan in Borneo cannot be ascertained without a re-examination at a future date. This may simply be intraspecific variation because one specimen from Sarawak has a similarly proportioned male pleon (Fig. 31C), with the other male specimens from this location having narrower pleons. The records from the rest of Borneo and Sumatra by De Man (1880, 1895), Miers (1880), Nobili (1900), Tesch (1917), and Roux (1933) are also provisionally referred to C. cheirogonum.
The types of Targioni Tozzetti (1877) are lost. Lucas (1981: 200) notes that “The type specimens which were kept in the Museo Zoologico de “La Specola”, Firenze, Italy, are not extant; they were lost during World War II (M. Poggesi, pers. comm.)”. Gianna Innocenti (Universitá di Firenze) conducted a fresh search in 2019 but also came to the conclusion the type of Sesarma cheirogona is no longer extant. To stabilise the taxonomy of the two species in Contusarma, we here select a male (24.5 × 21.5 mm) (ZRC 1995.225) from Bako National Park, Sarawak, as the neotype of Sesarma cheirogona Targioni Tozzetti, 1877. This is necessary to stabilise the taxonomy of the species.
Biology. Probably very similar to Contusarma cheirogonum (see below), but detailed data or field observations are not available. One recent specimen (ZRC 2000.0952) was obtained from along the Chao Phraya River, from Silom, a site about 20 km from the sea. This is in the main city area of Bangkok but there is still strong tidal influence.
Distribution. Known only from western coast of Thailand, Indian Ocean.
description: Published as part of Schubart, Christoph D. & Ng, Peter K. L., 2020, Revision of the intertidal and semiterrestrial crab genera Chiromantes Gistel, 1848, and Pseudosesarma Serène & Soh, 1970 (Crustacea: Brachyura: Sesarmidae), using morphology and molecular phylogenetics, with the establishment of nine new genera and two new species, pp. 891-994 in Raffles Bulletin of Zoology 68 on pages 954-958, DOI: 10.26107/RBZ-2020-0097, http://zenodo.org/record/5351295