Geosesarma amphinome (De Man, 1899 )

Ng, Peter K. L., 2015, Semiterrestrial crabs of the genus Geosesarma De Man, 1892 (Crustacea, Brachyura, Sesarmidae) from western Borneo, Indonesia, with descriptions of three new species, Zootaxa 4048 (1), pp. 37-56 : 38-41

publication ID	https://doi.org/ 10.11646/zootaxa.4048.1.2
publication LSID	lsid:zoobank.org:pub:97BB73FF-9D62-4A15-B09C-0F570E26E738
DOI	https://doi.org/10.5281/zenodo.6121300
persistent identifier	https://treatment.plazi.org/id/1B6F879D-E151-BD69-54A1-FC91DEB18A65
treatment provided by	Plazi
scientific name	Geosesarma amphinome (De Man, 1899 )
status

Treatment

Geosesarma amphinome (De Man, 1899) View in CoL

( Figs. 1 View FIGURE 1 , 2 View FIGURE 2 )

Sesarma (Sesarma) amphinome De Man, 1899: 133 View in CoL , pl. 12 fig. 16; Tesch 1918: 129 (list); Serène 1968a: 1087 (list); Serène 1968b: 106 (list).

Geosesarma amphinome View in CoL — Serène & Soh 1970: 402 (list); Ng 1988: 119 (list); Fransen et al. 1997: 123; Ng et al. 2008: 220 (list).

Material examined. Lectotype: female (11.1 × 8.5 mm) ( NNM 1198), Sintang, Borneo, coll. M. Moret, 1893– 1894. Paralectotypes: 2 males (larger 14.4 × 8.7 mm), 1 female ( NNM 23283), same data as lectotype.

Diagnosis. Carapace subtrapezoidal, wider than long, width to length ratio 1.3–1.6, lateral margins gently diverging ( Figs. 1 View FIGURE 1 A, B, 2A); dorsal surface with visible regions, anterior regions densely covered with low, small rounded, flattened granules ( Fig. 1 View FIGURE 1 A–D); front deflexed, frontal lobes broad with subtruncate margins; postfrontal, postorbital cristae low but distinct ( Fig. 1 View FIGURE 1 C, D); external orbital tooth acutely triangular, directed obliquely, outer margin gently convex to almost straight, tip extending beyond lateral margin ( Figs. 1 View FIGURE 1 A, B, 2A). Merus of third maxilliped subovate, subequal in length to ischium; exopod slender with long flagellum ( Fig. 2 View FIGURE 2 B). Outer surface of palm of adult male covered with small rounded granules; inner surface with transverse comb-like ridge; dorsal margin of dactylus with cluster of small rounded granules on proximal part, 3 or 4 slightly larger granules after it, unarmed on distal half ( Figs. 1 View FIGURE 1 F, 2F). Ambulatory legs with relatively slender merus, with sharp subdistal spine on dorsal margin, surfaces gently rugose ( Figs. 1 View FIGURE 1 A, B, 2D). Male abdomen triangular; somite 6 wide, with convex lateral margins; telson semicircular ( Figs. 1 View FIGURE 1 E, 2C). G1 relatively slender, distal pectinated part elongated, gently curved, expanded, spatuliform, tip medially clefted ( Fig. 2 View FIGURE 2 G–K).

Colour. Not known. Ecology. Not known.

Remarks. The species was described on the basis of two male and three female specimens collected probably from Sintang, along the Kapuas River in western Kalimantan, Borneo (De Man 1899: 133). Serène (1968a: 1089) identified a female specimen as the lectotype without discussion (see Fransen et al. 1997: 123).

The lectotype female is an adult; while the larger paralectotype male is mature, its chelae are still relatively small. Its male abdomen and G1, however, are fully formed. One characteristic feature of this species is that although the dorsal margin of the dactylus is mostly unarmed except for a few small granules on the proximal part ( Figs. 1 View FIGURE 1 F, 2F), there is a prominent transverse comb-like structure on the inner surface of the chela ( Fig. 2 View FIGURE 2 F).

Geosesarma amphinome View in CoL is superficially similar to G. sarawakense (Serène, 1968) View in CoL (from central Sarawak), G. peraccae (Nobili, 1903) View in CoL (from Singapore and southern Peninsular Malaysia), and G. pylaemenes View in CoL sp. nov. (from Anjungan, Kalimantan Barat), with similar trapezoidal carapace shapes and the exopod of their third maxillipeds possess a long flagellum ( Figs. 1 View FIGURE 1 A, B, 2A, B, 3A, B, 4A, 5A, B, 6A, B, 7A; Serène 1968a: pl. 1 fig. 3; Ng 1988: fig. 56A, C). Geosesarma amphinome View in CoL , G. peraccae View in CoL and G. pylaemenes View in CoL sp. nov. possess a prominent transverse comblike structure on the inner surface of the chela ( Figs. 2 View FIGURE 2 F, 3F, 5F; Ng 1988: fig. 56A). The chela of the holotype of G. sarawakense View in CoL is small (cf. Serène 1968a: pl. 1 fig. 3) but also has a low transverse ridge ( Fig. 6 View FIGURE 6 F).

Geosesarma amphinome View in CoL can be distinguished from G. sarawakense View in CoL by the dorsal surface of the anterior part of the carapace being more prominently granular ( Figs. 1 View FIGURE 1 A–C, 2A versus Fig. 6 View FIGURE 6 A–C; Serène 1968a: pl. 1 fig. 3), and the distal pectinated part of the G1 is more curved, spatuliform and relatively longer ( Fig. 2 View FIGURE 2 G–K) (the distal pectinated part of the G1 is straight and relatively shorter in G. sarawakense View in CoL , Fig. 7 View FIGURE 7 D–F; Serène 1968a: figs. 7, 8). The dorsal surface of the carapace, male abdomen and G1 of G. peraccae View in CoL is distinctly different from G. amphinome View in CoL , with the dorsal surface prominently more granular, somite 6 proportionately broader and the G1 being very slender, with the distal pectinated part almost straight ( Fig. 5 View FIGURE 5 A, B, D; Ng 1988: fig. 56D–F) (the carapace less granular, the abdominal somite 6 less broad, and the distal pectinated part wider and gently curved in G. amphinome View in CoL , Figs. 1 View FIGURE 1 A– D, 2C, G–K).

Although both G. amphinome View in CoL and G. pylaemenes View in CoL sp. nov. occur in Kalimantan Barat, their type localities (Sintang and Anjungan, respectively) are almost 200 km apart. Geosesarma amphinome View in CoL can be separated from G. pylaemenes View in CoL sp. nov. in having the anterior half of the dorsal surface of the carapace relatively more granular ( Fig. 1 View FIGURE 1 A–C versus Fig. 3 View FIGURE 3 A, B), the external orbital tooth is more acutely triangular ( Figs. 1 View FIGURE 1 A–C, 2A) (more broadly triangular in G. pylaemenes View in CoL sp. nov., Fig. 3 View FIGURE 3 A, B), abdominal somite 6 is proportionately less broad and the telson is not recessed into its distal margin ( Figs. 1 View FIGURE 1 E, 2C) (somite 6 broader and the telson is partially recessed into its distal margin in G. pylaemenes View in CoL sp. nov., Fig. 4 View FIGURE 4 B), and the G1 is relatively shorter with the distal pectinated part proportionately broader and more spatuliform, and with the median part deeply clefted ( Fig. 2 View FIGURE 2 G–K) (G1 relatively more slender with the distal pectinated part narrower and not strongly clefted medially in G. pylaemenes View in CoL sp. nov., Fig. 4 View FIGURE 4 D–G).

Geosesarma sarawakense View in CoL and G. peraccae View in CoL are both lowland species, typically associated with freshwater swamps or muddy forested habitats. Considering their similarity with G. amphinome View in CoL , the latter species probably lives in similar habitats. Geosesarma peraccae View in CoL has also been observed to forage in cups of pitcher plants (Nepentheceae) ( Tan & Ng 2008), and G. amphinome View in CoL may have similar phytotelmic habits. In any case, other species of Geosesarma View in CoL have been reported from this habitat: G. malayanum Ng & Lim View in CoL , in Ng, 1986, from Peninsular Malaysia (Ng & Lim 1987); G. nemesis Ng, 1986 View in CoL , from southern Peninsular Malaysia; G. b a u from Sarawak (see comparative material examined) and G. gracillimum View in CoL from Brunei (S. Choy, pers. comm.).

It is noteworthy that the holotype of G. sarawakense View in CoL was actually collected with another species of Geosesarma View in CoL . This specimen, an ovigerous female (11.2 × 10.9 mm) (ZRC 1965.7.29.5), has a quadrate carapace, longer ambulatory legs and is clearly a separate species. In the absence of a male, it is provisionally referred to G. bau View in CoL for the time being.