Geosesarma danumense Ng, 2002

Ng, Peter K. L. & Ng, Paul Y. C., 2018, The freshwater crabs of Danum Valley Conservation Area in Sabah, East Malaysia, with a description of a new species of Thelphusula Bott, 1969 (Crustacea, Brachyura, Gecarcinucidae, Potamidae, Sesarmidae), ZooKeys 760, pp. 89-112 : 89

Geosesarma danumense Ng, 2002 Figure 7 A–C

Geosesarma danumense Ng, 2002: 303, figs 1-3; Ng et al. 2008: 220.

Material examined.

Holotype: male (14.8 × 14.6 mm) (ZRC 2017.1298), in pitfall trap, primary forest, Danum Valley Field Centre, Sabah, Malaysia, coll. C. Colón, 22 November 1996. Others: 1 ovigerous female (14.9 × 15. mm) (ZRC 2017.1273), in water filled rotting log, Nature Trail, Danum Valley Field Centre, Sabah, Borneo, coll. local rangers, 21 July 2017.

Comparative material.

Geosesarma sabanum Ng, 1992: holotype male (13.1 × 13.6 mm) (ZRC 2018.0296), on leaf of herb in forest, ca. 50 m from nearest stream, Tawau Hills Park, eastern Sabah, Malaysia, Borneo, coll. R.F. Inger, 3 November 1991.

Colour.

Geosesarma danumense has a dark yellow to orange carapace, purple ambulatory legs with scattered white specks, orange merus and carpus of the chelipeds, with the palm and fingers white (Fig. 7 A–C). The eggs of the recently collected ovigerous female were observed to be a bright reddish orange in colour and large in size, indicating that the development is probably direct (see Soh 1969; Ng and Tan 1995). The live coloration is very similar to the related G. sabanum Ng, 1992 from Tawau (Fig. 7D).

Remarks.

Geosesarma danumense and G. sabanum are morphologically close, although the external orbital tooth of the latter species is proportionately more slender, the frontal margin less truncate, the ambulatory meri proportionately shorter, and most significantly the corneous distal part of the G1 is proportionately longer (see Ng 2002).

The holotype of G. danumense was obtained from a pitfall trap while the recent large ovigerous female (ZRC 2017.1273) was collected from under a rotting log. Specimens have also been observed climbing small shrubs. In this respect, it probably has similar habits to G. sabanum from Tawau which has been observed by the second author to hide between the leaves of Pandanus sp. during the day, emerging only at night to forage on low lying vegetation and occasionally amongst leaf litter (unpublished data). The terrestrial habits of G. danumense and G. sabanum probably parallel those known for species in Peninsular Malaysia and Indonesian Kalimantan ( Ng 2015, 2017).

Manuel-Santos et al. (2016: 336) commented that the three species of Geosesarma on Palawan Island in the Philippines, G. lawrencei Manuel-Santos & Yeo, 2007, G. batak Manuel-Santos, Ng & Freitag, 2016, and G. tagbanuana Manuel-Santos, Ng & Freitag, 2016, are morphologically very similar to the Sabahan G. danumense and G. sabanum , notably in their relative large adult size and long slender ambulatory legs. Their G1 structures, however, are very different, with those of the latter two species proportionately much shorter and stouter (cf. Ng 1992, 2002; Manuel-Santos and Yeo 2007; Manuel-Santos et al. 2016).