Friday, October 16, 2015

[Crustacea • 2015] Arachnothelphusa merarapensis • A New Species of Tree-Hole Dwelling Freshwater Crab of the Genus Arachnothelphusa Ng, 1991 (Decapoda: Brachyura: Gecarcinucidae) from northern Sarawak, Malaysia, Borneo

Arachnothelphusa merarapensis  Grinang, Min & Ng, 2015
Fig. 3. The colour in life of Arachnothelphusa merarapensis, new species,
holotype male (22.5 × 16.8 mm) (ZRC), A, dorsal view; B, frontal view.
Fig. 4. Illustration of Arachnothelphusa merarapensis, new species, holotype male, emerging at night from its filled-water tree-hole in primary dipterocarp forest,
Merarap Hot Spring, Lawas, Sarawak.

A new species of tree-hole gecarcinucid freshwater crab, Arachnothelphusa merarapensis, is described from a primary dipterocarp forest near Merarap Hot Spring Resort in Lawas, northern Sarawak, Malaysia. This brings the number of species in the genus Arachnothelphusa found in Borneo to five, and it is likely that more species will be discovered from this island. The new species has preference for living in water-filled tree-holes, which is the first record of a tree-hole crab for Southeast Asia. The habitat characteristics and distribution of this new species are also discussed.

Key words. Brachyura, Gecarcinucidae, Arachnothelphusa, tree-hole, Sarawak, Borneo


Family Gecarcinucidae Rathbun, 1904

Arachnothelphusa merarapensis, new species

Etymology. The species is named after Merarap, the type locality where it was collected.

 Habitat. The habitat of A. merarapensis is a steep primary dipterocarp forest with a closed canopy, near the thermal springs area of the Merarap Hot Spring Resort. The holotype male was caught from a water-filled tree-hole, ca. 22 cm deep, ca. 15 cm in diameter, and ca. 100 cm above ground (Fig. 4). The bottom layer of the tree-hole consists of finely decomposed organic material (plant and arthropod debris), with the other two-thirds filled with water which increases after heavy rain. The two other specimens were caught from the water-filled crevices of tree buttresses. One buttress-crevice had a diameter of about 26 cm, was 60 cm deep, and 90 cm above the ground, and contained tightly compacted roots and leaf litter, with a hole dug into this that was apparently constructed by the crab. The other buttress-crevice runs along the side of the buttress and is about 30 cm above ground, shallow (15 cm), horizontal, and 30 cm deep. For two consecutive nights, the first two authors examined more than 15 tree-holes and crevices of different form, size, and conditions (either water-filled, dry, or debris-filled tree-holes), but we were only able to locate three specimens. This species is nocturnal and highly sensitive to light. We did not find any burrows on the soil around the tree-holes, suggesting the crab is a tree-hole specialist.

Other true freshwater crabs from the Old World showing similar phytotelmic behaviour are Potamonautes raybouldi Cumberlidge & Vannini, 2004 (Potamonautidae) in Tanzania, East Africa; Globonautes macropus (Rathbun, 1898) (Potamonautidae) in Liberia, West Africa; Malagasya goodmani (Cumberlidge, Boyko & Harvey, 2002) (Potamonautidae) in Madagascar; and Perbrinckia scansor (Ng, 1995) (Gecarcinucidae) in Sri Lanka (Ng, 1995; Cumberlidge & Sachs, 1991; Bayliss, 2002; Cumberlidge et al., 2002, 2005; Cumberlidge & Vannini, 2004; Bahir et al., 2008). In Sarawak, the sesarmid crab Scandarma splendidum has been reported climbing forest trees at night in western Sarawak (Naruse & Ng, 2007), but it is not known to be a phytotelm crab.

Conservation status. Considering unique habitat and probable limited distribution, A. merarapensis will easily be threatened by human activities, especially logging. The type locality is not protected but the forest is currently safe because it is part of the Merarap Hot Spring Resort. However, the forest in the vicinity is part of a concession allocated to logging companies and the future of the species is therefore uncertain. As such, we recommend that A. merarapensis should at least be listed as “Vulnerable” in the IUCN Red List of Threatened Species (cf. Cumberlidge et al., 2009).

Jongkar Grinang, Pui Yong Min and Peter K. L. Ng. 2015. A New Species of Tree-Hole Dwelling Freshwater Crab of the Genus Arachnothelphusa Ng, 1991 (Crustacea: Decapoda: Brachyura: Gecarcinucidae) from northern Sarawak, Malaysia, Borneo.