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| 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. |
Abstract
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
TAXONOMY
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.
RAFFLES BULLETIN OF ZOOLOGY. 63: 454–460
RAFFLES BULLETIN OF ZOOLOGY. 63: 454–460
