Thelphusula cristicervix ( Ng & Grinang, 2004 ) Grinang & Ng, 2014

Grinang, Jongkar & Ng, Peter K. L., 2014, Taxonomy of the freshwater crab Coccusa cristicervix Ng & Grinang, 2004 (Decapoda: Brachyura: Gecarcinucidae), with description of a new species of Thelphusula from Sarawak, Malaysia, Borneo, Raffles Bulletin of Zoology 62, pp. 389-395 : 390

Thelphusula cristicervix ( Ng & Grinang, 2004) , new combination

( Figs. 1 , 3A–E , 4 )

Coccusa cristicervix Ng & Grinang, 2004 : fig. 5; Ng, 2004: 321; Ng & Yeo, 2007: 9; Ng et al., 2008: 69; Cumberlidge et al., 2009: Appendix 1.

Material examined. Holotype: female (19.9 × 14.3 mm) (SBC.C.00130), Gunung Doya , limestone outcrop, Bau District , Sarawak, coll. A. Denis et al., 2 October 2002. Others : 2 males (20.0 × 14.8 mm, 21.8 × 16.6 mm) ( SBC), Sama Jaya Nature Reserve, lowland heath swamp forest, 16 m above sea level, Kuching Division, Sarawak, coll. J. Grinang et al., 3 July 2013; 4 males (15.1–19.4 mm × 11.3–14.8 mm), 4 females (19.1–24.8 mm × 14.6–18.7 mm) ( ZRC), Sama Jaya Nature Reserve, lowland heath swamp forest, 16 m above sea level, Kuching Division, Sarawak, coll. P.K.L. Ng et al., 13 September 2013.

Diagnosis. Carapace gently ovate; cervical groove deep, prominent, with distinct rows of cristae running along length; postorbital cristae low, rounded, not sharp, separated from low, rounded epigastric cristae low by shallow depressions; anterolateral margin entire, epibranchial teeth not discernible; H-shaped depression relatively shallow ( Fig. 1A, B ). Frontal margin deflexed; frontal median triangle not clearly discernible, area marked by depression ( Fig. 1C ). Median tooth on posterior margin of epistome subtruncate ( Fig. 1C ). Ambulatory legs relatively long ( Fig. 1A ). Major chela stout, with gap at base of closed fingers ( Fig. 1G ). Male abdomen with somite 6 elongate, lateral margins gently concave ( Fig. 1D ). G1 terminal segment subconical, tip sharply tapering, about 2 times length of subterminal segment ( Fig. 3A, C–E ). G2 with distal segment very short, tip sharp ( Fig. 3B ).

Colour. In life, the species is red to bright red overall all the dorsal surfaces and pereopods (adult male chelae usually more orangish-red), with the ventral surfaces yellowish-white ( Fig. 4A, B ).

Remarks. The recent series of specimens of T. cristicervix from Sama Jaya Nature Reserve just outside Kuching city is about 40 km from the type locality in Bau, but agree extremely well with the holotype specimen in all aspects; including the structure of the carapace and proportions of the ambulatory legs. The good series, which includes small and large specimens, leaves little doubt to their conspecificity.

The morphology of the G1 of this species agrees well with what has been diagnosed and figured for Thelphusula Bott, 1969 , by Tan & Ng (1998), with the terminal segment slender, cylindrical and distinctly shorter than the subterminal segment ( Fig. 3A, C ). The carapace shape, as well as granulation of T. cristicervix , while relatively more ovate than other known species of Thelphusula which have more quadrate ones, approaches the condition in more species like T. dicerophilus and T. granosa which have relatively more inflated carapaces (cf. Holthuis, 1979: pl. 5; Ng & Stuebing, 1990: pl. 1).

In contrast to the moist karst forest where the holotype of T. cristicervix was collected, the recent specimens were all collected from a swampy part of a well-shaded kerangas forest. The soil is wet and loamy, usually with a dense root system permeating it. The crabs dig relatively deep burrows, up to perhaps a metre in depth in places and come out only at night. The presence of the species in both limestone and kerangas forests indicates that its distribution is delimited by soil conditions rather than forest type.

Ng & Yeo (2007: 9) noted that the species was endangered, commenting that “the Bau area [type locality] does not have long-term protection and the species occurs in low-lying areas, it is very vulnerable to anthropogenic and associated effects.” (see also Cumberlidge et al., 2009: Appendix 1). The discovery of T. cristicervix in a nature reserve near Kuching city does not change its status as the protected area is open to the public and the species is known mainly from one small patch of swamp only several hundred square metres in area.

Figures

Fig. 1. Thelphusula cristicervix (Ng & Grinang, 2004). Male (19.4 × 14.8 mm) (ZRC), Sama Jaya Nature Reserve, Kuching Division, Sarawak. A, overall dorsal view; B, dorsal view of carapace; C, frontal view of carapace; D, ventral view showing anterior thoracic sternum and male abdomen; E, left third maxilliped; F, outer view of right chela; G, outer view of left chela.

Fig. 3. A–E, Thelphusula cristicervix (Ng & Grinang, 2004), male (19.4 × 14.8 mm) (ZRC), Sama Jaya Nature Reserve, Kuching Division, Sarawak; F–J, Thelphusula pueh, new species, male (16.2 × 12.1 mm) (ZRC), Kampung Sebako, Pueh, Lundu District, Sarawak. A, F, ventral view of left G1; B, G, ventral view of left G2; C, H, dorsal view of left G1; D, I, ventral view of terminal segment of left G1; E, J, dorsal view of terminal segment of left G1. Scale bars: A–C, F–H = 1.0 mm; D, E, I, J = 0.5 mm.

Fig. 4. Colours in life, Thelphusula cristicervix (Ng & Grinang, 2004). A, male (ca. 19.0 mm carapace width), in situ in forest, specimen not collected; B, female (19.3 × 14.2 mm) (ZRC) [Photograph by: Tan HH]. Both specimens from Sama Jaya Nature Reserve, Kuching Division, Sarawak.