Research Article |
Corresponding author: Peter K. L. Ng ( peterng@nus.edu.sg ) Academic editor: Sammy De Grave
© 2017 Peter K. L. Ng.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Ng PKL (2017) Salangathelphusa peractio, a new species of lowland freshwater crab (Crustacea, Brachyura, Gecarcinucidae) from Pulau Langkawi, Peninsular Malaysia. ZooKeys 711: 53-65. https://doi.org/10.3897/zookeys.711.20621
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A new species of lowland freshwater crab of the family Gecarcinucidae, Salangathelphusa peractio, is described from Langkawi, an island off the northwestern coast of peninsular Malaysia. Salangathelphusa peractio sp. n. can be separated from S. brevicarinata (Hilgendorf, 1882) in having a proportionately broader external orbital tooth, a distinctly concave posterolateral margin, and the terminal segment of the male first gonopod is not distinctly bent laterally outwards; and from S. anophrys (Kemp, 1923) by its more quadrate carapace and the terminal segment of the male first gonopod possessing a relatively longer and less curved distal part. This is sixth wholly freshwater brachyuran species known from the island.
Gecarcinucidae , Langkawi Island, Malaysia, new species, Salangathelphusa , taxonomy
The gecarcinucid genus Salangathelphusa was established by
Salangathelphusa can easily be distinguished from all other southeast Asian gecarcinucids by possessing the following combination of characters: four teeth on its anterolateral margin (including the external orbital tooth); a dorsal carapace surface which is smooth with the postorbital cristae barely visible or absent; a male first gonopod which is very short and stout, with the terminal and subterminal segments clearly demarcated and a short terminal segment which has the basal part dilated and the distal part sharply tapering; and the male second gonopod has a long distal segment which is longer than half the length of the basal segment (
In 2015, the author examined old collections collected from the northwestern peninsular Malaysian island of Langkawi that had been collected during an expedition there by the Malayan Nature Society in 2003 (see
Specimens examined are deposited in the Zoological Reference Collection (ZRC) of the Lee Kong Chian Natural History Museum, National University of Singapore; and the Zoological Survey of India (ex Indian Museum), Calcutta, India. Measurements, in millimetres, are of the maximum carapace width and length, respectively; while the abbreviations G1 and G2 are used for the male first and second gonopods, respectively. The terminology used follows that in
Parathelphusa salangensis Ortmann, 1893, by original designation.
Holotype: male (22.3 × 17.7 mm) (ZRC 2017.208), Sungai Batu Asah, Kuah, Langkawi, Kedah, 6°20'22.13"N, 99°48'33.55"E, Peninsular Malaysia, coll. A. Ahmad et al., University of Sains Malaysia expedition to Langkawi, 11 April 2003. Paratypes: 1 young male (12.0 × 10.6 mm) (ZRC 2017.209), same data as holotype; 10 males (largest 22.4 × 17.7 mm, 21.9 × 17.3 mm), 2 juvenile males, 1 female (largest 21.7 × 17.3 mm), 5 young females (largest 15.3 × 13.0 mm) (ZRC 2017.210), small sandy shaded stream with rocks, 4–5 cm depth, adjacent to main river, downstream with dense waterweeds, Lubuk Semilang Park, south of Gunung Raya mountain, Langkawi, Kedah, 6°21'49.2"N, 99°47'29.39"E, Peninsular Malaysia, coll. P. K. L. Ng, 14–15 July 2017.
Salangathelphusa brevicarinata (Hilgendorf, 1882): 25 males (largest 25.5 × 20.6 mm), 7 females (ZRC), Nam Tok Tone Sai, 08°01.64'N 98°21.74'E, Phuket, Thailand, coll. P. K. L. Ng and H. H. Tan, 8 April 1999; 2 males (larger 25.8 × 21.2 mm) (ZRC), same locality as above, coll. P. K. L. Ng, December 1999; 3 males, 2 females, 2 juveniles (ZRC), same locality as above, coll. S. S. C. Chong, 3 April 1985; 4 males (largest 24.7 × 19.9 mm), 2 females (ZRC), Nam Tok Kathun, 07°55.96'N, 98°19.43'E, Phuket, Thailand, coll. P. K. L. Ng and H. H. Tan, 8 April 1999. Salangathelphusa anophrys (Kemp, 1923): holotype male (25.4 × 19.0 mm) (ZSI C 603/1), Khao Ram, 366 m asl, Nakhon Si Thammarat mountains, Peninsular Siam (= southern Thailand), coll. M. Smith, no date; 1 male (26.9 × 20.7 mm) (ZRC 1989.2011), Sai Rung waterfall, Trang Province, southern Thailand, coll. P. Naiyanetr, 27 October 1988.
Carapace subquadrate, broader than long (Fig.
Salangathelphusa peractio sp. n., holotype male (22.3 × 17.7 mm) (ZRC 2017.208), Langkawi. A left G1 (ventral view) B left G1 (dorsal view) C distal part of left G1 (ventral view) D distal part of left G1 (mesial view) E distal part of left G1 (dorsal view) F left G2. Scale bars A, B, F 1.0 mm C–E 0.5 mm.
of adult male. Carapace subquadrate, broader than long, adult carapace width to length ratio 1.25–1.27; dorsal surface gently convex, glabrous; regions poorly defined, cervical grooves shallow but, distinct, H-shaped gastrocardiac groove well developed (Fig.
Mandibular palp 2-segmented, terminal segment prominently bilobed. Third maxilliped with ischium rectangular, with distinct longitudinal submedian sulcus; merus squarish, anterolateral margin convex, not prominently auriculiform; exopod slender, reaching to midpoint of merus, with long flagellum (Fig.
Chelipeds subequal, outer surface of merus, carpus and palm rugose; palm of right chela slightly larger; fingers not gaping, longer than palm, tips gently hooked, cutting edges without molariform teeth; merus short, stout, surface rugose with distinct subdistal tubercle on dorsal margin; carpus with strong, obliquely directed subdistal spine on inner margin; merus with low subterminal spine (Figs
Ambulatory legs relatively short, stout, almost glabrous, surfaces gently rugose; second and third legs longest; merus not elongate, dorsal margin gently carinate, uneven, appearing serrated, ventral margins carinate, dorsal subdistal spine or tooth short but distinct; dactylus short, with short, sharp spines on margins (Fig.
Suture between anterior thoracic sternites 2 and 3 laterally interrupted, just visible as shallow transverse groove; sternite 3 distinctly compressed, longitudinally narrow, separated from sternite 4 by shallow lateral grooves; suture between sternites 4 and 5 medially interrupted; sutures between sternites 5/6, 6/7 and 7/8 complete with distinct median longitudinal groove on sternites 6 and 7; sternopleonal cavity extending beyond imaginary line joining anterior edge of cheliped bases, reaching to sternite 3 (Fig.
Pleon distinctly T-shaped, all somites and telson free; telson tongue-shaped, subequal to somite 6, lateral margins gently concave, tip broadly rounded; somite 6 subquadrate, lateral margins gently sinuous, distal margin slightly shorter than proximal margin; somites 3–5 trapezoidal (Fig.
G1 relatively short, stout; subterminal segment proportionately stout, gradually tapering towards distal half, outer margin gently sinuous; terminal segment less than half length of subterminal segment, outer margin convex, rounded tip directed upwards towards buccal cavity, inner basal part swollen, much wider than distal half, entire structure gently twisted towards sternal surface (Fig.
Adult females closely resemble adult males except that the chelae are relatively more slender. The adult female pleon is ovate and covers most of the thoracic sternum (Fig.
Salangathelphusa peractio sp. n. A, B paratype male (12.0 × 10.6 mm) (ZRC 2017.209), Langkawi C, D paratype female (21.7 × 17.3 mm) (ZRC 2017.210), Langkawi. A, C overall habitus B male anterior thoracic sternum and pleon D female anterior thoracic sternum and pleon E female sternopleonal cavity showing vulvae.
Smaller specimens (ca. 15 mm carapace width and below) have relatively more quadrate carapaces (width to length ratio 1.13–1.17), the merus of the ambulatory leg has a small dorsal subdistal spine and the male pleonal somite 6 is proportionately more trapezoidal in shape (Fig.
In life, Salangathelphusa peractio sp. n. is light brown to orange on all its dorsal surfaces; the dorsal surface of the carapace has large reddish-brown spots and markings at or near the cervical and gastro-cardiac grooves; and the chelipeds and ambulatory legs have numerous small reddish-brown spots (Fig.
The species name is derived from the Latin word “peractio” which means “ending of a story”. It alludes to the discovery of the present freshwater species, arguably the last one the author will describe from Langkawi, ending his 30-year history with the island. Gender feminine.
Salangathelphusa peractio sp. n. can easily be separated from S. brevicarinata in that its external orbital tooth is proportionately broader (Fig.
Salangathelphusa peractio is known thus far only from southern streams at the base of Gunung Raya, the highest peak on Langkawi. Its distribution appears to be localised, being confined to shallow streams with fast flowing water, the substrate of the stream bed and banks being rocks of various sizes. The gecarcinucid Siamthelphusa improvisa was sometimes found together with Salangathelphusa peractio, but the former species prefers areas with dense underwater vegetation and larger rocks. At Lubuk Semilang Park, Salangathelphusa peractio was found only in a small area a few hundred square metres, although there are several other similar areas with similar habitats which were not accessible. The park is not a protected area and is used by the public for all manner of recreational activities which partially pollute the area as well as causing substantial disturbance to the overall habitat. How these impacts affect the crabs is not known. Unfortunately, the species is not found in any fully protected site. The restricted distribution and potential habitat impacts means that the species should perhaps be regarded as vulnerable under current conservation guidelines (see
Thanks are due to Amir Ahmad for first passing material of Salangathelphusa to the author 14 years ago. The author is also grateful to Darren Yeo for sharing his unpublished photographs and notes of the type material of S. anophrys; and to him and Neil Cumberlidge for their helpful comments on the manuscript. Thanks are also due to Oliver Coleman for his hospitality during the author’s visit to examine types in the Berlin Museum in 2015.