Arachnothelphusa sarang, Grinang & Ng, 2021

Grinang, Jongkar & Ng, Peter K. L., 2021, A new species of the genus Arachnothelphusa Ng, 1991 (Crustacea: Decapoda: Gecarcinucidae) from a limestone cave in Sarawak (Malaysian Borneo), Raffles Bulletin of Zoology 69, pp. 1-7 : 1-6

publication ID	https://doi.org/ 10.26107/RBZ-2021-0001
publication LSID	lsid:zoobank.org:pub:F861B9E5-475A-4A3D-B2AC-B49646FA7CC9
persistent identifier	https://treatment.plazi.org/id/03D25556-FFA5-3131-FC2C-FA6BFD48DCCA
treatment provided by	Diego
scientific name	Arachnothelphusa sarang
status	sp. nov.

Treatment

Arachnothelphusa sarang View in CoL , new species

( Figs. 1A–F View Fig , 2A–G View Fig , 3A–E View Fig , 4A View Fig )

Material examined. Holotype: male (20.4 × 14.7 mm) ( ZRC 2020.0098 View Materials ), limestone cave, Bukit Sarang, Bintulu , Sarawak, Malaysia, coll. H.H. Tan et al., 20 August 2005 . Paratypes: 1 male (18.7 × 14.8 mm), 4 females (15.8–19.8 × 12.0– 15.8 mm) ( ZRC 2020.0099 View Materials ), same data as holotype ; 10 males (7.4–11.2 × 5.8–9.6 mm), 7 females (7.5–12.7 × 5.8–9.9 mm) ( ZRC 2020.0100 View Materials ), limestone cave, Batu Gelam , Bukit Sarang, Bintulu , Sarawak, Malaysia, coll. H.H. Tan, 20 August 2005 ; 1 male (12.1 × 9.9 mm), 1 female (12.9 × 10.4 mm) ( ZRC 2020.0351 View Materials ), limestone cave, Batu Kelelut , Bukit Sarang, Bintulu , Sarawak, Malaysia, coll. H.H. Tan et al., 18 August 2005 .

Comparative material. Arachnothelphusa merarapensis Grinang, Pui & Ng, 2015 : Holotype male (22.5 × 16.8 mm) (ZRC 2016.0297), water-filled tree-hole, ca. 100

cm above ground, steep dipterocarp forest, Merarap Hot Spring Resort, Lawas, northern Sarawak, Malaysia, Borneo , 4°22′25.4″N 115°26′10.1″E, 485 m asl, coll. J. Grinang & Y.M. Pui, 31 October 2014; paratype GoogleMaps female (19.9 × 15.2 mm) (SBC.C.00376), water-filled hole of tree buttress, ca. 90 cm above ground, steep dipterocarp forest, Merarap Hot Spring Resort, Lawas, northern Sarawak, Malaysia, Borneo , 4°22′16.5″N 115°26′12.4″E, 494 m asl, coll. J. Grinang & Y.M. Pui, 1 November 2014 GoogleMaps ; 1 female (22.3 × 16.1 mm) (SBC.C.00377), water-filled hole of tree buttress, ca. 30 cm above ground, same data as paratype, coll. Y.M. Pui, 27 February 2013. Arachnothelphusa kadamaiana ( Borradaile, 1900) : Holotype GoogleMaps female (18.9 × 13.5 mm) ( SMF 4281 About SMF ), Kadamian River , Sabah, Malaysia, Borneo ; 1 male (20.1 × 14.9 mm) ( SMF 4282 About SMF ), same data as holotype ; 1 female (23.2 × 17.1 mm) ( ZRC 2009.0094 View Materials ), Poring, Basin 1A, Sabah, Borneo , coll. R.F. Inger et al., 12 August 1992 ; 3 males (21.1 × 15.8 mm, 22.8 × 16.5 mm, 25.3 × 18.5 mm) ( ZRC 2002.0097 View Materials ), Crocker Range , Sabah, 5°27′N 116°03′E, coll. I. Das, 24 April 2001. Arachnothelphusa aff. kadamaiana GoogleMaps : 1 female (19.0 × 14.2 mm) ( ZRC 2002.0098 View Materials ), Bako National Park , Sarawak, coll. I. Das & L. Grismer, 27 March 2001. Arachnothelphusa terrapes Ng, 1991 : Holotype male (17.6 × 13.3 mm) ( ZRC 1992.7918 View Materials ), Danum Valley Field Centre, station 507, in dry stump on ridge, Lahad Datu, Sabah, Borneo , leg. H.K. Voris, 23 October 1990; paratype female (25.7 × 18.6 mm) ( ZRC 1992.7919 View Materials ), Danum Valley, Lahad Datu, Sabah, Borneo , leg. S.C. Choy, 21 July 1989; others : 1 male (30.8 × 20.5 mm), 1 female (30.1 × 20.5 mm, with 26 juvenile crabs) ( ZRC 2017.1205 View Materials ), from water-filled tree buttress, ca. 35 cm above ground Danum Valley, Lahad Datu, Sabah, Borneo , Malaysia, 20 July 2017. Arachnothelphusa melanippe (De Man, 1899) : Lectotype male (18.9 × 14.4 mm) ( RMNH D1303 About RMNH a), Liang Koebeng Mountains , Kalimantan, leg. 1897; paralectotype female (21.4 × 16.7 mm) ( RMNH D1303 About RMNH b), same as lectotype .

Diagnosis. Carapace surface convex, rugose, finely granular; anterolateral margins convex, serrated; antero- and posterolateral regions prominently rugose, covered with numerous coarse granules; epibranchial tooth very low or indistinct; external orbital tooth very low, broadly triangular, outer margin slightly concave, distinctly serrated; epigastric and postorbital cristae distinct; cervical and H-grooves deep, not confluent ( Fig. 2A, C View Fig ); ambulatory legs long, merus of fourth ambulatory legs subequal to length of carapace ( Fig. 2A, B, E View Fig ); carpus of chelipeds rugose, with fine granules, inner angle with broadly triangular tooth ( Fig. 2A, D View Fig ); chela relatively short, fingers as long as palm, cutting teeth on pollex not prominent ( Fig. 2D View Fig ). Male pleon T-shaped, somite 6 subequal to length of telson ( Fig. 2B View Fig ). G1 slender, sinuous, gently curving outwards; terminal segment cylindrical, tapering, about one third length of subterminal segment ( Fig. 3A–D View Fig ). G2 with short distal segment, less than a quarter length of basal segment ( Fig. 3E View Fig ).

Females. The females differ in minor non-sexual characters by the carapace being slightly broader and lower ( Fig. 2F, G View Fig ). Female pleon broad, round, somite 6 subequal to length of telson, tip of telson round pointed ( Fig. 2G View Fig ). In larger specimens of both sexes, the antero- and posterolateral regions have relatively more coarse granules. The vulvae are transversely ovate, large, without obvious sternal vulvar covers and are positioned on the median part thoracic of sternite 6.

Variation. The numerous paratype specimens agree well with the holotype male in non-sexual characters.

Colour. In life, the species is pale purplish brown to yellowish in both sexes on the dorsal surfaces, the ventral surfaces being pale yellow to dirty white. The corneas of the eyes are large and fully pigmented ( Fig. 1 View Fig ).

Etymology. The species is named after the locality where the holotype was collected. The name is used as a noun in apposition.

Remarks. Arachnothelphusa sarang , new species, is easily distinguished from A. merarapensis , A. terrapes , A. melanippe , and A. rhadamanthysi by its very low to indistinct epibranchial tooth as well as the very low, broad external orbital tooth ( Figs. 1C, F View Fig , 2A–C, F, G View Fig , 4A View Fig ). In A. merarapensis , the epibranchial tooth is acutely triangular, separated from the external orbital tooth by a wide and deep cleft and the external orbital tooth is acutely triangular ( Fig. 4B View Fig ; cf. Grinang et al., 2015: fig. 1A–C). In A. terrapes , the epibranchial tooth is distinct on both sides, separated from the external orbital tooth by a deep and broad U-shaped cleft and the external orbital tooth is triangular ( Fig. 4C View Fig ; cf. Ng, 1991: fig. 3 [incorrectly printed as fig. 5]; cf. Ng & Ng, 2018: fig. 5B–F). In A. melanippe , the epibranchial tooth is distinct but relatively small and separated from the external orbital tooth by a small cleft, with the external orbital tooth broadly triangular ( Fig. 4E View Fig ; cf. De Man, 1899: pl. 9 fig. 11; Ng, 1991: fig. 1). In A. rhadamanthysi , the epibranchial tooth is distinct on both sides with the external orbital tooth triangular (cf. Ng & Goh, 1987: pl. 3A, B). In carapace features, A. sarang is perhaps closest to A. kadamaiana , but they can be distinguished by the presence of a distinct epibranchial tooth and a relatively more anteriorly projecting and acute apex of the external orbital tooth for the latter ( Figs. 2A–C, F, G View Fig , 4A View Fig versus Fig. 4D View Fig ; cf. Grinang et al., 2015: fig. 6A). The anterolateral region of A. sarang is distinctly less rugose with fine granules, whereas this region is prominently rugose with coarse granules for congeners ( Fig. 4A View Fig versus 4B–E). The structure of the G1 of A. sarang differs from that of A. terrapes and A. melanippe in gently curving outwards ( Fig. 3A–D View Fig ) versus distinctly curving outwards in the latter two species ( Fig. 5F–I, O–R View Fig ). In the G1 structure, A. sarang is similar to A. merarapensis and A. kadamaiana , but they can be distinguished by the following features: the terminal segment of the G1 of A. sarang and A. kadamaiana is about one-third the length of the subterminal segment ( Figs. 3A–D View Fig , 5K–M View Fig ); while that of A. merarapensis is about half the length of the subterminal segment ( Fig. 5A–D View Fig ). The distal segment of the G2 of A. sarang and A. merarapensis is less than a quarter the length of the basal segment ( Figs. 3E View Fig , 5E View Fig ), but in A. kadamaiana , it is less than one-fifth the length of the basal segment ( Fig. 4N View Fig ). The gonopods of A. rhadamanthysi are not known.

The live colouration of the two cave species differs markedly from those of the epigeal species. The live colouration of A. sarang , new species, ranges from light purplish to yellowish brown ( Fig. 1 View Fig ). This is similar to that known for the other cavernicolous species, A. rhadamanthysi , which is pale straw-yellow with white legs ( Fig. 6 View Fig ; cf. Ng & Goh, 1987: 326). Arachnothelphusa merarapensis is bright purple overall (cf. Grinang et al., 2015: fig. 3A, B), whereas A. terrapes is brown to reddish-brown (cf. Ng, 1991: figs. 4, 5 [not labelled in original paper]; Ng & Ng, 2018: fig. 5B–E). The habits and live colouration of A. melanippe and A. kadamaiana are not known.

The habitat, pale colouration in life, and general appearance of Arachnothelphusa sarang , new species, are also similar to those of the genus Stygothelphusa Ng, 1989 , which contains four species, all from limestone caves in Sarawak ( Ng, 1991, 2013; Ng & Grinang, 2014). The carapace of Stygothelphusa , however, is generally more quadrate (versus more transversely ovate in Arachnothelphusa ), the ambulatory legs are proportionately even longer, and most significantly, the G2 is much longer than the G1, with the distal segment long and flagelliform (versus G2 shorter than G1, with the distal segment short in Arachnothelphusa ). hill surrounded by peat swamp, comprises a complex of small caves with different names, most of which are almost certainly with subterranean interconnections, and is part of the Tatau River basin. All the specimens of A. sarang were found in water pools with fine substrates, and co-existing with whelk snails, several hundred metres from the cave entrance; none were observed near the cave mouth (H. H. Tan, pers. comm.). The limestone cave of Bukit Sarang is a protected area and important for sustainable edible birdnest production. The harvesting of bird-nests will have to be done carefully so as not to pollute or disturb the habitat if the crab is to be conserved.

Members of Arachnothelphusa occur in a wide variety of habitats ranging from tree-holes to caves. The only other species of Arachnothelphusa known from caves is A. rhadamanthysi . Arachnothelphusa sarang inhabits exclusively deep interior of cave systems of Bukit Sarang in northern Sarawak. Arachnothelphusa rhadamanthysi on the other hand, has been found in more exposed areas near the cave entrance of Gomantong limestone cave in western Sabah ( Fig. 6 View Fig ). Both species, however, are not troglobitic species as neither have their eyes reduced and the corneas are still completely pigmented, and A. rhadamanthysi at least has been found at cave entrances. In this respect, the habits of the two species are the same as species of Stygothelphusa , which are regarded as troglophilic taxa instead ( Ng, 1991, 2013; Ng & Grinang, 2014). Another cavernicolous gecarcinucid from Borneo, Balssiathelphusa phasma Ng & Guinot, 2014 , from eastern Kalimantan in Indonesia, is also regarded as troglophilic ( Ng & Guinot, 2014). As such, the only true stygobitic crabs in Borneo are the two species of Cerberusa Holthuis, 1979 , from northern Sarawak (family Potamidae ) ( Holthuis, 1979) and the monotypic Guaplax Naruse, Ng & Guinot, 2008 , from southern Kalimantan (family Hymenosomatidae ) ( Naruse et al., 2008).