Arachnothelphusa Ng, 1991

Ng, Peter K. L., 2021, On two new species of arboreal crabs from phytotelms in Sarawak, Borneo (Crustacea: Brachyura: Gecarcinucidae: Arachnothelphusa), Zootaxa 5016 (3), pp. 407-418 : 408

Arachnothelphusa Ng, 1991

Type species. Potamon (Potamon) melanippe De Man, 1899 , by original designation.

Remarks. Bott (1970) treated Potamon (Geothelphusa) kadamaianum Borradaile, 1900 , as a subspecies of Potamon (Potamon) melanippe De Man, 1899 , placing both in Thelphusula Bott, 1969 . Ng (1991) redefined the genus, establishing Arachnothelphusa for these two species because of their long ambulatory legs as well as their distinctive G1 and G2 structures. Of the known species of Arachnothelphusa , A. terrapes is probably the most atypical, with the external orbital tooth separated from the epibranchial tooth by a deep U-shaped sinus with the entire frontal region sunken in, the G1 terminal segment prominently curves upwards and the G2 distal segment is very short ( Ng 1991; Ng & Ng 2018). All other congeners have a more normal carapace with the frontal margin level with the anterolateral margin, the G1 terminal segment is conical and straight, and the G2 distal segment is longer.

On the basis of the height of the carapace, A. melanippe , A. kadamaiana , A. merarapensis and A. rhadamanthysi as well as the new species here, A. bako n. sp., belong to one group where it is high and the structure looks more inflated (e.g., Figs. 7C , 9C ). Arachnothelphusa terrapes and A. rimba n. sp. belong to the second group where the carapace is not as high and the structure appears less inflated (e.g., Fig. 1C ). The difference, however, does not appear to be a phylogenetic one as the character cannot be correlated with the male pleonal and gonopodal features, and is probably associated with the habits and habitat of individual species. The proportions of the ambulatory legs is a useful character but should only be used between specimens of the same sex. As noted by Grinang et al. (2015), female specimens of A. merarapensis generally have relatively longer ambulatory legs than males. This same condition is observed in A. kadamaiana ; with the male P2–P5 relatively shorter (e.g., length to width ratio of P4 merus 4.34–4.36; Fig. 10F, G ) whereas in females, the P4 merus length to width ratio is 5.45 ( Fig. 10E ).

Comparative material. Arachnothelphusa melanippe (De Man, 1899) : Lectotype male (18.9 × 14.4 mm) ( NNM D1303 a), Liang Koeboeng Mountains (= present day Liang Kubung), Kalimantan, Indonesia, coll. C Büttikofer, 1897 ; paralectotype female (21.4 × 16.7 mm) ( NNM D1303 b), same data as lectotype. Arachnothelphusa kadamaiana ( Borradaile, 1900) : Holotype female (18.9 × 13.5 mm) ( SMF 4281 ), Kadamian River , Sabah, East Malaysia, Borneo ; 1 male (20.1 × 14.9 mm) ( SMF 4282 ), same locality as holotype ; 1 female (23.2 × 17.1 mm) ( ZRC 2009.0094 ), Poring , Basin 1A, Sabah, Malaysia, 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 ), Crocker Range , Sabah, 5º27’N 116º03’E, coll. I. Das, 24 April 2001 . Arachnothelphusa rhadamanthysi ( Ng & Goh, 1987) : holotype female (16.9 × 12.0 mm) ( ZRC 1990.0443 ), Simud Puteh Cave , Gomantong , Sabah, East Malaysia, Borneo, 5°33’N 118°06’E, coll. P. Chapman, 25 March 1986 . Arachnothelphusa terrapes Ng, 1991 : Holotype male (17.6 × 13.3 mm) ( ZRC 1992.7918 ), Danum Valley Field Centre , station 507, in dry stump on ridge, Lahad Datu, Sabah, Borneo, coll. H.K. Voris, 23 October 1990 ; paratype female (25.7 × 18.6 mm) ( ZRC 1992.7919 ), Danum Valley , Lahad Datu, Sabah, Borneo, coll. S.C. Choy, 21 July 1989 ; 1 male (30.8 × 20.5 mm), 1 female (30.1 × 20.5 mm, with 26 juvenile crabs) ( ZRC 2017.1205 ), from water-filled tree buttress, ca. 35 cm above ground Danum Valley , Lahad Datu, Sabah, Borneo, Malaysia, coll. 20 July 2017 . 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, 4º22’25.4”N 115º26’10.1”E, 485 m asl, coll. J. Grinang & Y.M. Pui, 31 October 2014 . Arachnothelphusa sarang Grinang & Ng, 2021 : Holotype male (20.4 × 14.7 mm) ( ZRC 2020.0098 ), 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 ), 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 ), 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 ), limestone cave, Batu Kelelut , Bukit Sarang, Bintulu, Sarawak, Malaysia, coll. H.H. Tan et al., 18 August 2005 .

Figures

FIG. 7. Arachnothelphusa bako n. sp., holotype female (19.0 × 14.2 mm) (ZRC 2002.0098), Bako. A, overall dorsal view; B, dorsal view of carapace; C, frontal view of cephalothorax; D, left third maxilliped; E, third maxillipeds, anterior thoracic sternum and pleon; F, posterior margin of epistome; G, outer view of right chela.

FIG. 9. Arachnothelphusa kadamaiana (Borradaile, 1900), holotype female (18.9 × 13.5 mm) (SMF 4281), Kadamian River.A, overall dorsal view; B, dorsal view of carapace; C, frontal view of cephalothorax; D, left third maxilliped; E, third maxillipeds, anterior thoracic sternum and pleon; F, posterior margin of epistome; G, outer view of right chela.

FIG. 1. Arachnothelphusa rimba n. sp., holotype male (22.8 × 16.6 mm) (ZRC 2020.0366), Lanjak-Entimau. A, overall dorsal view; B, dorsal view of carapace; C, frontal view of cephalothorax; D, left third maxilliped; E, anterior thoracic sternum and pleon; F, pleon; G, outer view of right chela; H, outer view of left chela.

FIG. 10. Ambulatory legs. A–D, Arachnothelphusa bako n. sp., holotype female (19.0 × 14.2 mm) (ZRC 2002.0098), Bako; E, A. kadamaiana (Borradaile, 1900), holotype female (18.9 × 13.5 mm) (SMF 4281), Kadamian River; F, A. kadamaiana (Borradaile, 1900), male (21.1 × 15.8 mm) (ZRC 2002.0097), Crocker Range; G, A. kadamaiana (Borradaile, 1900), male (22.8 × 16.5 mm) (ZRC 2002.0097), Crocker Range. A, left P4; B, left P5 merus; C, E–G, right P4; D, right P5.