Arachnothelphusa, Ng, 1991

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 : 6

Key to species of Arachnothelphusa of Borneo

1. Epibranchial tooth very low or indistinct; external orbital tooth very low, broad; anterolateral region less rugose, fine granules, carapace surface smooth ( Figs. 1C, F , 2A, B, C, F, G , 4A ); G1 gently curving outwards, terminal segment about one-third length of subterminal segment; distal segment of G2 less than a quarter length of basal segment ( Fig. 3A–E )........................ ........................... A. sarang , new species (northern Sarawak)

– Epibranchial tooth distinct, triangular; external orbital tooth triangular; anterolateral region prominently rugose, coarse granules, carapace surface rugose ( Fig. 4B–E ); G1 gently or strongly curving outwards, terminal segment either half, onethird or a quarter length of subterminal segment; distal segment of G2 either a quarter or one-fifth length of basal segment ( Fig. 5 )..............................................................................................2

2. Epibranchial tooth distinct, acutely triangular; G1 strongly curving outwards ( Fig. 5F, H, O, Q )......................................3

– Epibranchial tooth distinct, relatively blunt; G1 gently curving outwards ( Fig. 5A, C, K )........................................................4

3. Epibranchial tooth acutely triangular, distinctly separated from external orbital tooth by wide, deep cleft; external orbital acutely triangular ( Fig. 4B ); terminal segment of G1 about half of length of subterminal segment; distal segment of G2 about quarter length of basal segment ( Fig. 5A–E )................. ...................................... A. merarapensis (northern Sarawak)

– Epibranchial tooth distinct but relatively small, separated from external orbital tooth by small cleft; external orbital tooth broadly triangular ( Fig. 4E ); terminal segment of G1 about one-third of length of subterminal segment; distal segment less than a quarter length of basal segment ( Fig. 5O–S )......... ......................................... A. melanippe (central Kalimantan)

4. Epibranchial tooth distinct; external orbital tooth broadly triangular ( Fig. 4D ); terminal segment of G1 about a third length of subterminal segment ( Fig. 5K–M )............................ ............................................ A. kadamaiana (northern Sabah)

– Epibranchial tooth distinct; external orbital tooth triangular; terminal segment of G1 about a quarter length of subterminal segment....................................................................................5

5. Epibranchial tooth distinct on both sides, separated from external orbital tooth by deep, broad U-shaped cleft; external orbital tooth triangular ( Fig. 4C ); G1 with cone-shaped terminal segment, about a quarter length of subterminal; distal segment of G2 less than fifth length of basal segment ( Fig. 5F–J )....... ..................................................... A. terrapes (eastern Sabah)

– Epibranchial tooth distinct on both sides, small, blunt, not separated from external orbital tooth by cleft.......................... .......................................... A. rhadamanthysi (eastern Sabah)

Figures

Fig. 1. Arachnothelphusa sarang, new species. A, male (12.1 × 9.9 mm) (ZRC 2020.0351), Batu Rusa cave, Bukit Sarang, Bintulu, Sarawak, Malaysia; B, female (12.9 × 10.4 mm) (ZRC 2020.0351), Batu Kelelut, Bukit Sarang, Bintulu, Sarawak, Malaysia, specimen; C–E, paratype male (18.7 × 15.3 mm) (ZRC 2020.0099), Bukit Sarang, Bintulu, Sarawak, Malaysia; F, paratype female (15.8 × 11.8 mm) (ZRC 2020.0099), Bukit Sarang, Bintulu, Sarawak, Malaysia. A, B, photographed in situ; C, F, overall dorsal habitus; D, ventral view of cephalothorax; E, frontal view of cephalothorax and chelae. Photographs: Tan Heok Hui.

Fig. 2. Arachnothelphusa sarang, new species. A–E, holotype male (20.4 × 14.7 mm) (ZRC 2020.0098), Bukit Sarang, Bintulu, Sarawak, Malaysia; F, G, paratype female (19.8 × 15.8 mm) (ZRC 2020.0100), Bukit Sarang, Bintulu, Sarawak, Malaysia. A, F, dorsal view of habitus; B, G, ventral view of carapace showing pleon; C, frontal view of cephalothorax; D, outer view of left chela; E, outer view of right fourth ambulatory leg. Scales: A, B, C, F, G = 10 mm; D, E = 5 mm.

Fig. 4. Carapace morphology of Arachnothelphusa species. A, A. sarang, new species, holotype male (20.4 × 14.7 mm) (ZRC 2020.0098), limestone cave, Bukit Sarang, Bintulu, Sarawak; B, A. merarapensis Grinang, Pui & Ng, 2015, holotype male (22.5 × 16.8 mm) (ZRC 2016.0297), Merarap Hot Spring, Lawas, Sarawak; C, A. terrapes Ng, 1991, male (30.8 × 20.5 mm) (ZRC 2017.1205), Danum Valley, Lahad Datu, Sabah; D, A. kadamaiana (Borradaile, 1900), male (20.1 × 14.9 mm) (SMF 4282), Kadamian River, Sabah; E, A. melanippe (De Man, 1899), paratype female (21.4 × 16.7 mm) (RMNH D1303b), Mt. Liang Koebeng, Kalimantan, Indonesia. E after Ng (1991).

Fig. 3. Arachnothelphusa sarang, new species, holotype male (20.4 × 14.7 mm) (ZRC 2020.0098), limestone cave, Bukit Sarang, Bintulu, Sarawak, Malaysia. A, dorsal view of left G1; B, dorsal view of distal part of left G1; C, ventral view of left G1; D, ventral view of distal part of left G1; E, dorsal view of left G2. Scales = 0.5 mm.

Fig. 5. Gonopod morphology of Arachnothelphusa species. A–E, A. merarapensis Grinang, Pui & Ng, 2015, holotype, male (22.5 × 16.8 mm) (ZRC 2016.0297), Merarap Hot Spring, Lawas, Sarawak; F–J, A. terrapes Ng, 1991, holotype, male (17.6 × 13.3 mm) (ZRC 1992.7918), Danum Valley, Lahad Datu, Sabah; K–N, A. kadamaiana (Borradaile, 1900), male (20.1 × 14.9 mm) (SMF 4282), Kadamian River, Sabah; O–S, A. melanippe (De Man, 1899), lectotype, male (18.9 × 14.4 mm) (RMNH D1303a), Mt. Liang Koebeng, Kalimantan, Borneo. C, F, K, O, ventral view of left G1; D, G, L, P, ventral view of distal part of left G1; A, H, Q, dorsal view of left G1; B, I, M, R, ventral view of distal part of left G1; E, J, N, S, left G2. A–E, K–N after Grinang et al. (2015); F–J, O–S after Ng (1991).