Isolapotamon feeae, Ng & & Clark & Paul F., 2022

Ng, Peter K. L., , Martyn E. Y. Low, Clark, & Paul F., 2022, Historical notes on various collectors of unidentified freshwater crabs (Crustacea: Decapoda: Brachyura) from the Malay Peninsula and Borneo, with descriptions of two new species of Isolapotamon Bott, 1968 Potamidae), Raffles Bulletin of Zoology 70, pp. 550-571 : 556-560

Isolapotamon feeae , new species

( Figs. 2, 3, 6A–D)

Material examined. Sarawak, Borneo, Malaysia. Holotype: male (45.0 × 34.2 mm) ( NHM 1898.10.25.15), Baram River , coll. C. Hose. Paratypes : 1 male (36.2 × 25.9 mm), 3 females (49.3 × 36.7 mm, 44.3 × 34.2 mm, 38.2 × 28.7 mm) ( NHM 1898.10.25. 16), same data as holotype ; 1 juv. ( NHM 1895.7.2.34), Baram , coll. C. Hose, January 1895 .

Comparative material. Isolapotamon collinsi Holthuis, 1979: 2 males (larger 44.4 × 34.8 mm), 1 female ( ZRC 1997.0792 ), around Kuala Belalong Field Centre , Brunei, coll. S. Choy, 8–9 February 1991; 1 male, 3 juveniles ( ZRC 1997.0793 ), Temburong, Sungai Belalong , Kuala Belalong Field Centre, Brunei, coll. K. Lim et al., 14–17 June 1995 ; 6 males (largest 51.1 × 39.2 mm), 2 females ( ZRC 2008.0539 ), just downstream of Kuala Belalong Field Centre , Sungai Mata Ikan, Belalong Basin, Temburong district, Brunei, 4º32′50.4″N 115º09′27.6″E, coll. H. H. Tan, 6–9 October 2001 . Isolapotamon borneense Ng & SH Tan, 1998: 6 males, 4 juveniles ( ZRC 2022.0781 ), station THH02-33, Arur Dalan , Sungai Arur Dalan , Bario Plateau, Baram Basin, Sarawak, 03º45′32.1″N 115º26′28.0″E, Malaysia, 1110 m, coll. H. H. Tan & I. Das, 17 June 2002 .

Diagnosis. Carapace wider than long, relatively low, dorsal surface of carapace gently convex to almost flat; epigastric cristae sharp, just anterior of postorbital cristae; postorbital cristae sharp, subparallel to front; median lobe of posterior margin of epistome acutely triangular ( Fig. 2A–C). P2– P5 merus relatively long, dactylus of P5 long ( Figs. 2A, 3I). Press-button of male pleonal locking mechanism on submedian part of sternite 5 ( Fig. 3A). Male pleon subtriangular ( Fig. 2F, G). G1 sinuous; subterminal segment relatively long, with basal part broad, forming subrectangular structure, distal part slender; terminal segment strongly sinuous, curved, terminal segment strongly curved, sinuous, distal part relatively elongate, lobiform, curved about 90 ° from immediately preceding subdistal part, with distal margin distinctly sinuous, tip rounded ( Figs. 3D–G, 6A–C).

Females and variation. The smaller males of this species in which the gonopods are developed are almost identical to the holotype male, with the G1 structure agreeing in structure. The females agree with the males in all nonsexual characters except that their chelipeds are relatively more slender. The female pleon is ovate and covers most of the thoracic sternum and the telson is almost semicircular ( Fig. 3B). The vulvae are large, occupying more than half width of sternite 6, with the anterior margin pushing into the suture between sternites 5 and 6, and the posterior margin possessing a low ridge ( Fig. 3C).

Etymology. This new species is named for Félice “Fee” Vera Slade whose “enthusiasm, energy and keen eyesight during fieldwork” is recognised here (see information on collectors).

Remarks. Two Isolapotamon species are known from and around Baram; I. collinsi Holthuis, 1979 (from Gunung Mulu National Park and Brunei) and I. borneense Ng & SH Tan, 1998 (from upper Baram) (cf. Holthuis, 1979; Ng & SH Tan, 1998; Grinang et al., 2014). Isolapotamon borneense was described from an unknown site in Sarawak, but Grinang et al. (2014) confirmed that the species was from the Pulong Tai National Park area on the eastern drainage of the Baram River. The locality data for the new species, I. feeae , new species, is not detailed, but as it is a different species, it was likely to have been collected from the western catchment of the Baram River which drains from a different mountain range. More collections in that area will need to be made to confirm this supposition.

Not unexpectedly, the species closest to I. feeae , new species, is I. borneense , which occurs in the eastern drainage of Baram River (Grinang et al., 2014). The G1 of I. feeae , however, differs markedly from that of I. borneense in having the G1 subterminal segment proportionately longer, the terminal segment more strongly curved and sinuous, and the distal part of the terminal segment more elongate with the distal margin distinctly sinuous ( Figs. 3D–G, 6A–C) (cf. Ng & SH Tan, 1998: fig. 1M–P; Grinang et al., 2014: figs. 3A–D, E, G–I, J, L–M). Noteworthy is that the carapace of I. feeae is distinctly wider proportionately; Fig. 2A, B (vs. carapace more quadrate in I. borneense ; Grinang et al., 2014: fig. 2A–C), and the P2–P5 meri are distinctly longer; Fig. 4I (vs. meri are distinctly shorter in I. borneense ; Grinang et al., 2014: fig. 2F).

One small juvenile specimen (NHM 1895.7.2.34) from Baram is referred to this species only because it was collected from the type locality.