Isolapotamon buntyae, 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 : 560

Isolapotamon buntyae , new species

( Figs. 4, 5, 6E–H)

Material examined. Holotype: male (43.6 × 32.7 mm) ( NHM 2022.170 ), “Ulu Dusun, North Borneo”, Sabah, Malaysia, coll. J. Kidman-Cox, 1 August 1972, presented by Reptile Section.

Diagnosis. Carapace wider than long, relatively high, dorsal surface of carapace convex; epigastric cristae rugose, not sharp, anterior of postorbital cristae; postorbital cristae sharp, sloping posteriorly from front; median lobe of posterior margin of epistome acutely triangular ( Fig. 4A–C). P2–P5 merus relatively long, dactylus of P5 long. Press-button of male pleonal locking mechanism on median part of sternite 5 ( Fig. 5A). Male pleon distinctly triangular ( Fig. 5F, G). G1 gently sinuous; subterminal segment relatively long, with basal part broad, forming subrectangular structure, distal part slender; terminal segment strongly sinuous, curved, distal part bifurcated, subdistal projection as long as distal projection, lobiform with rounded tip, laterally flattened ( Figs. 5B–E, 6E–G). Female unknown.

Females and variation. Only known from the holotype male.

Etymology. The species is named after Alice Georgie Cruickshank “Bunty” Grandison, a well-respected, pioneering female herpetologist and museum curator (see information on collectors).

Remarks. The bifurcated distal part of the G1 of I. buntyae , new species, is diagnostic and places this species in a group with four other species sharing this character: I. griswoldi (Mount Kinabalu, Sabah), I. collinsi (Gunung Mulu and Brunei), I. nimboni (southern and central Sarawak), and I. grusophallus (southern Sarawak). Although Ng & SH Tan (1998) recognised I. stuebingi Ng, 1995b , as a distinct species, it has been subsequently shown that the holotype is just a subadult specimen of I. nimboni and the two names are now regarded as synonyms (cf. Ng, 2004: 324; Ng et al., 2008: 163).

The G1 subdistal process of I. grusophallus is the most distinctive, being prominently elongate and more than twice the length of the distal part (cf. Ng & Yang, 1986: fig. 1H–K; Ng, 1987b: fig. 3G, H; Ng & SH Tan, 1998: fig. 6A–D; Grinang et al., 2014: fig. 5A, B, D, E, H–K, M–P, R–T). The G1 of I. griswoldi is the shortest proportionately among all the members of this group of species, with the subdistal process short and almost rounded in appearance ( Chace, 1938: pl. 1f–h; Bott, 1969: fig. 2; Bott, 1970: pl. 41, fig. 78; Ng & SH Tan, 1998: fig. 5M–P). The general features of the G1 of I. buntyae most closely resemble those of I. collinsi and I. nimboni . Compared to I. buntyae , the G1 terminal article of I. collinsi is gently sinuous and the subdistal process is subcylindrical in shape and distinctly longer than the distal process and positioned at a right angle with respect to the main stem of the terminal article ( Fig. 7D, E, F, G, I, J, K, L; Holthuis, 1979: fig. 4b; Ng, 1987b: fig. 3F; Ng & SH Tan, 1998: fig. 5A–D (vs. terminal article strongly sinuous with the subdistal process laterally flattened and slightly longer than the distal process in I. buntyae ; Figs. 5B–E, 6E–G). In I. nimboni , the G1 terminal segment is similar to that of I. collinsi , being gently sinuous to almost straight but the subdistal process is conical in shape, subequal to the distal process in length and positioned at a more acute angle ( Ng, 1987b: fig. 2H–J; Ng & SH Tan, 1998: fig. 10I–L).

Ng & Goh (1987: 328, pl. 3C, D) reported a female specimen from near Gomantong in eastern Sabah which could not be identified to the species level. This site is some 42 km to the southeast of Ulu Dusun. From the general appearance of the carapace (notably the relatively flatter carapace) and the broader median lobe on the posterior margin of the epistome, however, it is unlikely that the Gomantong specimen is conspecific with I. buntyae .