Terrathelphusa secula, Ng, Peter K. L. & Tan, Leo W. H., 2015

Ng, Peter K. L. & Tan, Leo W. H., 2015, Terrathelphusa secula, a new species of semiterrestrial freshwater crab (Crustacea: Brachyura: Gecarcinucidae) from Sabah, East Malaysia, Borneo, Zootaxa 4007 (3), pp. 445-449 : 447-449

publication ID	https://doi.org/ 10.11646/zootaxa.4007.3.13
publication LSID	lsid:zoobank.org:pub:33503B98-5979-44C4-B231-8BDE7E0A6AC5
DOI	https://doi.org/10.5281/zenodo.6116217
persistent identifier	https://treatment.plazi.org/id/03F69305-FFA9-FFE6-FF2D-466FFD34FDFE
treatment provided by	Plazi
scientific name	Terrathelphusa secula
status	sp. nov.

Treatment

Terrathelphusa secula View in CoL , new species

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Material examined. Holotype: male (29.2 × 20.4 mm) ( ZRC), found dead in pool adjacent to Borneo Rainforest Lodge, next to Danum Valley Conservation Area, Lahad Datu, Sabah, 458.2’N 11741.4’E, ca. 600 m asl, East Malaysia, Borneo, coll. local ranger, 28 May 2015.

Diagnosis. Carapace transversely ovate, distinctly wider than long, width to length ratio 1.43 ( Fig. 1 View FIGURE 1 A, B). Cephalothorax prominently swollen; dorsal surface distinctly convex, median parts smooth, branchial surfaces with distinct oblique striae; cervical grooves deep; epigastric cristae low, barely visible, separated by shallow longitudinal groove; postorbital cristae not visible; H-groove distinct, almost confluent with cervical grooves; epibranchial tooth undiscernible, external orbital angle, anterolateral margin separated by very low depression, margin otherwise unarmed, appearing almost entire; anterolateral, frontal regions appearing somewhat compressed; supraorbital margin subparallel with broadly bilobed front, median part of frontal margin bent downwards but no median triangle visible ( Fig. 1 View FIGURE 1 A, B). Epistome with median lobe broad, rounded ( Fig. 1 View FIGURE 1 C). Ischium of third maxilliped rectangular, ca. 1.6 times maximum width ( Fig. 1 View FIGURE 1 D). Cheliped carpus distinctly rugose ( Fig. 1 View FIGURE 1 A), inner angle with sharp tooth, with basal sharp tubercle; fingers slightly shorter than palm, gap between fingers of major chela wide ( Fig. 2 View FIGURE 2 D). Ambulatory legs smooth, relatively slender, second pair longest; length of fourth merus ca. 4.1 times maximum width ( Fig. 2 View FIGURE 2 F, G). Male abdomen with linguiform telson, somite 6 elongated with deeply concave lateral margins ( Fig. 2 View FIGURE 2 A–C). G1 slender, C-shaped, curving outwards; terminal segment elongated, falciform, tapering gradually to subtruncate tip, ca. 0.5 times length of subterminal segment, surfaces with long, short stiff setae, distalmost surfaces with small scale-like spines ( Fig. 3 View FIGURE 3 A–E). G2 with distal segment short, ca. 0.3 times length of basal segment ( Fig. 3 View FIGURE 3 F).

Life colour. The carapace was dark brown in the recently dead specimen.

Habitat. The specimen was found freshly dead in a small pool near a lodge by a local ranger. Like other Terrathelphusa species, T. secula n. sp. almost certainly digs deep burrows in the soil, coming out to forage only at night ( Collins 1979; Grinang & Ng 2015). Three other species of freshwater crabs are known from the Danum Valley Conservation Area: Thelphusula dicerophilus Ng & Stuebing, 1990 (Gecarcinucidae) , Isolapotamon ingeri Ng & Tan, 1998 (Potamidae) , and Geosesarma danumense Ng, 2002 (Sesarmidae) (see Ng 2002; Ng & Stuebing 1990; Ng & Tan 1998).

Etymology. The name is derived from the Latin secula for sickle; alluding to the strongly curved G1 structure of this species. The name is used as a noun in apposition.

Remarks. Terrathelphusa secula n. sp. belongs to the group of Terrathelphusa species that have relatively low epigastric cristae, a third maxilliped ischium that is relatively short (length to width ratio 1.5–1.6), and a relatively short G2 distal segment (0.5 times or less then the length of the basal segment). The two other species belonging to this group, T. ovis and T. telur are from eastern Sarawak and Borneo. All the other Terrathelphusa species have more prominent epigastric cristae, a relatively longer third maxilliped ischium (length to width ratio 1.8–2.1 times) and a much longer G2 distal segment (0.6 length of basal segment or longer) ( Grinang & Ng 2015: Table 1). The carapace shape of T. secula n. sp., however, is much wider and more transversely ovate than those of T. ovis and T. telur , and is most similar to the condition observed for T. loxophthalma (cf. Ng 1997: fig. 3). It is certainly more tranversely ovate and proportionately wider than any of the species now known from western Sarawak (cf. Grinang & Ng 2015).

The most diagnostic feature of T. secula n. sp. is its distinctive sickle-shaped G1. While other species of Terrathelphusa can have gently curved G1s (e.g., T. ovis and T. telur , cf. Ng 1997: figs. 6E–H, J–L, 8C–F), none have a G1 that is as strongly curved and with a terminal segment that long ( Fig. 3 View FIGURE 3 A, B, D). In fact, the length of the G1 terminal segment of T. secula n. sp. is such that it closely resembles those of several species of the gecarcinucid genus Thelphusula Bott, 1969 (cf. Tan & Ng 1998; Grinang & Ng 2014). The carapace of Thelphusula species is nevertheless more quadrate, the epigastric and postorbital cristae are distinct, the male abdomens is relatively broader, and the distal segment of the G2 is very short (see Tan & Ng 1998).