Parathelphusa nobilii, Ng, Peter K. L., 2014

Ng, Peter K. L., 2014, The identity of the Sarawak freshwater crab Parathelphusa oxygona Nobili, 1901, with description of a new species, Parathelphusa nobilii, from Western Kalimantan, Indonesia, Borneo (Crustacea: Brachyura: Gecarcinucidae), Zootaxa 3774 (1), pp. 31-44 : 41-43

publication ID	https://doi.org/ 10.11646/zootaxa.3774.1.2
publication LSID	lsid:zoobank.org:pub:9F68C81B-BBE9-4021-A742-D56CCDB16DCD
DOI	https://doi.org/10.5281/zenodo.6138768
persistent identifier	https://treatment.plazi.org/id/2B035F66-FF8B-2319-FF2E-714F5B6E3088
treatment provided by	Plazi
scientific name	Parathelphusa nobilii
status	sp. nov.

Treatment

Parathelphusa nobilii View in CoL sp. nov.

( Figs. 1 View FIGURE 1 B, C, 2B, D, F, 3B, D, F, H, J, 4F–J)

Telphusa (Paratelphusa) tridentata —von Martens 1868: 19 (part) (not Parathelphusa tridentata H. Milne Edwards, 1853 View in CoL ). Paratelphusa tridentata — Wood-Mason 1876: 121, 122 (part).

Potamon (Parathelphusa) oxygonus — Rathbun 1905: 239 (part) (not Parathelphusa maculata oxygona Nobili, 1901 View in CoL ). Parathelphusa oxygona View in CoL —Ng & Goh 1987: 317 (part).— Ng & Grinang 2004: 315 (part).

Material examined. Holotype— 1 male (38.5× 29.2 mm) ( ZRC 1989.3751), Sungai Nyuing-Sanggauledo- Sinkawang, Sambas District, Kalimantan, Indonesia, coll. F. Sabar & D. Hardjono, 6 September 1981. Paratypes— 1 female (40.5× 30.3 mm) ( ZRC 1989.3752), 2 males, 2 females ( MZB Cru 1247), same data as holotype.

Diagnosis. Carapace with branchial surfaces distinctly convex, appearing inflated from lateral view ( Fig. 2B View FIGURE 2. A, C, E ); external orbital tooth very broad, external margin slightly sinuous to almost straight, not separated into 2 parts ( Figs. 1 View FIGURE 1 B, C, 2F); postorbital cristae long, lateral parts ending abruptly just before base of first epibranchial tooth ( Figs. 1 View FIGURE 1 B, C, 2F); second epibranchial tooth separated from posterolateral margin gradually ( Fig. 1 View FIGURE 1 B, C); merus of ambulatory leg with distinct subdistal dorsal spine ( Figs. 1 View FIGURE 1 B, C, 3D); lateral margins of male abdominal somite 6 distinctly convex ( Fig. 3 View FIGURE 3. A, C, E, G, I H), male telson relatively long ( Fig. 3 View FIGURE 3. A, C, E, G, I H); G1 relatively slender, structure almost straight; proximal outer margin entire ( Fig. 4 View FIGURE 4. A – E F–I).

Description of male. Carapace hexagonal; transversely wider than long; dorsal carapace surface smooth; regions poorly demarcated; cervical groove broad, shallow; median H-shaped gastro-cardiac depression distinct. Frontal margin broad, not demarcated from supraorbital margin by notch or tooth, distinctly cristate, appearing sinuous from dorsal and frontal views; frontal median triangle distinct, very broad. Postfrontal cristae sharp, almost straight, separated from each other medially by narrow Y-shaped fissure; postorbital cristae long, sharp, gently sinuous, almost contiguous with postfrontal cristae, cristae ending somewhat abruptly just before reaching beginning of base of first epibranchial tooth. Branchial regions distinctly convex; appears gently inflated from lateral view. Orbits large, ovate; eyes well developed with prominent pigmented cornea, completely filling orbit. Supraorbital margin concave, entire; confluent with frontal margin; suborbital margin concave, entire. Pterygostomian region covered with scattered low granules; suborbital and subhepatic regions with low striae and granules. External orbital tooth very broadly triangular, external margin slightly sinuous but not separating tooth into 2 parts; inner angle acutely triangular, sharp, extending to level of frontal margin; outer part low, separated from first epibranchial tooth by broadly V-shaped notch; first epibranchial tooth sharp, triangular, directed anteriorly; second epibranchial tooth sharp, acutely triangular, directed obliquely outwards; separated from posterolateral margin gradually. Posterolateral margin gently sinuous, without visible crista, lateral surfaces with strong striae; posterolateral margin converging towards gently convex posterior carapace margin. Posterior margin of epistome sinuous; median tooth triangular with rounded tip, lateral margins convex.

Third maxilliped elongate, completely covering buccal cavity when closed; merus subquadrate, slightly wider than long, median part depressed, anterolateral margin subauriculiform, prominently rounded; ischium rectangular, with deep submedian oblique sulcus; exopod relatively stout, reaching to median part of merus, with distinct subterminal tooth on inner margin, flagellum long.

Chelipeds subequal in adult males; merus relatively short; with distinct subdistal spine; carpus ovate, outer surface distinctly rugose, with prominent, elongate spine on inner distal angle, inner margin gently serrated; chelae enlarged, outer surface smooth to gently rugose; fingers not pigmented black, gently curved, longer than palm, cutting edges with small and large rounded teeth and denticles. Ambulatory legs relatively short, stout; second leg longest; merus subrectangular, margins cristate, dorsal margin with sharp subdistal spine; carpus with cristate dorsal margin, unarmed; propodus with dorsal margin cristate, ventral margin gently serrated; outer surface with shallow submedian longitudinal depression; dactylus gently curved with corneous tip, quadrate in cross-section, margins with 4 rows of strong sharp spines.

Thoracic sternum evenly pitted, otherwise smooth; sternites 1, 2 completely fused, relatively narrow longitudinally; separated from sternite 3 by deep strongly concave suture (towards buccal cavity); sternites 3, 4 completely fused; sternoabdominal cavity reaching to imaginary line jointing anterior edges of coxae of chelipeds. Tubercle of press-button male abdominal locking mechanism rounded, on anterior edge of sternite 5.

Abdomen distinctly T-shaped; telson triangular, much longer than broad, lateral margins gently convex, tip rounded; somite 6 subrectangular, almost twice as long as broad, lateral margins convex; somites 3–5 trapezoidal; lateral margins of somites 4, 5 deeply concave; lateral margins of somite 3 very broad, gently convex; somites 1, 2 longitudinally narrow, wide, reaching to bases of coxae of last pair of ambulatory legs.

G1 relatively slender, terminal and subterminal segments not differentiated; entire structure almost straight, distal part straight, not curved; outer margin almost straight, entire, without indentation on proximal part; outer margin of subdistal margin with long setae; tip tapering to tip, opening distinct, laterally positioned. G2 much longer than G1; distal segment elongate, three-quarters length of basal segment.

Female. Chelae slender, not enlarged or inflated. Abdomen strongly ovate, covering almost entire surface of thoracic sternum; all somites and telson free; telson broadly triangular with gently convex lateral margins. Vulvae relatively large, posterior part with domed structure, anterior part with soft, semilunate operculum; on submedian part of thoracic sternite 6, slightly closer to suture between sternites 5, 6.

Colour in life. Not known.

Etymology. The species is named after Giuseppe Nobili of Turin, who made many valuable contributions to the carcinology of Borneo in the early 1900s.

Remarks. Von Martens (1868) identified specimens from Sinkawang, Borneo, as P. tridentata , which were later referred to P. oxygona by Nobili (1901). Rathbun (1905) and Ng & Grinangr (2004) also referred specimens they had from Sinkawang to P. oxygona , with Ng & Grinang (2004: 317) commenting that observed differences in the external orbital angle and gonopods may perhaps be explained by variation. A detailed re-examination of all the specimens on hand, especially the good series of P. oxygona , however, indicates that the Sinkawang material should be regarded as a distinct species, P. nobilii sp. nov.

Although von Martens (1868) did not describe the armature of the meri of the ambulatory legs, Wood-Mason (1876), who examined some of his specimens, observed that the merus has a sharp subterminal spine. Rathbun (1905: 239) identified a male specimen 36.0× 27.4 mm from Sinkawang in the Paris Museum as P. oxygona . The branchial regions of her Sinkawang specimen appear to be slightly swollen with the external orbital tooth broad and the posterior part not distinctly dentiform ( Rathbun 1905: pl. 11 fig. 6); and the lateral margins of the male abdominal somite 6 are convex ( Rathbun 1905: text fig. 57a); agreeing very well with the types of P. nobilii sp. nov. on hand.

As noted above, the present specimens from Sinkawang are distinctive in having the external orbital angle lower and wider ( Figs. 1 View FIGURE 1 B, C, 2F) and the G1 much straighter than those of P. oxygona , the outer margins being straight ( Fig. 4 View FIGURE 4. A – E F, G). The form of the external orbital angle does vary slightly, with the posterior part slightly angular in some specimens (e.g., see Fig. 1 View FIGURE 1 C; Rathbun 1905: pl. 11 fig. 6), and in this respect, somewhat resembling that of P. oxygona . However, the external orbital tooth of P. nobilii sp. nov. is always relatively wider and lower compared to P. oxygona ( Figs. 1 View FIGURE 1 B, C, 2F versus Figs. 1 View FIGURE 1 A, 2E). The branchial regions of P. nobilii sp.

nov. are always comparatively more convex ( Figs. 2B View FIGURE 2. A, C, E ) than those of P. oxygona ( Figs. 2A View FIGURE 2. A, C, E ), especially when viewed laterally, giving it a more inflated appearance. The male abdomen of P. nobilii sp. nov. is relatively more slender than of P. oxygona , mainly because the lateral margins of somite 6 are distinctly convex ( Fig. 3 View FIGURE 3. A, C, E, G, I H) (rather than gently convex in P. oxygona , Fig. 3 View FIGURE 3. A, C, E, G, I G), and the telson is proportionately longer ( Fig. 3 View FIGURE 3. A, C, E, G, I H) (rather than relatively shorter in P. oxygona , Fig. 3 View FIGURE 3. A, C, E, G, I G). The structure of the G1 is perhaps the most effective way of separating the two species, being consistently straighter and the proximal outer margins entire in P. nobilii sp. nov. ( Fig. 4 View FIGURE 4. A – E F–I) while in P. oxygona , the G1 is gently curved distally and the proximal outer margin is indented ( Figs. 4A–D View FIGURE 4. A – E , 5 View FIGURE 5. G 1 s ). These differences cannot be explained by the known variation for P. oxygona for which we have an excellent series of specimens. The G1 structures of the paratype males of P. nobilii sp. nov. are not as straight as those of the holotype, being very slightly curved but still less so that those of P. oxygona . Most significantly, the proximal outer margin of the G1 of P. nobilii sp. nov. does not have the distinct cleft ( Fig. 4 View FIGURE 4. A – E F, G) which is present in P. oxygona , even if sometimes it is small ( Figs. 4A, B View FIGURE 4. A – E , 5 View FIGURE 5. G 1 s ).

Sinkawang, the type locality of P. nobilii sp. nov. is some 130 km southwest of the Lundu area, the westernmost locality in Sarawak where P. oxygona is present. The area between these localities is covered by several mountain ranges that could easily have isolated the two lowland species.