Parathelphusa oxygona Nobili, 1901

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 : 33-41

Parathelphusa oxygona Nobili, 1901

( Figs. 1 A, 2A, C, E, 3A, C, E, G, I, 4A–E, 5)

Potamon (Parathelphusa) tridentatum var. incertum — Lanchester 1900b: 255, pl. 12 fig. 2.—Hanitsch 1900: 9 (part) (not Potamon (Parathelphusa) tridentatum var. incertum Lanchester, 1900a ).

Parathelphusa maculata oxygona Nobili, 1901: 9 .

Potamon (Parathelphusa) oxygonus — Rathbun 1905: 239 (part).

Parathelphusa (Parathelphusa) maculata — Colosi 1920: 23 (part) (not Paratelphusa maculata De Man, 1879 ).

Parathelphusa (Parathelphusa) incerta — Bott 1970: 118 (part).

Paratelphusa (Paratelphusa) maculatus — Yang 1979: 16 (part).

Potamon maculata oxygona — Leh 1982: 4.

Parathelphusa maculata oxygona — Leh 1982: 6.

Parathelphusa oxygona —Ng & Goh 1987: 317 (part).—Ng 1988: 96; Ng 1990a: 54.— Ng 1990b: 245.—Ng 1993: 191.— Ng 2004: 330, fig. 13C.— Ng & Grinang 2004: 315 (part).—Ng & Yeo 2007: 113.— Cumberlidge et al. 2009: unpaginated appendix.— Klaus et al. 2013: 68.

Material examined. Lectotype (here designated)—1 crushed specimen ( MUT Cr 1211 Ex 1347), Sadong River, Sarawak, don. R. Shelford, 1900 (det. as Parathelphusa (Parathelphusa) maculata by Colosi 1920). Others: 2 males (larger 32.2× 24.9 mm), 2 females ( ZRC 1986.7512–7515), 1 male, 1 female ( MBA 981c), Sadong River (det. as Palawanthelphusa pulcherrima by R. Bott), ca. 1°55'N 113°08'E, coll. 1901; 1 male (34.0×30.0 mm) (SM Cru 1986.115); 1 female (SM Cru 1986.78), Simunjan, Upper Sadong, 1°22'N, 110°44'E, coll. Loong Tak, 18 June 1901; 2 males (42.0× 33.4 mm, 41.9×32.0 mm), 1 female (43.0× 32.6 mm) (SM Cru 1986.5–7), Bidi (= Bau Caves), 1°23'N, 110°6'E, coll. C.J. Brooks, June 1903; 5 males (largest 32.2× 24.9 mm, 31.4× 24.8 mm), 4 females ( ZRC 1989.2248, ZRC 1989.2239-2246), lowland stream, base of Gunong Serapi (Gunong Matang), near Kuching, 1°33.3'N 110°12.9'E, coll. P.K.L. Ng & M. Nimbon, 29 January 1986; 1 female ( ZRC 1989.3401), Sungei Rayu, Kuala Sendok, Matang, relatively fast flowing water, about 20 cm deep, ca. 30m asl, 1°36.8'N 110°9.4'E, coll. S. Yussof, 1988; 7 males (largest 36.6×28.0 mm), 5 females ( ZRC 1992.10546–10557), Serian, near Kuching, coll. P.K.L. Ng, July 1992; 2 females ( ZRC 1996.1942), 1°36.0'N 110°41.3'E, coll. H.H. Tan et al., 4 September 1995; 1 female ( ZRC 1996.1941), Sungai Sebiris, 1°41.5'N 109°47.0'E, coll. H.H. Tan et al., 1 September 1996; 2 males, 1 female ( ZRC 1996.1943), Sungai Belit, 1°3'N 110°45'E, coll. M. Kottelat et al., 2 July 1992; 6 males, 3 females ( ZRC 1996.1944), Red Bridge, at Matang, near Bau, 1°36.5'N 110°18.4'E, coll. H.H. Tan et al., 30 August 1996; 1 female ( ZRC 1996.1945), Lundu area, 1°46.6'N 109°44.7'E, coll. H.H. Tan et al., 6 September 1995; 2 females ( ZRC 1996.1948), Bau to Lundu road, 1°29.3'N 110°2.7'E, coll. H.H. Tan et al., 6 September 1995; 1 female ( ZRC 1996.1949), Bau to Lundu road, 1°39.0'N 110°41.0'E, coll. H.H. Tan et al., 4 September 1995; 5 males, 6 females ( ZRC 1996.1950), Lundu area, Bau to Lundu road, 1°48.1'N 109°43.7'E, coll. H.H. Tan et al., 1 September 1996; 1 female ( ZRC 1996.1951), Lundu area, 1°45.1'N 109°45.9'E, coll. coll. H.H. Tan et al., 1 September 1996; 2 males, 1 female ( ZRC 1996.1952), Bau-Lundu area, 1°22.9'N 110°7.1'E, coll. H.H. Tan et al., 7 September 1995; 6 males, 1 female ( ZRC 1996.1953), stream near Sungai Tengah, ca. 12.6 km into turn-off towards Singal, from Bau to Lundu road, 1°32.6'N 110°12.8'E, coll. H.H. Tan et al., 2 September 1996; 1 female ( ZRC 1996.1945), Sungai Stumm Muda, near Lundu, 1°28.9'N 109°58.3'E, coll. H.H. Tan et al., 2 September 1995; 1 female, 18 juveniles ( ZRC 1998. 547), Sungai Stumm Muda, before Lundu, 1°28.9'N 109°58.3'E, coll. students, 25 June 1998; 1 male, 1 female (39.4× 30.1 mm) ( ZRC 2008.1327), Sungai Stumm Muda, before Lundu, 1°28.9'N 109°58.3'E, coll. H.H. Tan et al., 6 September 1995; 1 male ( ZRC 1998.548), stream, Fairy Cave, 1°22.8'N 110°6.9'E, coll. students, 24 June 1998; 1 juvenile ( ZRC 1998.549), stream, Fairy Cave, Bau Caves, 1°22.8'N 110°6.9'E, coll. students, 24 June 1998; 1 female with 71 young ( ZRC 1999.687), Sungai Petiak, Kampung Blimbin, on road to Krokong, 1°21.3'N 110°6.8'E, pH 8.5, coll. H.H. Tan et al., 11 June 1999. All localities in western Sarawak, Borneo, East Malaysia.

Diagnosis. Carapace with branchial surfaces gently convex, not appearing inflated from lateral view ( Fig. 2A ); external orbital tooth very broad, external margin very sinuous to concave, approximately separating structure into 2 parts ( Figs. 1 A, 2E); postorbital cristae long, lateral parts gently curving posteriorly near base of first epibranchial tooth ( Figs. 1 A, 2E); second epibranchial tooth separated from posterolateral margin by broad angle ( Fig. 1 A); merus of ambulatory leg with distinct subdistal dorsal spine ( Figs. 1 A, 3C); lateral margins of male abdominal somite 6 gently convex ( Fig. 3 G), male telson relatively shorter ( Fig. 3 G); G1 relatively slender, distal part gently curving away from sternoabdominal cavity; proximal outer margin with distinct indentation ( Figs. 4A–D , 5 ).

Description of male. Carapace hexagonal; transversely wider than long; dorsal carapace surface smooth; regions poorly demarcated; cervical groove very broad, shallow; median H-shaped gastro-cardiac depression deep. Frontal margin broad, not demarcated from supraorbital margin by notch or tooth, distinctly cristate, appearing gently concave from dorsal, frontal views; frontal median triangle distinct, very broad. Postfrontal cristae sharp, gently concave to almost straight, separated medially other by narrow Y-shaped fissure; postorbital cristae long, sharp, gently concave to almost straight, separated from postfrontal cristae by small notch, cristae gently curving posteriorly as it reaches near base of first epibranchial tooth. Branchial regions gently convex; not distinctly inflated from frontal or 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. Pterygostomial region covered with scattered low granules; suborbital and subhepatic regions with low striae, granules. External orbital tooth very broad, vaguely separated into 2 parts by distinctly sinuous to concave external margin; inner angle acutely triangular, sharp, extending to level of frontal margin; outer angle obtusely triangular, rounded; separated from first epibranchial tooth by broad U-shaped notch; first epibranchial tooth sharp, triangular with subangular outer margin, directed anteriorly; second epibranchial tooth sharp, acutely triangular, directed obliquely outwards; separated from posterolateral margin by broad angle. Posterolateral margin gently concave, marked by low but distinct crista, lateral surfaces with distinct striae; posterolateral margin converging towards gently convex posterior carapace margin. Posterior margin of epistome sinuous; median tooth triangular with rounded tip, lateral margins concave.

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 stout, reaching to median part of merus, with distinct subterminal tooth on inner margin, flagellum long.

Chelipeds subequal in adult male; merus relatively short; with distinct subdistal spine; carpus ovate, outer surface 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, large rounded teeth, 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, narrow longitudinally; separated from sternite 3 by deep concave suture (towards buccal cavity); sternites 3, 4 completely fused; sternoabdominal cavity reaching to imaginary line joining anterior edges of coxae of chelipeds. Tubercle of pressbutton male abdominal locking mechanism rounded, on anterior edge of sternite 5.

Male abdomen distinctly T-shaped; telson triangular, slightly longer than broad, lateral margins gently concave, tip rounded; somite 6 rectangular, almost twice as long as broad, lateral margins gently 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; proximal three-quarters almost straight, distal quarter gently curving away from sternoabdominal cavity; outer margin with distinct indentation on proximal one-third; outer margin of subdistal margin with long setae; tip tapering to rounded 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, 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. Carapace usually with uniformly distributed rosette-like markings to different degrees; sometimes appearing almost uniformly olive green. Some specimens from the foothills of Gunong Serapi (ZRC 1989.2239–2246) were dark brown to brownish green in colour when live but the underlying pattern of rosette-like markings can still be discerned on the carapace, being distinct on the chelipeds and legs. The fingers of the chelipeds are usually pale brown. In some darker specimens, the dactylus is dark brown (never black), the distal part being beige.

Remarks. Lanchester (1900b: 255, pl. 12 fig. 2) described and figured a male specimen (37.5× 30.5 mm) from Kuching, Sarawak, of what he believed was Potamon (Parathelphusa) tridentatum var. incertum Lanchester, 1900a , noting that the structure of its external orbital angle was unusually sinuous. Nobili (1901: 10), however, on examining a specimen (36.0× 28.5 mm, sex not stated) from Sadong sent to him by Robert Shelford, argued that the Sarawak material differed from Lanchester’s taxon (which was described from Singapore) in several features: a sharper external orbital tooth with a longer and more sinuous margin, straighter postfrontal cristae, sharper and more prominently cut anterolateral teeth, and a carapace lacking spots. He also noted that his Sarawak taxon was closer to Parathelphusa maculata De Man, 1879 , than to P. tridentata H. Milne Edwards, 1853 , noting that the ambulatory merus of P. maculata had a strong subdistal spine that is absent in P. tridentata ( Nobili 1901: 9) . As such, Nobili (1901) referred the Sarawak specimens to a new subspecies, P. maculata oxygona . Nobili also referred western Borneo material identified by von Marten’s (1868) from Sinkawang as " Telphusa (Paratelphusa) tridentata " to this new subspecies.

As Nobili (1901) did not select a holotype, and he referred to the Borneo specimens examined by Lanchester (1900) and von Martens (1868) in his discussion, all this material as well as the one specimen he had from Sadong must be regarded as syntypes. Ng & Grinang (2004: 317) commented that there was no extant type material of the species and a neotype may need to be selected at a later date but this is not correct. Lanchester’s (1900) specimen from Kuching cannot be located. It is not in the Natural History Museum in London or the Zoology Museum at Cambridge University, and like the rest of Lanchester’s material from this collection, is probably no longer extant (see Ng 1989b: 70; 1990a: 54). There is, however, one Shelford specimen from Sadong in MUT (Cr 1211 Ex 1347) that is almost certainly the same one that was studied by Nobili (1901). Unfortunately, the specimen is in very bad condition, being crushed and in pieces. Although its size and sex cannot be ascertained, the pieces of the carapace remaining indicate it is identifiable with what is here defined as P. oxygona . Von Martens (1878) noted he had seven specimens from Sinkawang in western Borneo, some of which may have been sent to Wood-Mason (1876) (see discussion for next species). The only specimen Nobili (1901) himself had examined (MUT Cr 1211 Ex 1347) is here designated as the lectotype of P. oxygona . Although it is in very poor condition, it is clearly conspecific with what is here defined as P. oxygona . This is also in view of the present findings that von Martens’ (1868) Sinkawang material is not conspecific with P. oxygona but belongs to a new species, P. nobilii sp. nov.

Nobili’s (1901) taxon was accepted by Rathbun (1904) as a good species but dismissed by Colosi (1920) and Bott (1970) who included it under the synonymy of P. maculata and P. incerta , respectively. Bott (1970) regarded P. incerta as a distinct species, placing P. maculata under the synonymy of P. tridentata H. Milne Edwards, 1853 . Ng (1988, 1989a, 1990a), however, showed that P. maculata and P. incerta are actually subjective synonyms. Ng & Goh (1987), Ng (1988, 1990a, b, 2004), Chia & Ng (1998), Ng & Grinang (2004), Ng & Yeo (2007) and Ng et al. (2008) all treat P. oxygona as a valid taxon but no author has elaborated on its taxonomy; although Ng & Grinang (2004) did discuss the identity of the species but without a detailed redescription or figures. Ng (2004: 330, fig. 13C) provided a schematic figure of the G 1 in a key to Malaysian species but also did not elaborate on its taxonomy. The present paper addresses this shortcoming by providing a detailed redescription and figures of P. oxygona .

The structure of the external orbital tooth in P. oxygona is diagnostic, and the distinctly sinuous outer margin is a good character. It varies slightly in structure but not significantly, although in small specimens it is not reliable, being more evenly broadly triangular. Although the external orbital tooth of P. maculata somewhat approaches the condition in P. oxygona , the external margin is never as sinuous (see Ng 1990a: fig. 3A–K). In addition, the live coloration of these two taxa is very different. Although Nobili (1901: 10) commented that P. oxygona was not spotted while P. maculata was, this is not exactly correct. Ng (1988, 1989a, 1990a, b) has observed that large adults of P. maculata are a uniform greenish-brown to brown, while younger or smaller specimens may have their pereopods and part of their carapaces covered with small black spots. These spots never cluster together to form rosette-like patterns as frequently observed in live or freshly preserved P. oxygona ( Fig. 1 A). Some specimens, however, notably more darkly coloured individuals living on dark-coloured soils, do not show this pattern, and it can also be lost in long-preserved specimens; which may explain the condition of Nobili’s (1901: 10) specimen, which he noted was evenly brown. The more typical rosette-like pattern in P. oxygona has also been observed in P. reticulata Ng, 1990b , from Singapore and P. maindroni Rathbun, 1902 , from Sumatra and Peninsular Malaysia ( Ng 1990b, 1993), but these species differ markedly from P. oxygona in having a relatively more inflated carapace with the external orbital angle broadly triangular. The G1 structure of P. oxygona is also diagnostic, being one of the few species that possesses a distinct indentation or cleft on the proximal outer margin ( Fig. 4A, B ). This character is shared by P. maculata (see Ng 1990a: fig. 5A, B, E, F, H) and P. convexa De Man, 1879 (from Java) (unpublished data, see also Ng 1997: 120), but in P. oxygona , the G1 is proportionately more slender ( Figs. 4A–D , 5 ). The G1 of P. oxygona does vary slightly. Some specimens from the Sadong River in Sarawak have a slightly more sinuous G1, while others from the nearby localities have slightly straighter ones, although all are still gently curved ( Fig. 5 ). The indentation on the proximal outer margin is always present, although it can sometimes be relatively smaller (e.g., Fig. 5 F, J). The G1 structures of P. oxygona are never as stout as in P. maculata or as straight as P. nobilii sp. nov.

Specimens in the ZRC and MUT from the Sadong River identified as P. maculata by earlier workers are all clearly referable to P. oxygona . A pair of specimens from Sadong (MBA 981c) identified as Palawanthelphusa pulcherrima by Bott, but not listed in his 1970 study are actually P. oxygona . Colosi’s (1920) record of P. (P.) maculata is partly based on Nobili’s specimens and they are synonymised under P. oxygona accordingly. Nobili (1903) compared his new species, Parathelphusa modiglianii , from the Mentawei Islands off western Sumatra, with two specimens of " P. tridentata " from Borneo, and figured its cheliped carpus with a long sharp spine. As he had correctly separated P. tridentata from P. maculata by the absence of an ambulatory meral spine (present in P. maculata ) and P. modiglianii also lacks a spine, Nobili’s (1903) " P. tridentata " is more likely to be P. sarawakensis Ng, 1986 (from Sarawak), or P. nitida Ng, 1986 (from Kalimantan). Rathbun (1905) regarded specimens referred to P. oxygona by Nobili (1901) from Sarawak and a male from Sinkawang she examined in the Paris Museum as conspecific, which the present study has shown is not the case; the latter is now P. nobilii sp. nov. The collections on hand show that P. oxygona is confined to western Sarawak. Further west in Borneo (Indonesian Kalimantan), it appears to be replaced by P. nobilii sp. nov.

Specimens of P. oxygona were collected from muddy/sandy banks adjacent to relatively small and slow flowing lowland streams. The burrows can be several metres away from the edge of the water. The habitat and habits appear to be similar to species like P. maculata (see Ng 1989a, 1990a, c) and P. convexa (unpublished data). Ng & Yeo (2007) listed the species as vulnerable to extinction, noting that the primary threats are water pollution and habitat loss (see also Cumberlidge et al. 2009).

Figures

FIGURE 1. Overall dorsal views. A, Parathelphusa oxygona Nobili, 1901, male (36.6 × 28.0 mm) (ZRC 1992.10546), Serian, Sarawak; B, Parathelphusa nobilii sp. nov., holotype male (38.5 × 29.2 mm) (ZRC 1989.3751), Sinkawang, Kalimantan; C, Parathelphusa nobilii sp. nov., paratype female (40.5 × 30.3 mm) (ZRC 1989.3752), Sinkawang, Kalimantan.

FIGURE 2. A, C, E, Parathelphusa oxygona Nobili, 1901, male (36.6 × 28.0 mm) (ZRC 1992.10546), Serian, Sarawak; B, D, F, Parathelphusa nobilii sp. nov., holotype male (38.5 × 29.2 mm) (ZRC 1989.3751), Sinkawang, Kalimantan. A, B, lateral views of carapaces; C, D, frontal views of carapaces; E, F, right dorsal views of carapaces.

FIGURE 3. A, C, E, G, I, Parathelphusa oxygona Nobili, 1901, male (36.6 × 28.0 mm) (ZRC 1992.10546), Serian, Sarawak; B, D, F, H, J, Parathelphusa nobilii sp. nov., holotype male (38.5 × 29.2 mm) (ZRC 1989.3751), Sinkawang, Kalimantan. A, B, left third maxillipeds; C, D, left fourth ambulatory legs; E, right major chela; F, left major chela; G, H, anterior thoracic sternums and male abdominal somites 3 – 6 and telsons; I, J, posterior thoracic sternums and male abdominal somites 1 – 3.

FIGURE 4. A – E, Parathelphusa oxygona Nobili, 1901, male (36.6 × 28.0 mm) (ZRC 1992.10546), Serian, Sarawak; F – J, Parathelphusa nobilii sp. nov., holotype male (38.5 × 29.2 mm) (ZRC 1989.3751), Sinkawang, Kalimantan. A, F, ventral views of left G 1 s; B, G, dorsal views of left G 1 s; C, H, ventral views of distal parts of left G 1 s; D, I, dorsal views of distal parts of left G 1 s; E, J, left G 2 s. Scales: A, B, E, F, G, J = 1.0 mm; C, D, H, I = 0.5 mm.

FIGURE 5. G 1 s, Parathelphusa oxygona Nobili, 1901. A – D, male (31.4 × 24.8 mm) (ZRC 1989.2248), Gunung Serapi, Sarawak; E – H male (32.2 × 24.9 mm), Sadong, Sarawak; I, J, male (42.0 × 33.4 mm) (SM Cru 1986.6), Bidi, Sarawak; K, L, male (34.0 × 30.0 mm) (SM Cru 1986.115), Sarawak. A, ventral view of left G 1; B, dorsal view of left G 1; C, ventral view of distal part of left G 1; D, dorsal view of distal part of left G 1; E, I, K, dorsal views of right G 1 s; F, J, L, ventral views of right G 1 s; G, dorsal view of distal part of right G 1; H, ventral view of distal part of right G 1.