Johora tahanensis Bott, 1966

Ng, Peter K. L., 2020, Revision of the freshwater crabs of the Johora tahanensis (Bott, 1966) species group (Crustacea, Brachyura, Potamidae), with a key to the genus, ZooKeys 994, pp. 1-34 : 1

publication ID	https://dx.doi.org/10.3897/zookeys.994.56810
publication LSID	lsid:zoobank.org:pub:DB1879C9-1904-4320-BE67-4D9F863F6775
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scientific name	Johora tahanensis Bott, 1966
status

Treatment

Johora tahanensis Bott, 1966 Figures 1B View Figure 1 , 2B View Figure 2 , 3B View Figure 3 , 4B View Figure 4 , 5B View Figure 5 , 8A-D View Figure 8 , 12B View Figure 12 , 13B View Figure 13 , 14B View Figure 14

Potamiscus (Johora) johorensis tahanensis Bott, 1966: 495 (part), pl. 21 fig. 15.

Stoliczia (Johora) johorensis tahanensis - Bott 1970: 181 (part), pl. 50 fig. 50.

Johora tahanensis - Ng 1987: 33 (part), fig. 9A; Ng 1988: 42 (part), fig. C, F; Ng and Takeda 1992: 107 (part); Ng 2004: 321; Ng and Yeo 2007: 102; Ng et al. 2008: 163; Cumberlidge et al. 2009: table.

Stoliczia johorensis tahanensis - Takeda 1987: 92, pl. X (center).

Material examined.

13 males (largest 27.2 × 22.9 mm), 13 females (largest 24.4 × 21.0 mm), 4 juveniles (ZRC 1984.6764-6793), Kuala Tahan, Taman Negara National Park, Pahang, coll. Tweedie MWF, April 1940; 1 male (30.7 × 25.5 mm), 2 females (ZRC 1984.6795-6797), rivulet of Sungei Tahan, Kuala Tahan, Taman Negara National Park, Pahang, coll. Alfred ER, 23 March 1956; 1 male (ZRC 1989.2086), Changah Siveh, Sungei Tahan, Taman Negara National Park, Pahang, coll. Alfred ER, 3 March 1948; 1 female (ZRC 1989.3749), Jenka, Sungei Tekam, Pahang, 4°13'N, 102°39'E, coll. Lim RP, 19 March 1981; 1 young male, 1 female (ZRC 1989.2144-2145), from University of Malaya collections, 1960s; 2 juveniles (ZRC 1989.3358-3359), station F63/20, tributary of Sungei Telom (= Sungei Telum), Pahang, coll. University of Malaya, 9 March 1963; 1 female (ZRC 1989.3686), coll. University of Malaya, no date. All locations in Peninsular Malaysia.

Diagnosis.

Adult carapace width to length ratio 1.16-1.19 (Figs 1B View Figure 1 , 2B View Figure 2 , 12B View Figure 12 ); dorsal surface gently convex in frontal view, not inflated (Fig. 3B View Figure 3 ); frontal margin almost straight (Fig. 2B View Figure 2 ); suborbital, pterygostomial and sub-branchial regions rugose, pterygostomial region covered with dense setae (Fig. 3B View Figure 3 ); epigastric cristae distinct, distinctly anterior to sharp postorbital cristae, postorbital cristae with lateral edges low, joining lateral margin through oblique striae (Fig. 2B View Figure 2 ); external orbital tooth separated from epibranchial tooth by distinct cleft, epibranchial tooth sharp, distinct (Fig. 2B View Figure 2 ); anterolateral margin distinctly convex (Fig. 2B View Figure 2 ); posterolateral margin gently sinuous to almost straight, distinctly converging towards gently convex, entire posterior carapace margin (Fig. 2B View Figure 2 ); posterior margin of epistome with triangular median triangle, lateral margin obliquely sloping (Fig. 3B View Figure 3 ); outer surfaces of third maxillipeds with dense, long stiff setae; ischium subrectangular, with shallow median oblique groove (Figs 3B View Figure 3 , 4B View Figure 4 ); ambulatory legs not elongate, length to width ratio of merus of fourth ambulatory leg 2.7-2.8 (Figs 1B View Figure 1 , 12B View Figure 12 ); G1 subterminal segment gradually tapering from broad proximal part to slender distal part, without distinct shelf-like structure along gently concave outer margin; terminal segment gently curved outwards (from median part of sternum), ca. half length of subterminal segment, surface with numerous short setae (Fig. 8A-C View Figure 8 ); G2 slightly longer than G1, distal segment long, about half length of basal segment (Fig. 8D View Figure 8 ). Female pleon longitudinally ovate; somites 3-6 progressively narrower; telson subtriangular (Fig. 13B View Figure 13 ). Vulvae large, on anterior half of sternite 6, slightly pushing into suture with sternite 5, lateral sternal vulvar cover semicircular (Fig. 14B View Figure 14 ).

Description of male.

Carapace subrectangular broader than long, width to length ratio 1.16-1.19; dorsal surface gently convex in frontal view (Figs 1B View Figure 1 , 2B View Figure 2 , 3B View Figure 3 ). Frontal margin almost straight; frontal region, dorsal surface, lateral parts of anterolateral and branchial regions rugose, covered with small granules and striae; regions clearly indicated, median H-shaped gastro-cardiac groove deep; cervical grooves broad, shallow; suborbital, pterygostomial and sub-branchial regions rugose, covered with dense setae (Figs 2B View Figure 2 , 3B View Figure 3 ). Epigastric cristae distinct, marked by transverse striae, not cristate, separated by median groove; postorbital cristae sharp, prominent, positioned distinctly posterior to and separated from epigastric cristae, lateral edges reaching beginning of cervical groove, reaching lateral margin through series of short, oblique striae (Figs 1B View Figure 1 , 2B View Figure 2 ). Frontal margin entire; separated from supraorbital margin by rounded angle (Fig. 2B View Figure 2 ). External orbital tooth triangular, outer margin twice length of inner margin; epibranchial tooth sharp, distinct, separated from anterolateral margin by distinct cleft (Figs 1B View Figure 1 , 2B View Figure 2 ). Anterolateral margins convex, cristate, granulated (Fig. 2B View Figure 2 ). Posterolateral margin gently sinuous to almost straight, distinctly converging towards gently convex, entire posterior carapace margin (Figs 1B View Figure 1 , 2B View Figure 2 ). Orbits subovate; eye filling up most of orbital space; ocular peduncle relatively short, stout; cornea large, pigmented (Fig. 3B View Figure 3 ). Supraorbital margin concave, entire (Fig. 2B View Figure 2 ). Suborbital margin concave, complete, cristate (Fig. 3B View Figure 3 ). Antennules short, folding transversely in narrow fossa; antennae very short, not reaching cornea of eyes (Fig. 3B View Figure 3 ). Posterior margin of epistome with triangular median lobe; lateral part obliquely sloping, with 2 distinct concave margins (Fig. 3B View Figure 3 ). Mandibular palp with 3 distinct articles, terminal article single lobed.

Third maxillipeds covering most of buccal cavity when closed; surfaces of merus, ischium and exopod with numerous long stiff setae; ischium subrectangular, with shallow median oblique groove; merus subquadrate, slightly wider than long, anteroexternal angle not expanded; exopod slender, reaching half length of merus, with long flagellum (Figs 3B View Figure 3 , 4B View Figure 4 ).

Chelipeds asymmetrical (Fig. 1B View Figure 1 ). Anterior margin of basis-ischium smooth; margins of merus rugose, uneven; inner margin lined with dense setae. Outer surface of carpus rugose, inner distal angle with sharp tooth (Fig. 1B View Figure 1 ). Outer surfaces of chelae rugose; chela stout (Fig. 1B View Figure 1 ). Fingers of chela almost straight, longer than palm; cutting edges of both fingers with variously sized teeth and denticles; fingers of slightly smaller chela similar (Fig. 1B View Figure 1 ).

Ambulatory legs not elongate, length to width ratio of merus of fourth ambulatory leg 2.7-2.8; second pair longest, fourth pair shortest (Fig. 1B View Figure 1 ). Surface of merus gently rugose, dorsal margin weakly cristate, slightly uneven, appears serrated, without subdistal spine or tooth; carpus rugose with short setae; propodus laterally flattened, margins with short setae; dactylus gently curved, setose, margins with short spines (Fig. 1B View Figure 1 ).

Thoracic sternum (notably sternites 3, 4) with shallow pits to smooth (Fig. 5B View Figure 5 ). Sternites 1, 2 completely fused to form triangular plate with convex margins; separated from sternite 3 by distinct, gently concave suture lined with short setae; sternites 3, 4 completely fused except for shallow oblique depression between sternites, lined with short stiff setae (Fig. 5B View Figure 5 ); sutures between sternites 4/5, 5/6, 6/7 medially interrupted; suture between sternites 7, 8 complete; deep longitudinal groove on sternite 8 extending to most of sternite 7. Penis on condyle of coxa of fourth ambulatory leg. Sternopleonal cavity deep, reaching to imaginary line connecting submedian parts of cheliped coxae (Fig. 5B View Figure 5 ). Male pleonal locking tubercle relatively large, low, round, positioned on posterior edge of sternite 5, just adjacent to sternite 6.

Pleon triangular, all somites, telson free; telson triangular, lateral margins almost straight to gently sinuous; somite 6 subtrapezoidal, distinctly wider than long, lateral margins gently sinuous; somites 3-5 trapezoidal, gradually decreasing in width; somites 1, 2 subrectangular, narrow, very wide, reaching to bases of coxae of fourth ambulatory legs, thoracic sternite 8 not visible when pleon closed (Fig. 5B View Figure 5 ).

G1 subterminal segment gradually tapering from broad proximal part to slender distal part, without distinct shelf-like structure along gently concave outer margin; terminal segment gently curved outwards (from median part of sternum), ca. half length of subterminal segment, surfaces with numerous short setae (Fig. 8A-C View Figure 8 ); G2 slightly longer than G1, distal segment long, about half length of basal segment (Fig. 8D View Figure 8 ).

Female. Similar to male in most non-sexual features; chelipeds symmetrical or only slightly asymmetrical (Fig. 12B View Figure 12 ). Pleon longitudinally ovate, covering most of thoracic sternal surface, all somites and telson free; somites 3-6 progressively narrower; telson subtriangular (Fig. 13B View Figure 13 ). Vulvae large, covering anterior half of sternite 6, slightly pushing into suture with sternite 5, lateral sternal vulvar cover semicircular (Fig. 14B View Figure 14 ).

Remarks.

Ng and Takeda (1992: 108) discussed the taxonomy of J. tahanensis at length, showing that the material from two parts of Taman Negara National Park in Malaysia belonged to two species and that the type series is mixed. Bott (1966, 1970) and Ng (1987, 1988) had regarded them as one taxon, incorrectly noting that the G1 structure was variable. The holotype of J. tahanensis was from Kuala Tahan in the state of Pahang, in the southern part of the national park, and the G1 of this specimen (in the Senckenberg Museum, Frankfurt) as well as the topotypic material we have from that location has a terminal segment which is gently curved (Fig. 8A View Figure 8 ). Material from the northern part of the park from the adjacent state of Kelantan had a G1 terminal segment that is straight (Fig. 8E View Figure 8 ). Ng and Takeda (1992) showed that the G1 differences of the Pahang and Kelantan specimens are consistent and the Kelantan material was referred to a separate species, J. hoiseni .

The material reported as " J. tahanensis " by Ng and Takeda (1992: 108) from and around Fraser’s Hill in Selangor and Pahang should be now referred to J. booliati sp. nov. (see remarks for this species).

Distribution.

Johora tahanensis is known from the tributaries around Sungei Tahan in southern Pahang, at the southern part of Taman Negara National Park (Fig. 15 View Figure 15 ). It lives among rocks and submerged vegetation in the relatively fast flowing streams in the forest.

Conservation.

The species is not under any immediate threat as it is found in Malaysia’s oldest and largest national park. Ng and Yeo (2007) treated J. tahanensis s. str. as vulnerable as it is not known from a relatively wide geographic area but it was reappraised and regarded as of least concern in Cumberlidge et al. (2009).