Johora thoi Ng, 1990

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
persistent identifier	https://treatment.plazi.org/id/EF6BEDB2-6B88-5D0D-9F4C-B693F42CC32C
treatment provided by	ZooKeys by Pensoft
scientific name	Johora thoi Ng, 1990
status

Treatment

Johora thoi Ng, 1990 Figures 1C View Figure 1 , 2C View Figure 2 , 3C View Figure 3 , 4C View Figure 4 , 5C View Figure 5 , 6 View Figure 6 , 9A-H View Figure 9 , 12C View Figure 12 , 13C View Figure 13 , 14C View Figure 14

Johora thoi Ng, 1990: 305, figs 1, 2; Ng 2004: 321; Ng and Yeo 2007: 102; Ng et al. 2008: 163; Cumberlidge et al. 2009: table.

Material examined.

Holotype: male (41.2 × 33.3 mm) (ZRC 1989.2249), Telok Kalong Besar, Pulau Redang, Terengganu, ca. 5°46'7"N, 103°01'38"E, coll. Tho YP, 8 March 1989. Others: 1 male (ZRC 1989.3758), in freshwater stream, Telok Kalong Besar, Pulau Redang, Terengganu, coll. Saw LG, 1 August 1989; 1 male (ZRC 1989.3740), Telok Kalong Besar, Pulau Redang, Terengganu, coll. Saw LG, 1 August 1989; 1 male, 1 female (ZRC 1996.2085), site 5, stream behind Pasir Panjang, Pulau Redang, Terengganu, Lim KKP et al., 25 June 1992; 1 male (ZRC 1996.2087), Pulau Redang, Terengganu, Lim KKP et al., 23 June 1992; 3 males (ZRC 1996.2086), site 7, stream behind Telok Kalong Besar, Pulau Redang, Terengganu, coll. Lim KKP et al., 25 June 1992; 6 males, 2 females, 1 juvenile (ZRC 2001.1167), from freshwater rocky stream, East Coast forest trail, ca. 1.2-1.6 km from Pasir Panjang to Telok Dalam, Pulau Redang, Terengganu, coll. Tan HH and Koh LL, 20 June 2001. All locations in Peninsular Malaysia.

Diagnosis.

Adult carapace width to length ratio 1.19-1.24 (Figs 1C View Figure 1 , 2C View Figure 2 , 6A, B View Figure 6 , 12C View Figure 12 ); dorsal surface gently convex in frontal view, not inflated (Figs 3C View Figure 3 , 6C View Figure 6 ); frontal margin almost straight or slightly sinuous (Figs 2C View Figure 2 , 6B View Figure 6 ); suborbital, pterygostomial and sub-branchial regions rugose, pterygostomial region covered with dense setae (Figs 3C View Figure 3 , 6C View Figure 6 ); epigastric cristae distinct, distinctly anterior to sharp postorbital cristae, postorbital cristae with lateral edges low, not joining lateral margin (Figs 2C View Figure 2 , 6B View Figure 6 ); external orbital tooth separated from epibranchial tooth by prominent cleft, epibranchial tooth sharp, distinct (Figs 2C View Figure 2 , 6B View Figure 6 ); anterolateral margin distinctly convex (Figs 2C View Figure 2 , 6B View Figure 6 ); posterolateral margin gently sinuous to almost straight, distinctly converging towards gently convex, entire posterior carapace margin (Figs 2C View Figure 2 , 6B View Figure 6 ); posterior margin of epistome with triangular median triangle, lateral margin obliquely sloping (Figs 3C View Figure 3 , 6C View Figure 6 ); outer surfaces of third maxillipeds with dense, long stiff setae; ischium subrectangular, with shallow median oblique groove (Figs 3C View Figure 3 , 4C View Figure 4 ); ambulatory legs relatively longer, length to width ratio of merus of fourth ambulatory leg 3.0-3.2 (Figs 1C View Figure 1 , 6A View Figure 6 , 12C View Figure 12 ); G1 subterminal segment with broad proximal part, tapering suddenly to slender distal part, with distinct shelf-like structure along outer margin; terminal segment straight, long, slender, subequal in length to subterminal segment, surfaces with scattered short setae (Fig. 9A-C, E-G View Figure 9 ); G2 shorter than G1, distal segment long, about two-thirds length of basal segment (Fig. 9D, H View Figure 9 ). Female pleon ovate; somites 3-6 progressively narrower; telson semi-circular (Fig. 13C View Figure 13 ). Vulvae large, on anterior half of sternite 6, adjacent to suture with sternite 5, lateral sternal vulvar cover triangular, partially overlapping sternite 5 (Fig. 14C View Figure 14 ).

Remarks.

This is one of the largest species of Johora and is rivalled in size only by J. tiomanensis and J. counsilmani from Pulau Tioman. The G1 structure of J. thoi is distinctive and consistent, the long and straight terminal segment being evident even in small subadult specimens (Fig. 9E-G View Figure 9 ). The only other species with superficially similar G1s are J. singaporensis and J. michaeli sp. nov. from Singapore and mainland Terengganu, respectively. In these species, however, the G1 terminal segment is prominently shorter, being only two-thirds or less the length of the subterminal segment (Fig. 9I-K View Figure 9 ; Ng 1987: fig. 8A, B).

Distribution.

Johora thoi is endemic to Pulau Redang, the largest island in the Redang Archipelago, a group of nine islands about 25 km off the northeastern coast of Peninsular Malaysia. The species has been recorded from most parts of the island, including its highest point (359 m), occurring in all clean waters there (Fig. 15 View Figure 15 ). It lives under rocks and can be found along the stream banks at night.

Conservation.

Although the entire Redang Archipelago is a marine park, the forests are not fully protected, and development of the land for tourism and excessive freshwater use are concerns. As the species is only known from one island only 7 km long and 6 km wide, it is treated as endangered by Ng and Yeo (2007), but Cumberlidge et al. (2009) noted it was vulnerable at best as the area is technically protected.