Cantopotamon hengqinense, Huang & Ahyong & Shih, 2017

Huang, Chao, Ahyong, Shane T. & Shih, Hsi-Te, 2017, , A New Genus of Freshwater Crabs from Guangdong, China, with Descriptions of Four New Species (Crustacea: Decapoda: Brachyura: Potamidae)., Zoological Studies 56 (41), pp. 1-20 : 9-12

publication ID	https://doi.org/ 10.6620/ZS.2017.56-41
persistent identifier	https://treatment.plazi.org/id/9B11878D-FFC2-FFE8-44E1-B148FCF8FE61
treatment provided by	Felipe
scientific name	Cantopotamon hengqinense
status	sp. nov.

Treatment

Cantopotamon hengqinense View in CoL n. sp.

( Figs. 5-6 View Fig View Fig , 9C View Fig , 10C View Fig , 11C View Fig , 12C View Fig )

urn:lsid:zoobank.org:act:9520E984-450A-4058-B298-6B1C86FA0B85

Type material: Holotype: SYSBM 001558 , male (19.9 × 16.0 mm), Dahengqin Mountain (22.11°N, 113.50°E), Hengqin Island , Zhuhai City, Guangdong, small hillstream, under rocks, coll. C. Huang, Feb, 2016 GoogleMaps . Paratypes: SYSBM 001559, 1 female (13.0 × 10.6 mm), same data as holotype. SYSBM 001560-001561, 2 males (15.5 × 12.4 mm, 13.2 × 10.7 mm), same data as holotype.

Other material examined: SYSBM 001640, 1 male (17.5 × 13.6 mm), Hengqin Island, Zhuhai City, Guangdong, small hillstream, under rocks, coll. C. Huang, Aug, 2017. SYSBM 001641-1644, 4 females (20.5 × 16.0 mm, 15.1 × 11.8 mm, 14.1 × 10.8 mm, 12.3 × 10.0 mm), same as above male.

Etymology: This species is named after the type locality, Hengqin Island (also known as Ilha de Montanha in Portuguese), Zhuhai City, Guangdong Province, China.

Diagnosis: Third maxilliped merus width about 1.1 × length; ischium width about 0.71 × length ( Figs. 5B View Fig , 6D View Fig ). Major cheliped palm length about 1.3 × height ( Fig. 5A View Fig ). Male pleonite 6 width about 2.5 × length; telson width about 1.6 × length ( Fig. 5C View Fig ). Tip of G1 terminal segment (in situ) reaching well beyond tubercle forming pleonal locking structure, exceeding sternal suture 4/5 ( Fig. 5D View Fig ); subterminal segment about 2.3 times as long as terminal segment, inner proximal section curved dorsally; terminal segment curved inwards and pointing anteriorly, outer proximal region swollen, with strongly convex margins, tip horn-shaped ( Figs. 5D View Fig , 6B, C View Fig , 9E, F View Fig ). G2 basal segment subovate, about 2.6 times length of flagelliform distal segment ( Fig. 6A View Fig ).

Description of male: Carapace broader than long, regions indistinct; dorsal surface slightly convex transversely and longitudinally; surface generally smooth with fused rugae on anterolateral region ( Fig. 5A View Fig ). Front slightly deflexed, margin slightly ridged on dorsal view ( Fig. 5A View Fig ). Epigastric cristae distinct, separated by narrow gap ( Figs. 5A, B View Fig ). Postorbital cristae sharp, laterally expanded, fused with epigastric cristae and epibranchial teeth ( Figs. 5A, B View Fig ). Branchial regions relatively flat ( Fig. 5A View Fig ). Cervical groove shallow, inconspicuous ( Fig. 5A View Fig ). Mesogastric region slightly convex ( Fig. 5A View Fig ). External orbital angle triangular ( Fig. 5A View Fig ). Epibranchial tooth small, granular, but distinct ( Figs. 5A. B View Fig ). Anterolateral margin distinctly cristate, lined with approximately 19-21 granules; lateral part bent inward ( Fig. 5A View Fig ). Posterolateral margin comparatively smooth, lined with oblique striae, converging towards posterior carapace margin ( Fig. 5A View Fig ). Orbits small; supraorbital and infraorbital margins cristate, lined with numerous inconspicuous ( Fig. 5B View Fig ). Sub-orbital and upper parts of pterygostomial regions covered with large rounded granules, sub-hepatic region lined with oblique striae ( Fig. 5B View Fig ).

Epistome posterior margin narrow; median lobe sharply triangular, lateral margins almost straight ( Fig. 5B View Fig ).

Third maxilliped merus width about 1.1 × length; ischium width about 0.7 × length; merus trapezoidal, with median depression; ischium trapezoidal, with distinct median sulcus; exopod reaching to proximal third of merus, flagellum long; dorsomesial margin of ischium subauriculiform ( Figs. 5B View Fig , 6D View Fig ).

Chelipeds (pereopod 1) unequal ( Fig. 5A View Fig ). Merus cross-section trigonal; margins crenulated ( Fig. 5B View Fig ). Carpus with sharp distomesial spine and spinule at base, dorsal surface with curved striae ( Fig. 5A View Fig ). Major cheliped palm length about 1.3 × height ( Fig. 5A View Fig ). Movable finger as long as fixed finger ( Fig. 5A View Fig ). Occlusal margin of fingers with rounded, blunt teeth; with very slight gape when closed ( Fig. 5A View Fig ).

Ambulatory legs (pereopods 2-5) slender; dactylus with dense short setae; propodus, carpus and merus with relatively sparse short setae ( Fig. 5A View Fig ). Pereopod 5 with propodus length about 2 × width, subequal to dactylus ( Fig. 5A View Fig ).

Thoracic sternum generally smooth, weakly pitted; sternites 1, 2 completely fused, triangular; sternites 3, 4 fused without obvious median suture ( Figs. 5C View Fig , 10C View Fig ). Male sterno-pleonal cavity reaching anteriorly to midlength of chelipeds coxae; median longitudinal groove between sternites 7, 8 deep ( Fig. 5D View Fig ). Pleonal locking tubercle slightly posterior to mid-length of sternite 5 ( Fig. 5D View Fig ).

Male pleon triangular, almost reaching anteriorly to level of posterior margin of cheliped coxae; pleonites 3-6 progressively broader longitudinally, lateral margins straight; somite 6 width about 2.5 × length; telson width about 1.6 × length, apex rounded ( Fig. 5C View Fig ).

G1 tip of terminal segment reaching well beyond tubercle forming pleonal locking structure in situ, exceeding sternal suture 4/5 ( Fig. 5D View Fig ); subterminal segment about 2.3 times as long as terminal segment, inner proximal section curved dorsally; terminal segment relatively short, sinistrally twisted on the left G1, curved inwards and pointing anteriorly, outer proximal region swollen, with strongly convex margins, tip horn-shaped ( Figs. 5D View Fig , 6B, C View Fig , 9E, F View Fig ). G2 basal segment subovate, about 2.6 times length of flagelliform distal segment ( Fig. 6A View Fig ).

Size range: Male (n = 4) 13.2 × 10.7 to 19.9 × 16.0 mm; female (n = 5) 12.3 × 10.0 to 20.5 × 16.0 mm.

Remarks: Cantopotamon hengqinense n. sp. is closest to C. zhuhaiense n. sp., in overall external morphology, but can be separated by a unique combination of characters as outlined under the Remarks section of C. zhuhaiense n. sp. and table 2.

Colour in life: Mottled brown overall ( Fig. 12C View Fig ).

Ecology: This species is mainly aquatic, living under rocks in small hillstreams.

Conservation status: Currently, only 8% of Chinese freshwater crabs are assessed as threatened according to IUCN criteria, though the true percentage is likely much higher due to the high proportion of data deficient species ( Cumberlidge 2016). Situated south of Zhuhai City and adjacent to Macau, Hengqin Island is the largest of the 146 islands in Zhuhai. It was formerly composed of two islands: Xiaohengqin and Dahengqin, but was joined as one through land reclamation. It has seen rapid economic development in recent years with a significant degree of urbanization. The human population of the island was less than 8,000 in 2008, but this number is expected to rise to 280,000 by 2020. Dahengqin Mountain is situated at the far south of Hengqin Island and covers an area of around 25 km 2. The mountain is isolated, surrounded by sea to the east, west and south, and by residential areas to the north. Surveys conducted around the region indicate that C. hengqinense likely has an area of occupancy of only around 15 km 2, being only known from three hillstreams in close proximity on Dahengqin Mountain. This extremely restricted distribution makes this species highly vulnerable to habitat degradation and destruction. According to the official development plans for Hengqin Island, an ecological park is to be built for tourism on Dahengqin Mountain. Although the plan does state conservation as a priority, the alteration of the original habitat coupled by the significant increase in human activity in the area will no doubt impact the habitat. Given the limited area of occurrence and expected rise in the island’s human population, the area of occupancy and quality of the habitat of C. hengqinense can be reasonably projected to decline. Therefore, the conservation status of C. hengqinense under IUCN Red List criteria corresponds to Endangered B2(a) (b).

Distribution: Hengqin Island, Zhuhai, Guangdong.