Cantopotamon yangxiense, 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 : 12-16

publication ID	https://doi.org/ 10.6620/ZS.2017.56-41
persistent identifier	https://treatment.plazi.org/id/9B11878D-FFC1-FFF2-44CD-B288FEF6FD21
treatment provided by	Felipe
scientific name	Cantopotamon yangxiense
status	sp. nov.

Treatment

Cantopotamon yangxiense View in CoL n. sp.

( Figs. 7-8 View Fig View Fig , 9D View Fig , 10D View Fig , 11D View Fig , 12D View Fig )

urn:lsid:zoobank.org:act:FD44220C-7E73-49A2-9E89-2874964EA328

Type material: Holotype: SYSBM 001562 , male (19.3 × 16.0 mm), E’huang Ridge (21.82°N, 111.44°E), Yangxi, Yangjiang City, Guangdong, small hillstreams, under rocks, coll. C. Huang, May, 2015 GoogleMaps . Paratypes: SYSBM 001563, 1 female (18.5 × 14.9 mm), same data as holotype. ZRC, 1 male (17.0 × 14.1 mm), same data as holotype. ZRC, 1 female (19.8 × 16.0 mm), same data as holotype.

Other material examined: 1 male (20.5 × 17.0 mm) ( SYSBM 001564), same data as holotype. 2 females (18.3 × 15.1 mm, 16.9 × 13.8 mm) ( SYSBM 001565-001566), same data as holotype. 2 males (16.7 × 13.9 mm, 16.4 × 13.4 mm) ( SYSBM 001567-001568), Longgao Mountain (21.67°N, 111.67°E), Yangxi, Yangjiang City, Guangdong, small hillstreams, under rocks, coll. C. Huang, May, 2015. 2 females (15.4 × 12.4 mm, 13.6 × 11.4 mm) ( SYSBM 001569- 001570), same data as above.

Etymology: This species is named after the type locality Yangxi, Yangjiang, Guangdong Province.

Diagnosis: Third maxilliped merus width about 1.1 × length; ischium width about 0.7 × length ( Figs. 7B View Fig , 8D View Fig ). Major cheliped palm length about 1.3 × height ( Fig. 7A View Fig ). Male pleonite 6 width about 2 × length; telson width about 1.4 × length, apex rounded ( Fig. 7C View Fig ). Tip of G1 terminal segment reaching well beyond tubercle forming pleonal locking structure in situ, exceeding sternal suture 4/5 ( Fig. 7D View Fig ); subterminal segment about 2.3 times as long as terminal segment, inner proximal section curved dorsally; terminal segment inner margin with sub-distal blunt projection, tip blunt ( Figs. 7D View Fig , 8B, C View Fig , 9G, H View Fig ). G2 basal segment subovate, about 2.6 times length of flagelliform distal segment ( Fig. 8A 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. 7A View Fig ). Front slightly deflexed, margin slightly ridged on dorsal view ( Fig. 7A View Fig ). Epigastric cristae distinct, separated by narrow gap ( Figs. 7A, B View Fig ). Postorbital cristae sharp, laterally expanded, fused with epigastric cristae and epibranchial teeth ( Figs. 7A, B View Fig ). Branchial regions relatively flat ( Fig. 7A View Fig ). Cervical groove shallow, inconspicuous ( Fig. 7A View Fig ). Mesogastric region slightly convex ( Fig. 7A View Fig ). External orbital angle triangular ( Fig. 7A View Fig ). Epibranchial tooth small, granular, but distinct ( Figs. 7A, B View Fig ). Anterolateral margin distinctly cristate, lined with approximately 20-24 granules; lateral part bent inward ( Fig. 7A View Fig ). Posterolateral margin comparatively smooth, lined with oblique striae, converging towards posterior carapace margin ( Fig. 7A View Fig ). Orbits small; supraorbital and infraorbital margins cristate, lined with numerous inconspicuous granules ( Fig. 7B View Fig ). Sub-orbital and upper parts of pterygostomial regions covered with large rounded granules, sub-hepatic region lined with oblique striae ( Fig. 7B View Fig ).

Third maxilliped merus width about 1.1 × length; ischium width about 0.67 × 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. 7B View Fig , 8D View Fig ). Posterior margin of epistome narrow; median lobe sharply triangular, lateral margins almost straight ( Fig. 7B View Fig ).

Chelipeds (pereopod 1) unequal ( Fig. 7A View Fig ). Merus cross-section trigonal; margins crenulated ( Fig. 7B View Fig ). Carpus with sharp distomesial spine and spinule at base, dorsal surface with curved striae ( Fig. 7A View Fig ). Major cheliped palm length about 1.3 × height ( Fig. 7A View Fig ). Movable finger as long as fixed finger ( Fig. 7A View Fig ). Occlusal margin of fingers with rounded, blunt teeth; with small gape when closed ( Fig. 7A View Fig ).

Ambulatory legs (pereopods 2-5) slender; dactylus with dense short setae; propodus, carpus and merus with relatively sparse, short setae ( Fig. 7A View Fig ). Pereopod 5 propodus length about 1.9 × width, subequal to dactylus ( Fig. 7A View Fig ).

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

Male pleon triangular, almost reaching anteriorly to level of posterior margins of cheliped coxae; pleonites 3-6 progressively broader longitudinally, lateral margins straight; somite 6 width about 2 × length; telson width about 1.4 × length, apex rounded ( Fig. 7C View Fig ).

G1 straight, tip of terminal segment reaching well beyond tubercle forming pleonal locking structure in situ, exceeding sternal suture 4/5 ( Fig. 7D 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, pointing anteriorly, inner margin with sub-distal blunt projection, tip blunt ( Figs. 7D View Fig , 8B, C View Fig , 9G, H View Fig ). G2 basal segment subovate, about 2.6 times length of flagelliform distal segment ( Fig. 8A View Fig ).

Size range: Male (n = 5) 16.4 × 13.4 to 20.5 × 17.0 mm; female (n = 6) 13.6 × 11.4 to 19.8 × 16.0 mm.

Remarks: Cantopotamon yangxiense n. sp. is closest to C. zhuhaiense n. sp. in overall external morphology, but can be separated by its longer G1, which reaches in situ well beyond the tubercle forming the pleonal locking structure ( Fig. 7D View Fig ) [versus not reaching in C. zhuhaiense n. sp. ( Fig. 1D View Fig )]; the blunt projection on the inner margin of the G1 terminal segment ( Fig. 8C View Fig ) [versus broadly triangular margin in C. zhuhaiense n. sp. ( Fig. 2C View Fig )]; and other characters as shown in table 2.

Colour in life: Generally mottled brown ( Fig. 12D View Fig ).

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

Distribution: Yangxi, Yangjiang, Guangdong.

Phylogenetic relationships

In the present phylogenetic analyses, 65 species from 49 potamid genera were included. A 502 bp segment, excluding the variable regions, of the 16S rDNA was amplified and aligned. The BI and ML analyses based on 16S sequences resulted in similar topologies ( Fig. 13 View Fig ). Monophyly of Cantopotamon is well supported as part of the “China-East Asia Islands” clade ( Shih et al. 2009), although its position among these genera is ambiguous based on present data. Combined analysis of the 16S and COI data also supports the validity of the four new species ( Fig. 14 View Fig ), with two pairs of sister species, C. zhuhaiense + C. hengqinense , and C. shangchuanense + C. yangxiense . Minimum interspecific K2P and p-distance divergences in COI between the four new species is 7.73% and 7.29%, respectively, with bp difference of 48 bp between C. zhuhaiense and C. hengqinense .