Parvuspotamon yuxiense Dai & Bo, 1994

Figs 2, 3, 4

Type material.

Holotype. China • ♂, 15.7 × 12.9 mm; Yunnan Province, Yuxi City, Xinping County, Gasa Township; Aug. 1990; CB05138 YN 9091116A.

Additional material.

China • 4 ♂, 26.18 × 19.73 mm (NNU-3151-01), 23.26 × 17.19 mm (NNU-3151-02), 22.68 × 17.02 mm (NNU-3151-03), 20.79 × 15.52 mm (NNU-3151-04) , 3 ♀, 22.82 × 16.98 (NNU-3151-05), 21.13 × 16.47 (NNU-3151-06), 22.59 × 17.35 (NNU-3151-07); Yunnan Province, Yuxi City, Xinping County, Heshalak Village; 23.96°N, 101.45°E; altitude 955 m asl; 11 Apr. 2019; Boyang Shi, Xiyang Hao, Zewei Zhang, and Hongying Sun, leg. • 5 ♂, 24.94 × 18.94 mm (NNU-1513-01), 21.16 × 16.86 mm (NNU-1513-02), 22.02 × 16.06 mm (NNU-1513-03), 18.72 × 13.42 mm (NNU-1513-04), 16.58 × 11.98 mm (NNU-1513-05), 2 ♀, 22.54 × 16.63 mm (NNU-1513-06), 17.12 × 12.77 mm (NNU-1513-07); Yunnan Province, Yuxi City, Gasha Town; 24.02°N, 101.58°E; altitude 795 m asl; 15 Oct. 2015; Kelin Chu, Qiang Zhao, Pengfei Wang, and Hongying Sun leg.

Description.

Medium sized (adult carapace width 16-26 mm, n = 15). Carapace broader than long, ovate; dorsal surface convex both transversely and longitudinally, smooth, regions not clear; branchial regions swollen, smooth (Figs 2A, 4A). Postorbital and epigastric cristae confluent (Figs 2A, 4A); epigastric cristae weakly developed, oblique, separated by deep inverted Y-shaped groove (Figs 2A, 4A); postorbital cristae low, indistinct (Figs 2A, 4A). External orbital angle bluntly triangular, outer margin and anterolateral margin of carapace confluent (Figs 2A, 4A). Anterolateral margin of carapace entire convex, smooth; posterolateral margin gently concave, smooth, converging towards posterior carapace margin (Figs 2A, 4A). Epibranchial tooth indistinct (Figs 2A, 4A). Orbits large; supraorbital and infraorbital margins smooth; sub-orbital, sub-hepatic, and pterygostomial regions smooth (Figs 2B, C, 4B, C). Antennular fossae slit-like in anterior view; median lobe of epistome posterior margin narrowly triangular (Figs 2B, 4B). Third maxilliped with rhombus ischium; exopod reaching beyond anterolateral corner of ischium, without flagellum (Fig. 3G).

Chelipeds unequal (Figs 2A-C, 3A, B, 4A-C). Merus trigonal in cross section; margins weakly crenulated (Figs 2A, 4A). Carpus with sharp spine at inner-distal angle (Figs 2A, 4A). Major cheliped palm length ~ 1.3 × height (Fig. 3B). Occlusal margin of fingers with several small teeth; distinct gape when closed (Fig. 3A, B).

Ambulatory legs not distinctly elongated, dactyli slender (Figs 2A, C, 4A, C); second pair longest, last pair shortest (Figs 2A, C, 4A, C). Outer surface of merus weakly rugose, dorsal margin weakly serrated, without subdistal tooth, length ~ 4.1 × width (Figs 2A, 4A).

Male thoracic sternum smooth, weakly pitted; sternites 1/2 fused forming triangular structure; sternites 2/3 separated by deep but incomplete groove; sternites 3/4 completely fused; median longitudinal suture of sternites 7/8 deep (Figs 2C, 3C, E, 4C). Vulvae transversely ovate, widely located from each other, touching suture of sternites 5/6, posteromesial margin with low rim, opened obliquely upwards (Fig. 3F).

Male pleon broadly triangular; male telson relatively broad, lateral margins concave, width ~ 1.4 × length; male pleonal somite 6 trapezoidal, broad, width ~ 2.3 × length; somites 3-5 trapezoidal, gradually decreasing in width; somite 2 trapezoidal, reaching to bases of coxae of fourth ambulatory legs, thoracic sternite 8 not visible when pleon closed (Figs 2C, 3C, 4C). Female pleon ovate, covering most of thoracic sternum (Fig. 3D).

G1 slender, reaching pleonal locking tubercle in situ, with terminal and subterminal segments clearly demarcated (Figs 3E, H, I, 4D-G); subterminal segment stout, slightly sinuous (Figs 3H, I, 4D, E); terminal segment slender, relatively long, subconical, strongly sinuous, bent inwards, inner margin strongly concave, ~ 0.6 × length of subterminal segment, without groove for G2 on ventral side, tip rounded, dorsal flap absent (Figs 3H, I, 4D-G). G2 longer than G1; terminal segment relatively long; subterminal segment ~ 1.5 × length of terminal segment (Fig. 3J).

Colour in life.

Carapace and chelipeds are generally yellowish brown in mature individuals.

Habitat.

Parvuspotamon yuxiense can be found under rocks in hill streams at ~ 700-1000 m altitude.

Remarks.

Parvuspotamon yuxiense is the sole species of the genus and closely related to the species of Songpotamon gen. nov., and two species of Tenuipotamon Dai, 1990 ( Tenuipotamon yuxiense Chen, 1993, and Tenuipotamon xingpingense Chen, 1993) that are known from Xinping County, Yuxi City of Yunnan Province. Parvuspotamon yuxiense can nevertheless be differentiated from T. yuxiense and T. xingpingense by the following characters: anterolateral margins of the carapace entire and smooth (vs cristate); and G1 terminal segment relatively less strongly curved, lacking a dorsal flap (vs more strongly curved, with a distinct dorsal flap) [cf. Chen 1993: figs 3 (4-6), 4 (4-6)]. On the other hand, P. yuxiense can be differentiated from the species of Songpotamon gen. nov. by the characters in the carapace, vulvae and G1 (see Remarks for Songpotamon gen. nov.).

Geographic distribution.

Parvuspotamon yuxiense is known only from the Yuxi City, Yunnan Province, southwest China.