Semicirculara, Chu & Wang & Sun, 2018

Chu, Kelin, Wang, Pengfei & Sun, Hongying, 2018, A new genus and species of primary freshwater crab and a new species of Artopotamon Dai & Chen, 1985 (Crustacea, Brachyura, Potamidae) from western Yunnan, China, Zootaxa 4422 (1), pp. 115-131 : 117-118

Semicirculara gen. nov.

Diagnosis. Carapace about 1.3 times broader than long, dorsal surface strongly convex longitudinally and transversely ( Fig. 2A ); cervical groove indistinct, H-shaped groove between gastric, cardiac regions distinct. Third maxilliped exopod without flagellum ( Fig. 3B ). Male pleon triangular, sixth somite width 2.2 times length; telson triangular, tip rounded, with proximal width 1.1–1.2 times length ( Fig. 4B ). G1 long, tip of terminal segment reaching suture between thoracic sternites 4, 5 in situ ( Fig. 4A ); subterminal segment 1.7 times as long as terminal segment ( Fig. 3C ; 5A); terminal segment slightly elongated inward ( Fig. 3D ; 5A), distal part of terminal segment elongated with ventrally directed semicircular lobe ( Fig. 3D ; 5A; 10A, B). Female vulvae partially exposed anteriorly to the thoracic sternites 5, 6 in situ, ovate, deep, posteromesial margin with a law raised rim, opened inward ( Fig. 4D ).

Type species. Semicirculara lincangensis sp. nov., by present designation.

Etymology. The genus name is derived from the Latin, semicircularis, which describes the G1 terminal segment, which has a ventrally directed semicircular lobe, as seen in the type species for the genus. Gender feminine.

Remarks. The new genus, Semicirculara , is morphologically most similar to Pararanguna Dai & Chen, 1985 , and Aparapotamon Dai & Chen, 1985 , as they share the following characters: the dorsal surface of the carapace is strongly convex longitudinally and transversely, the third maxilliped exopod is without a flagellum, the tip of the G1 terminal segment reaches beyond the sternal press-button in situ. But Semicirculara gen. nov. can be differentiated from Pararanguna by the G1 terminal segment being slightly elongated inward, and the distal part of terminal segment being elongated with a ventrally directed semicircular lobe ( Fig. 3C, D ; 5A) (versus G1 terminal segment ventral flap with semicircular protrusion, distal part of terminal segment elongated with a triangular lobe; Fig. 5B ; cf. Dai, 1999: fig. 200 (4, 5)) (also Table 1); and by having the female vulvae ovate, opened inward, and posterointernally bordered by a low, nearly flat margin ( Fig. 4D ) (versus female vulvae subcircular, posterointernally bordered by a distinctly raised margin; Fig. 4F ; cf. Dai, 1999: fig. 200 (8)) (also Table 1). Semicirculara gen. nov. can be differentiated from Aparapotamon by having the G1 subterminal segment about 1.7 times as long as terminal segment; terminal segment slightly elongated inward ( Fig. 3C, D , 5A ), distal part of terminal segment elongated with a ventrally directed semicircular lobe ( Fig. 3D ; 5A) (versus G1 subterminal segment about 1.3 times as long as terminal segment; distal part of terminal segment curved dorsally and inward, dorsal flap convex as discoid shape; Fig. 5C ; cf. Dai, 1999: fig. 196 (4, 5)) (also Table 1); and by having the female vulvae seemingly placed between thoracic sternites 5 and 6 in situ, opening inward, and with the posteromesial margin having a low rim ( Fig. 4D ) (versus female vulvae fully on thoracic sternite 6, posterolaterally bordered by a distinctly raised margin; Fig. 4E ; cf. Dai, 1999: fig. 195 (8)) (also Table 1).

1cf. Dai 1999: pl. 371; fig. 200. 2cf. Dai 1999: pl. 363; fig. 196.

Figures

FIGURE 2. Semicirculara lincangensis gen. & sp. nov., holotype, male, 18.8 ×14.4 mm, NNU 160562. A, dorsal view; B, frontal view of cephalothorax; C, ventral view of pleon.

FIGURE 3. Semicirculara lincangensis gen. & sp. nov., holotype, male, 18.8 × 14.4 mm, NNU 160562. A, outer surfaces of right major chela; B, left third maxilliped; C–D, left G1 without G2: D, dorsal view; E, ventral view of terminal segment; E, left G2. Scale bar = 1.0 mm.

FIGURE 4. A–D, Semicirculara lincangensis gen. & sp. nov. A, B, holotype, male, 18.8 × 14.4 mm, NNU 160562: A, sternopleonal cavity with right G1 in situ; B pleon; C, D, paratype, female, 20.2 × 15.9 mm, NNU 160567: C, pleon; D, thoracic sternum and vulvae. E, Pararanguna semilunatum (Dai & Chen, 1985): female, 22.3 × 17.1 mm, NNU 151103; thoracic sternum and vulvae. F, Aparapotamon inflomanum Dai & Chen, 1985: female, 21.6 × 17.9 mm, NNU 142202; thoracic sternum and vulvae. Scale bar = 1.0 mm.

FIGURE 5. Ventral view of G1. A, Semicirculara lincangensis gen. & sp. nov. holotype, male, 18.8 × 14.4 mm, NNU 160562. B, Pararanguna semilunatum (Dai & Chen, 1985) male, 16.9 × 13.3 mm, NNU151005. Scale bar = 1.0 mm. C, Aparapotamon inflomanum Dai & Chen, 1985, male, 16.8 × 13.6 mm, NNU 142201. Scale bar = 1.0 mm.