Genus Songpotamon gen. nov.

Figs 5, 6, 7, 8, 9, 10

Type species.

Songpotamon funingense sp. nov., by present designation.

Species included.

Songpotamon dixuense (Naruse, Chia & Zhou, 2018), comb. nov., Songpotamon funingense gen. et sp. nov., and Songpotamon malipoense gen. et sp. nov.

Diagnosis.

Medium sized (adult carapace width 19-27 mm, n = 16). Carapace broader than long, ovate; dorsal surface convex, generally smooth, pitted, regions not clear; branchial regions swollen (Figs 5A, 7A). Postorbital and epigastric cristae not confluent, separated by shallow groove (Figs 5A, 7A). External orbital angle bluntly triangular, outer margin separated from anterolateral margin of carapace by shallow cleft (Figs 5A, 7A). Anterolateral margin of carapace convex (Figs 5A, 7A). Orbits large; supraorbital and infraorbital margins smooth (Figs 5B, 7B). Exopod of third maxilliped reaching beyond anterolateral corner of ischium, without flagellum (Figs 6C, 8C). Thoracic sternites 3/4 in male fused except for incomplete groove demarcating suture (Figs 5C, 6E, G, 7C, 8E, G). Vulvae transversely ovate, relatively closely located to each other, touching suture of sternites 5/6 (Figs 6H, 8H). Male pleon narrowly triangular (Figs 5C, 6E, 7C, 8E). G1 slender, almost reaching or reaching beyond pleonal locking tubercle in situ (Figs 6G, 8G, 9A, B, D, E, 10A-D); terminal segment slender, subconical, bent outwards, relatively short, ~ 0.4 × length of subterminal segment, with distinct groove for G2 on ventral side, tip subtruncate, gently recurved upwards, dorsal flap absent (Figs 9A, B, D, E, 10A-D). G2 longer than G1; terminal segment relatively short; subterminal segment ~ 5 × length of terminal segment (Fig. 9C, F).

Etymology.

The genus is named after the late Prof. Daxiang Song, a senior academician in the Chinese Academy of Sciences, in the honour of his immense contributions to Chinese invertebrate systematics; in arbitrary combination with the genus name Potamon Savigny, 1816. Gender of genus neuter.

Remarks.

Songpotamon gen. nov. is established for S. dixuense comb. nov. and two new species, S. funingense sp. nov. and S. malipoense sp. nov. Songpotamon dixuense comb. nov. was previously in Parvuspotamon, but here transferred to Songpotamon gen. nov. because it possesses the key generic characters of the new genus, which includes, the medium body size (adult carapace width 19-27 mm), the third maxilliped exopod lacking a flagellum, the external orbital angle being bluntly triangular, the slender G1 shape, and the terminal segment being subconical and with a groove for G2 on the ventral side (cf. Naruse et al. 2018: figs 24-27).

Songpotamon gen. nov. can easily be distinguished from Parvuspotamon by the following characters: 1) carapace dorsal surface with scattered pits (Figs 5A, 7A; cf. Naruse et al. 2018: fig. 25A) (vs smooth; Figs 2A, 4A); 2) outer margin of the external orbital angle separated from the anterolateral margin of the carapace by the shallow cleft (Figs 5A, 7A; cf. Naruse et al. 2018: fig. 25A) (vs confluent with each other; Figs 2A, 4A); 3) vulvae relatively close located to each other (Figs 6H, 8H; cf. Naruse et al. 2018: fig. 27) (vs relatively widely located from each other; Fig. 3F); 4) G1 terminal segment relatively shorter, ~ 0.4 × the length of the subterminal segment, with a truncated tip (Figs 9A, B, D, E, 10A-D; cf. Naruse et al. 2018: fig. 26A-D) (vs relatively longer, ~ 0.6 × the length of the subterminal segment, with a rounded tip; Figs 3H, I, 4D-G); 5) G1 terminal segment bent outwards but with the tip gently recurved upwards, the inner margin being straight to gently curved (Figs 9A, B, D, E, 10A-D; cf. Naruse et al. 2018: fig. 26 A-D) (vs bent inwards, with the inner margin being strongly concave; Figs 3H, I, 4D-G); and 6) groove for G2 on the G1 terminal segment clearly visible in the ventral view (Figs 9 B, E, 10B, D; cf. Naruse et al. 2018: fig. 26A, B) (vs not visible; Figs 3I, 4E, G).

Furthermore, Songpotamon gen. nov. is most likely to be confused with Chinapotamon Dai & Naiyanetr, 1994, as both the genera have a very similar carapace physiognomy, and their G1 terminal segment is subconical, with the groove for G2 visible in the ventral view. The new genus, Songpotamon gen. nov., is nevertheless distinguished from Chinapotamon by the following characters: 1) carapace relatively high (Figs 5B, 7B) (vs relatively low); 2) ambulatory legs relatively stout (Figs 5A, C, 6D, 7A, C, 8D) (vs relatively slender); 3) anterolateral margin of the carapace being less convex (Figs 5A, 7A) (vs strongly convex); 4) third maxilliped exopod without flagellum (Figs 6C, 8C) (vs with well-developed flagellum); 5) thoracic sternites 3/4 with incomplete but distinct groove demarcating suture (Figs 5C, 6E, G, 7C, 8E, G) (vs groove demarcating suture absent); and 6) G1 terminal segment gently curved outwards (Figs 9A, B, D, E, 10A-D) (vs strongly bent outwards) (cf. Dai 1999: figs 42-47; Ng 2017: figs 2-4, 6-8; Zou et al. 2018: figs 2-6).

Geographic distribution.

Songpotamon gen. nov. is known from Wenshan Prefecture, eastern Yunnan Province, southwest China.