Longpotamon, Shih, Hsi-Te, Huang, Chao & Ng, Peter K. L., 2016

Shih, Hsi-Te, Huang, Chao & Ng, Peter K. L., 2016, A re-appraisal of the widely-distributed freshwater crab genus Sinopotamon Bott, 1967, from China, with establishment of a new genus (Crustacea: Decapoda: Potamidae), Zootaxa 4138 (2), pp. 309-331 : 318-325

Longpotamon gen. nov.

( Figs. 6–9 ; 10C–F, 11)

Type species. Sinopotamon exiguum Dai, 1997 ( Figs. 6 , 7 , 10 C, D), by present designation.

Diagnosis. Carapace ( Fig. 6 ) broader than long; with convex dorsal surface, surface generally smooth; postorbital, epigastric cristae distinct, not confluent; external orbital angle broadly triangular, separated from anterolateral margin by narrow to almost undiscernible gap; median lobe of posterior margin of epistome broadly triangular; third maxilliped with rectangular ischium, exopod of third maxilliped reaching beyond anterior edge of ischium, with well-developed flagellum; male abdomen triangular, with telson subtriangular with relatively less concave lateral margins; G1 ( Figs. 7–9 ) generally straight, not reaching tubercle of abdominal lock, terminal segment pointed upwards to inwards, flap of subterminal segment extending out subdistally; basal segment of G2 subrectangular. Vulva ( Figs. 10 C–F, 11) relatively smaller, shallow, not reaching to suture of sternites 5, 6.

Etymology. The prefix Long means "Dragon" in Chinese. It is an iconic symbol of the Chinese people and their culture. The word long also implies the main distribution of this genus, which is along the drainage of Chang Jiang (= Yangtze River), which literally means the "Long River". The name is an arbitrary combination of long with Potamon ; gender neuter.

Distribution. The distribution of Longpotamon gen. nov. encompasses that of Sinopotamon s. str. ( Fig. 13 ; Shih & Ng 2011: fig. 7; see Discussion); spanning the drainage of the Yangtze River and extending north to the drainage of Yellow River and south to the eastern side of Wuyishan Range ( Fig. 13 ).

Remarks. With the transfer of the bulk of Sinopotamon species to Longpotamon gen. nov., the latter now becomes the most diverse genus of Chinese freshwater crabs, with 73 species (cf. Ng et al. 2008; Shih & Ng 2011).

Sinopotamon exiguum Dai, 1997 ( Figs. 6 , 7 , 10 C, D) is here selected as the type species of Longpotamon gen. nov. It is noteworthy that this species is also sympatric with Sinopotamon davidi , the type species of Sinopotamon s. str., which suggests that there may be morphological, chemotatic, or behavioral factors that reduce or prevent resource competition and/or hybridization ( Brown & Wilson 1956; Pfennig & Pfennig 2009).

The external morphology between Longpotamon gen. nov. and Sinopotamon is strikingly similar, with marked differences only in the G1 and vulva. The G1 is the most reliable character in separating the two genera, with Longpotamon gen. nov. having a short G1 that does not exceed the tubercle of the abdominal lock on thoracic sternite 5 ( Figs. 7 A, 8, 9) (in contrast to a long G1 that overreaches the tubercle of the abdominal lock in Sinopotamon , Figs. 4 A, 5), a short G1 terminal article ( Fig. 7 B–E) (long G1 terminal article in Sinopotamon , Fig. 4 B–E), a G1 that points inward towards the median part of the thoracic sternum then upward towards the buccal cavity ( Figs. 7 A, 8, 9) (G1 that points outward then inward in Sinopotamon , Figs. 4 A, 5), and a flap of G1 subterminal segment that extends outwards subdistally ( Figs. 7 A, 8, 9) (flap of G1 subterminal segment that extends outward medially in Sinopotamon , Figs. 4 A, 5). The structures of the vulvae are also different, with the vulva of Longpotamon gen. nov. being small and shallow that does not reach the suture of sternites 5 and 6 ( Fig. 11 ) (large and deep vulva that does reach sternal suture 5, 6 in Sinopotamon ; Fig. 10 ).

Other useful characters include the orbit size ( Figs. 1 B, 3B, 6B), being relatively wider in Longpotamon gen. nov. (narrower in Sinopotamon ), and the shape of the male telson ( Figs. 1 C, 3C, 6C), which is subtriangular in Longpotamon gen. nov. (more elongated in Sinopotamon , with prominently concave lateral margins). Both Sinopotamon and Longpotamon gen. nov. are large species, with an adult size of CW 50 mm and above ( Dai 1999), e.g., S. davidi (CW 50.3 mm), S. fuxingense (CW 58.2 mm), L. longlinense (Dai, 1997) (CW 53.2 mm) and L. rongshuiense (Dai, 1995) (CW 51.0 mm). In our study, the largest CW of S. davidi and S. exiguum is 67.2 mm and 64.7 mm, respectively.

Mediapotamon is superficially similar to Longpotamon gen. nov., but its square carapace (broad in Sinopotamon ), cylindrical-shaped tip of G1 (compressed tip in Sinopotamon ), and subquadrate base of G2 (subrectangular in Sinopotamon ) immediately set them apart. The adult size of Mediapotamon is also smaller (adult size rarely exceeding CW 20 mm) than either Longpotamon gen. nov. and Sinopotamon (cf. Dai 1999).

Figures

FIGURE 1. Sinopotamon davidi (Rathbun, 1904), Ƌ, CW 45.5 mm, lectotype, MNHN-IU- 2014 - 8620. A, dorsal view; B, frontal view; C, ventral view.

FIGURE 4. Sinopotamon davidi (Rathbun, 1904), Ƌ (CW 67.2 mm), NCHUZOOL 13648. A, ventral view showing the natural position of G 1, and tubercles of abdominal lock (arrowed); B – E, right G 1 s; B, dorsal view; C, dorsal view of terminal segment; D, ventral view; E, ventral view of terminal segment.

FIGURE 6. Longpotamon exiguum (Dai, 1997), Ƌ (CW 64.7 mm), NCHUZOOL 13921. A, dorsal view; B, frontal view; C, ventral view.

FIGURE 7. Longpotamon exiguum (Dai, 1997), Ƌ. A, CW 64.7 mm, NCHUZOOL 13921, ventral view showing the natural position of G 1 s, and tubercles of abdominal lock (arrowed); B – E, CW 59.6 mm, NCHUZOOL 13921, right G 1; B, dorsal view; C, dorsal view of terminal segment; D, ventral view; E, ventral view of terminal segment.

FIGURE 8. Natural position of male G 1 s and tubercles of abdominal lock (arrowed) of species of Longpotamon. A, L. decrescentum, CW 48.5 mm, CAS CB 11314; B, L. denticulatum, CW 38.9 mm, CAS CB 05855; C, L. honanense, CW 39.6 mm, CAS CB 07135; D, L. jixiense, CW 34.3 mm, CAS CB 07621; E, L. kenliense, holotype, CW 46.8 mm, CAS CB 00334; F, L. parvum, holotype, CW 24.6 mm, CAS CB 00367; G, L. shaoyangense, CW 31.2 mm, CAS CB 08588; H, L. siguqiaoense, CW 33.9 mm, CAS CB 09224; I, L. styxum, CW 44.4 mm, CAS CB 08770.

FIGURE 9. Natural position of male G 1 s and tubercles of abdominal lock (arrowed) of species of Longpotamon gen. nov.. A, L. xingshanense, CW 43.9 mm, CAS CB 10607; B, L. xiushuiense, CW 33.4 mm, CAS CB 09754; C, L. yixianense, CW 40.6 mm, CAS CB 11286; D, L. teritisum, paratype, CW 39.6 mm, CAS CB 00426; E, L. turgidum, CW 38.4 mm, CAS CB 09082; F, L. xiangxiense, CW 39.3 mm, CAS CB 10153.

FIGURE 10. Vulvae of species of Sinopotamon (A, B) and Longpotamon gen. nov. (C – F). A, S. davidi, CW 50.8 mm, NCHUZOOL 13913; B, S. yaanese, CW 20.5 mm, NCHUZOOL 13915; C, L. exiguum, CW 29.2 mm, NCHUZOOL 13922; D, L. exiguum, CW 40.3 mm, NCHUZOOL 13923; E, L. baiyanense, CW 37.5 mm, NCHUZOOL 13919; F, L. jianglense, CW 33.5 mm, NCHUZOOL 13926.

FIGURE 11. Vulvae of species of Longpotamon, gen. nov.. A, L. loudiense, CW 32.3 mm, NCHUZOOL 13932; B, L. mindongense, CW 26.6 mm, NCHUZOOL 13930; C, L. shensiense, CW 34.0 mm, NCHUZOOL 13933; D, L. tongbaiense, CW 46.1 mm, NCHUZOOL 13934; E, L. sp. 1, CW 41.5 mm, NCHUZOOL 13935; F, L. sp. 3, CW 31.3 mm, NCHUZOOL 13936.

FIGURE 13. Updated distribution of the genera Sinopotamon and Longpotamon gen. nov. (modified from Shih & Ng 2011). The red dotted line represents the recorded range of Sinopotamon, with circles for species mainly in Sichuan, triangles for species from Guizhou, and squares for species from Hubei (data from Dai 1999 and this study). Solid purple line represents the range for Longpotamon gen. nov.