Sinopotamon Bott, 1967

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 : 312-318

Sinopotamon Bott, 1967

( Figs. 1–5 ; 10A, B)

Type species. Potamon (Potamon) davidi Rathbun, 1904 , by original designation.

Diagnosis. Carapace ( Figs. 1 , 3 ) 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 non-existent 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, telson relatively elongate with strongly concave lateral margins; G1 ( Figs. 2 A–C, 4, 5) generally straight, reaching beyond tubercle of abdominal lock, terminal segment pointed upwards to outwards, flap of subterminal segment extending out medially; basal segment of G2 subquadrate. Vulva ( Figs. 2 D, 10A, B) large, wide, deep, reaching to sternal suture 5, 6.

Distribution. Most species are found in the Sichuan Basin covering Sichuan Province and Chongqing City, extending to the border areas of the adjacent Shaanxi, Hubei, and Guizhou provinces ( Fig. 13 ).

Remarks. The revised Sinopotamon s. str. now contains 12 species: S. chishuiense Dai & Yuan, 1988 , S. cochlearidigitum Dai, Chen, Zhang & Lin, 1986 , S. davidi ( Rathbun, 1904) , S. ebieanense Huang, Luo & Liu, 1986 , S. emeiense Dai, 1990 , S. fuxingense Dai & Liu, 1994 , S. introdigitum Dai, Chen, Zhang & Lin, 1986 , S. kwanhsiense Tai & Sung, 1975 , S. pingshanense Dai & Liu, 1994 , S. weiyuanense Dai, Chen, Liu, Luo, Yi, Liu, Gu & Liu, 1990 , S. yaanense (Chung & Tsao, 1962) , and S. yichangense Dai, 1999 . Two of these species are atypical in possessing spoon-shaped tips of the chela: S. cochlearidigitum and S. introdigitum (cf. Dai 1999: figs. 174, 175), which may be an adaptation to feeding on algal and plant matter (e.g., as in the intertidal sesarmid Stelgistra: Ng & Liu 1999 ). Their key male and female morphological characters nevertheless agree with the generic features of the type species, S. davidi , and are thus retained in Sinopotamon s. str. Molecular studies may need to be undertaken to ascertain their position in the genus.

Rathbun (1904: 264) stated that she described Potamon (Potamon) davidi from 12 specimens: five males, two females, and five juveniles, from "Han-Tchong-Fou" (now Hanzhong City, Shaanxi Province). She gave measurements for two males (CW 33.3 mm, 45.5 mm) and one female (CW 38.0 mm) ( Rathbun 1904: 264). The collector was the famous French naturist, Jean Père Armand David (1826–1900), who stayed in the Hanzhong area in 1873 (see Jupp 2015). There are nine specimens of Potamon (Potamon) davidi in MNHN: 3 adult males (CW 23.1 mm, 25.7 mm, 45.5 mm) ( Figs. 1 , 2 ), 1 adult female (CW 37.8 mm), 2 young males (CW 16.0 mm, 16.4 mm), 1 young female (CW 18.8 mm), 1 juvenile (CW 15.8 mm), and one badly damaged specimen of undeterminable sex. The largest male (CW 45.5 mm; Figs. 1 , 2 A, B) only has the right G1 attached but no trace of the left G1. The catalogue number for the MNHN material is somewhat confusing. One of the labels in the bottle was hand-written with "Han-Tchong-Fou A. David 545.73", which was almost certainly David's station or specimen number. The original museum catalogue number is "BP 91" but it has recently been recatalogued under as "MNHN IU 2014- 8620". There are three additional specimens in USNM (USNM 29981) which Rathbun had retained during her study: 1 male (CW 33.3 mm), 1 female (CW 27.7 mm) and 1 juvenile (CW 15.8 mm). All are marked as " syntypes " collected in 1873. An additional male specimen was found in SMF (SMF 4504, CW 32.8 mm), marked as a " Paralectotypus ", is almost certainly among the specimens examined by Bott (1970: pl. 54, fig. 69). This would make for a total of 13 specimens, suggesting that when Rathbun (1904) described the species and listed 12 specimens, she did not include the crushed and badly damaged MNHN specimen.

In his material examined, Bott (1967: 206) wrote "Maße: 33:26:15: 10 mm. Locus typicus: China, Han- Tschong-Fu, 800 m. Material: Han-Tschong-Fu, Shensi, Central-China (1♂ Lectotypus, 3♂ 1♀ juv. Paratypoide MPa. 545-73)". His cited catalogue number "MPa. 545-73" is clearly a misinterpretation of David's field data. His drawing of the G1 ( Bott 1967: fig. 4) did not indicate from which specimen it was from. He repeated the same text in his later work (Bott 1970: 185) and his figure of the G1 (Bott 1970: pl. 40, fig. 68) and overall habitus (Bott 1970: pl. 54, fig. 69). The problem with Bott's data is that we do not know which specimen is the lectotype among the type series, although one male (SMF 4504) was labelled as a paralectotype. While he identified one male as the lectotype, he did not specifically give the size of this specimen, and he had a total of four males on hand. Although he gave the measurements for one specimen: CW 33 mm, CL 26 mm, he did not state its sex or specifically says that this was in fact his lectotype. The manner of his presentation makes it unclear which is the specimen. No male or female specimen among the MNHN material has measurements that come even close to Bott's data. Neither is there data nor label that says which was the specimen Bott chose as the lectotype. Only one male specimen, the largest CW 45.5 mm, as noted above, had the left G1 removed. Bott would have almost certainly have borrowed the largest male from MNHN and drawn its G1, and his figures of this structure are presumably from this specimen. From his text, Bott had borrowed only four males and a juvenile female from MNHN for his revision, not the complete series. There is no evidence he examined the USNM material. Regardless of the circumstances, Article 74.5 of the Code ( ICZN 1999) clearly states that "the author must have unambiguously selected a particular syntype to act as the unique name-bearing type of the taxon". As such, Bott's (1967, 1970) selection of a lectotype is invalid as his action was not "unambiguous". We here select the largest male in MNHN (CW 45.5 mm) ( Figs. 1 , 2 A, B) as the lectotype of Potamon (Potamon) davidi Rathbun, 1904 . This is necessary as we need to stabilize the taxonomy of the type species and genus, and more so considering we are describing a new genus here as well.

Dai (1975) examined S. davidi , S. yaanense , and S. kwanhsienense , and concluded their relationship is close because of the consistently straight and long G1, which is different from that in S. chekiangense Tai & Sung, 1975 . Dai (1999) divided Sinopotamon into several forms mainly based on the shape and direction of the G1 (cf. the key in Dai 1999: 199–205). In fact, the relative length of the G1 and the drawings of the natural position of the G1 provided in Dai's (1999) monograph help distinguish the generic affinities of the various species.

Species of Sinopotamon and Longpotamon can be distinguished by several morphological characters, which are discussed in the "Remarks" section for the new genus.

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 2. Sinopotamon davidi (Rathbun, 1904), MNHN-IU- 2014 - 8620. A – B, Ƌ, lectotype, CW 45.5 mm. A, ventral view showing the natural position of G 1 and tubercles of abdominal lock (arrowed); B, dorsal view of terminal segment of G 1; C, Ƌ, paralectotype, CW 25.7 mm, ventral view of terminal segments of G 1 and G 2; D, ♀, paralectotype, CW 37.8 mm, ventral view of abdomen, showing the vulvae (arrowed).

FIGURE 3. Sinopotamon davidi (Rathbun, 1904), Ƌ (CW 67.2 mm), NCHUZOOL 13648. 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 5. Natural position of male G 1 s and tubercles of abdominal lock (arrowed) of species of Sinopotamon. A, S. chishuiense Dai & Yuan, 1988, holotype, CW 30.9 mm, CAS CB 32; B, S. cochlearidigitum Dai, Chen, Zhang & Lin, 1986, CW 31.2 mm, CAS CB 5194; C, S. ebianense Huang, Luo & Liu, 1986, CW 31.8 mm, CAS CB 6429; D, S. emeiense Dai, 1990, holotype, CW 41.3 mm, CAS CB 127; E, S. fuxingense Dai & Liu, 1994, CW 54.1 mm, CAS CB 5561; F, S. introdigitum Dai, Chen, Zhang & Lin, 1986, CW 40.5 mm, CAS CB 11336; G, S. kwanhsiense Tai & Sung, 1975, CW 45.3 mm, CAS CB 7659; H, S. pingshanense Dai & Liu, 1994, holotype, CW 45.9 mm, CAS CB 379; I, S. yichangense Dai, 1999, CW 22.5 mm, CAS CB 11164.

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.