Pelodiscus shipian, Gong & Fritz & Vamberger & Gao & Farkas, 2022

Gong, Shiping, Fritz, Uwe, Vamberger, Melita, Gao, Yangchun & Farkas, Balázs, 2022, Disentangling the Pelodiscus axenaria complex, with the description of a new Chinese species and neotype designation for P. axenaria (Zhou, Zhang & Fang, 1991), Zootaxa 5125 (2), pp. 131-143 : 134-141

Pelodiscus shipian sp. nov.

( Figs. 4–6 )

Suggested English name: Chinese stone slab soft-shelled turtle

Suggested Chinese name: 石片Dz (shi pian bie)

Holotype. Jinan University , Guangzhou : JNU 20190011 , adult female preserved in alcohol, Liaohe River, Fengxin County, Jiangxi Province, China (28°43’N, 115°25’E), leg. Shiping Gong, 18 June 2019, European Nucleotide Archive ( ENA) accession numbers for DNA sequences: cyt b — OW235712 , P26S4— OW235765 , R35 — OW237755 .

Paratypes. Jinan University, Guangzhou: JNU 20190001–20190010 , ten adult males preserved in alcohol , same data as the holotype; JNU 20190012–20190017 , six adult females preserved in alcohol , same data as the holotype; JNU 20190019–20190022 , four adult females preserved in alcohol , same data as the holotype; JNU 20190023 , adult male preserved in alcohol , same data as the holotype; JNU 20190024 , adult female preserved in alcohol , same data as the holotype; JNU 20210002 , 20210003 , two adult females preserved in alcohol, Shaoyang County , Hunan Province, China, leg. Shiping Gong, 7 May 2021; JNU 20210004 , adult male preserved in alcohol, Taoyuan County , Hunan Province, China, leg. Shiping Gong, 7 May 2021; JNU 20210005 , adult male preserved in alcohol, Yongzhou City , Hunan Province, China, leg. Shiping Gong, 7 May 2021; JNU 20210006 adult female preserved in alcohol, Yongzhou City , Hunan Province, China, leg. Shiping Gong, 7 May 2021. ENA accession numbers of the paratypes are for cyt b sequences: OW235702 – OW235711 , OW235713 – OW235724 , OW235726 – OW235730 ; for P26S4 sequences: OW235762 – OW235764 , OW235766 – OW235772 , OW235774 , OW235775 ; for R35 sequences: OW237747 – OW237754 , OW237756 , OW237757 , OW237760 – OW237762 ; and for TB01 sequences: OW235731 – OW235753 , OW235756 – OW235761 .

Diagnosis. Besides its genetic distinctiveness ( Gong et al. 2018), Pelodiscus shipian sp. nov. differs from its congeners by the following combination of characters: (1) small adult size, <15 cm CL; (2) carapace distinctly keeled, more or less strongly tuberculated, usually olive clay-coloured and adorned with greenish black marbling but sometimes much darker with obscure pattern; (3) plastron yellowish white, typically immaculate except for a blurred-edged blotch behind each axilla that does not extend to the entoplastron and a slight black suffusion along its anterior border; (4) underside of the leathery margin with varying amounts of dark pigmentation; (5) head olive clay-coloured with numerous black splotches; (6) chin grey brown with pale stipples, throat dark grey, finely spotted with black; (7) neck with a wide yellow lateral band stretching from the ear backwards, which tends to fade with age; (8) entoplastron boomerang-shaped, the amount of bending of the transverse bar between the two posteriolaterally directed rami>90°.

Pelodiscus shipian sp. nov. cannot be confused with any other species of Pelodiscus except for P. axenaria and, perhaps, P. huangshanensis , its closest relatives constituting the P. axenaria complex, which both have a dark chin and throat finely stippled with black or an indistinct paler colour. The remaining species ( P. maackii , P. parviformis , P. sinensis , and P. variegatus ) have a light grey chin and throat with white spots or larger white markings that are either or not edged with a darker colour. For additional features see Farkas et al. (2019: Table 4).

Pelodiscus shipian sp. nov. differs from P. axenaria by having (1) a smaller adult size of <15 cm CL (vs.>15 CL); (2) no plastral markings except, rarely, relatively small fuzzy-edged blotches behind the axillae and a slight black suffusion on the forelobe (vs. a dark grey central blotch usually present and blotches behind the axillae extending to the entoplastron); (3) usually unmarked inner thighs (vs. thighs usually carrying well-defined, rarely indistinct, black markings on either side of the tail); and (4) a head and snout with numerous black splotches but without clearly discernible pre-, sub- and postocular stripes (vs. a head with fine black specks and streaks and thin, incomplete pre-, sub- and postocular stripes).

Pelodiscus shipian sp. nov. differs from P. huangshanensis by having (1) a larger adult size of> 12 cm CL (vs. <12 cm CL); (2) a rough, finely tuberculated carapace (vs. smooth carapace with tuberculation confined to the anterior edge and the leathery margin); (3) a distinctly marbled carapace pattern (vs. an olive brown to dark brown carapace without pattern); and (4) a more or less contrasting yellow lateral band on either side of the neck (vs. no lateral bands on neck when fully grown).

In the cyt b gene, a frequently used marker for estimating interspecific divergence in turtles (e.g., Kindler et al. 2012; Iverson et al. 2013), P. shipian sp. nov. differs from other Pelodiscus species on average by 5.30–7.53% ( Table 1 ). These values resemble those as observed between species of another softshell turtle genus ( Nilssonia ; Praschag et al. 2007).

Description of the holotype. Carapace length (CL) 100.5 mm, carapace width (CW) 88.1 mm, plastron length (PL) 74.4 mm, head width (HW) 19.8 mm, eye diameter 6.6 mm, interorbital distance 4.1 mm, snout length (SL) 8.9 mm. Carapace oval, slightly domed but with a strong median keel, widest at level of the posterior buttress spurs of the hypoplastra. Marginal ridge low, central tubercle indistinct. Dorsal surface roughened by longitudinal ridging and smaller protuberances spread over the leathery margin. The olive clay-coloured carapace is adorned with an extremely complex greenish black pattern consisting of reticulations and stellate spots, some enclosed by incomplete rings of the same colour, that give it a marbled appearance. Even though the reticulations extend roughly from the outer (pleural) sutures of the neurals laterally and posteriorly to the periphery of the shell, the two halves of the “saddle” are interconnected by several blotches across the vertebral line. Black stellate spots are scattered over the carapace but are well camouflaged in their heavily patterned surroundings. Entoplastron boomerang-shaped, the amount of bending of the transverse bar between the two posteriolaterally directed rami>90°. Callosities are small and present on the ento-, hyo-hypo- and xiphiplastra. Ventral surfaces are yellowish white suffused with cream yellow on the extremities and the leathery margin. Bridge and underside of leathery margin bear some vague bruise-like grey marks that are best defined along the shell borders. Fore- and hindfeet are well-webbed, having five digits each, with claws on the first three digits only. Each forelimb with four antebranchial scales, three of them free-edged. Each hindlimb with two horny scales, one smooth on the posterodorsal surface while the other, which is free-edged, is located on the posteroventral surface. Tail short, barely extending beyond the rear margin of the carapace and indicating the female gender of the specimen. Head extended to posterior level of eyes, terminating in flexible snout. Jaws closed, each covered by fleshy lips except anteriorly where the horny beaks are exposed. Top of head and snout with black splotches on an olive clay-coloured ground. Pre-, sub- and postocular stripes are thick but incomplete, not well discernible among the other markings. The chin is grey brown with pale stipples, the throat dark grey, finely spotted with black; lips are olive clay-coloured with yellow and black dappling.

Variation. CL ranges from 74.1 mm to 103.2 mm, PL from 54.6 mm to 76.5 mm in our type series consisting of 28 specimens. Measurements are given in Table 2 . Males have a proportionally bulkier head (PL/HW = 3.37–3.99, mean = 3.60 in males, 3.18–4.20, mean = 3.77 in females; HW/SL = 1.80–2.30, mean = 2.00 in males, 1.69–2.44, mean = 1.95 in females) as well as a much longer and thicker tail. Sexual dimorphism is clearly apparent at a PL of 54.6 mm (JNU 20190010) or possibly even earlier. However, it is presently unknown at what size sexual maturity is reached in this species. According to our data, the two genders may attain similar sizes in Pelodiscus shipian sp. nov., unlike in P. axenaria , in which males seem to grow larger than females ( Zhou et al. 1991; S. Gong pers. obs.).

Pattern intensity varies considerably in Pelodiscus shipian sp. nov. Whereas the carapace of some individuals, such as the holotype (JNU 20190011; 74.4 mm PL) and one paratype (JNU 20190013; 64 mm PL), both females, has a decidedly marbled appearance, the pattern bears a more striking resemblance to leaf camouflage with more conspicuous stellate spots in others (e.g., paratypes JNU 20190001, 20190007, males; JNU 20190016, 20190017, 20210006, females) or is almost imperceptible due to a general darkening of the ground colour (e.g., JNU 20190002, 20190004, 20190008, 20190010, males; JNU 201900012, 20190019, females); see Figure 6 for examples. The plastron is typically unmarked except for some colour suffusion resembling bruising along its anterior perimeter and relatively small fuzzy-edged blotches behind the axillae. However, these markings may occasionally extend medially, covering much of the plastral forelobe but never actually contacting the entoplastron (JNU 201900005, male; JNU 201900012, 201900017, both females). The black markings on either side of the tail typical for P. axenaria are absent in P. shipian sp. nov., but melanistic specimens may display some dark pigmentation on their thighs (e.g., JNU 201900005, male; JNU 201900012, 20210006, both females). Two examples are shown in Figure 6 . The lateral bands on the neck are bright yellow in smaller specimens, particularly males (e.g., JNU 201900010), and lose definition with increasing age/size but usually remain discernible in both sexes.

Distribution. The exact geographical range of Pelodiscus shipian sp. nov. is unknown at present. Apart from the type locality, the Liaohe River in Fengxin County, Jiangxi, specimens have been obtained in the counties of Shaoyang and Taoyuan and the City of Yongzhou (Hunan Province), suggesting sympatry or confusion with P. axenaria .

Originally, the distribution range of P. axenaria was believed to encompass the counties and cities of Taoyuan, Pingjiang, Rucheng, Lingling, and Shaoyang in Hunan Province, China ( Zhou et al. 1991). However, all specimens that we could obtain from Taoyuan and Shaoyang Counties are P. shipian (see our paratype series); our neotype of P. axenaria comes from Tongdao County in Hunan Province. The records from Zhou et al. (1991) were not genetically verified, so that we cannot exclude that some of them referred to P. shipian . However, genetically verified records of P. axenaria ( Chen et al. 2005, 2006; Yang et al. 2011; Gong et al. 2018) are known from Shaoguan (Guangdong), Longsheng and Quanzhou (Guangxi) and from Changde and Anren (Hunan). This suggests that P. axenaria and P. shipian at least occur in closest proximity, if not in sympatry, in Hunan ( Fig. 7 ).

Another small-bodied Pelodiscus species, P. parviformis , was described from Guangxi and Hunan ( Tang 1997). Pelodiscus parviformis is morphologically and genetically distinctive ( Gong et al. 2018; Farkas et al. 2019). Nevertheless, it is possible that some genetically unconfirmed records for P. parviformis refer to P. axenaria or P. shipian .

Our map ( Fig. 7 ) collates for the P. axenaria complex the currently known genetically verified records.

Etymology. The name ‘ shipian’ is the romanisation of 石片 (shi pian, Chinese for “slab”), derived from the local (Fengxin, Jiangxi) name of the species 石片Dz (shi pian bie = stone slab soft-shelled turtle) that alludes to its resemblance to a flat stone. The suggested English common name refers to the same feature. The scientific species name is used as a noun in the nominative singular in apposition to the generic name (ICZN 1999: Article 11.9.1.2).

Figures

FIGURE 4. Dorsal and ventral aspects of the holotype of Pelodiscus shipian sp. nov. (JNU 20190011, adult female, 100.5 mm CL).

FIGURE 5. One of the paratypes of Pelodiscus shipian sp. nov. (JNU 20210002, adult female, 88.2 mm CL) in life.

FIGURE 6. Variation in colouration and pattern in Pelodiscus shipian sp. nov. Freshly dead paratypes JNU 20210005 (male, top and bottom left), JNU 20210004 (male, top right) and JNU 20210006 (female, bottom right), all from Hunan Province, China. Not to scale.

FIGURE 7. Genetically verified records for species of the Pelodiscus axenaria complex in central China (compiled from Chen et al. 2005, 2006; Yang et al. 2011; Gong et al. 2018, 2021 and this study). Blue: P. axenaria, red: P. huangshanensis, green: P. shipian sp. nov.