Pelodiscus axenaria ( Zhou, Zhang & Fang, 1991 )

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 : 132-134

Pelodiscus axenaria ( Zhou, Zhang & Fang, 1991)

( Figs. 1–3 )

Neotype. Jinan University , Guangzhou : JNU 20210001 , adult male preserved in alcohol, Yudai River, Tongdao County, Hunan Province, China (26°09’N, 109°46’E), leg. Shiping Gong, 25 May 2021; European Nucleotide Archive ( ENA) accession numbers for DNA sequences: cyt b — OW235725 , P26S4— OW235773 , R35 — OW237758 and OW237759 (two alleles), TB01— OW235754 and OW235755 (two alleles).

Description of the neotype. Carapace length (CL) 128.7 mm, carapace width (CW) 113.3 mm, plastron length (PL) 88.9 mm, head width (HW) 26.8 mm, eye diameter 7.6 mm, interorbital distance 3.9 mm, snout length (SL) 12.4 mm. Carapace oval, nearly circular in appearance, slightly domed but with a clear median keel, widest at level of the posterior buttress spurs of the hypoplastra. Marginal ridge low, central tubercle indistinct. Dorsal surface smooth except for the longitudinal ridging of the bony disk and some blunt, barely discernible protuberances spread over the leathery margin, mostly confined to the pelvic region. The olive clay-coloured carapace is suffused with dark grey and black, displaying an extremely complex blotched and mottled pattern that, to some extent, resembles bilaterally symmetrical inkblots. The reticulations extend roughly from the outer (pleural) sutures of the neurals side- and backwards to the periphery of the shell, with the two halves of the “saddle” being connected by a dark blotch, approximately at the level of neural 5. Jet black stellate spots are also present along the perimeter of the bony disk as well as the leathery margin but are not obvious due to their dark grey surroundings. The entoplastron is boomerang-shaped, the amount of bending of the transverse bar between the two posteriolaterally directed rami is>90°. Callosities are small and only present on the hyo-hypo- and xiphiplastra. Ventral surfaces are cream yellow to yellowish white, with distinct dark grey markings on both plastron and thighs. There is a blurred-edged patch between the anterior extensions of the epiplastra that breaks up into bruise-like suffusions along the anterior plastral margin and towards the entoplastron where it fades and does not contact the large central blotch covering the hyo-hypo- and xiphiplastra. There is an additional, even darker grey, fuzzy-edged blotch on both sides behind the axillae and continuing in the direction of, but not reaching, the hyoplastra. Bridge and underside of leathery margin with contusion-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 has four antebranchial scales, three of them free-edged. Each hindlimb has two horny scales, one smooth on the posterodorsal surface, while the other, which is free-edged, is located on the posteroventral surface. Extremities have a few scattered, very small dark spots on an olive clay-coloured background. Lower surfaces of the front legs are suffused with black, except for a patch just in front of the axillae. The inner thighs carry well-defined black markings on either side of the long and thick tail, which extends beyond the rear margin of the carapace, indicating the male gender of the specimen. Head fully extended, terminating in flexible snout. Jaws closed, each covered by fleshy lips except anteriorly where the horny beaks are exposed. Top of head with fine black specks and streaks on an olive clay-coloured ground. Pre-, sub- and postocular stripes thin and incomplete. The chin is grey brown with pale stipples, the throat dark, without any clear pattern. The lips are olive clay-coloured with light and dark flecks. There is a pale band on either side of the neck.

Remarks. Zhou et al. (1991) did not provide the etymology for the species epithet ‘ axenaria .’ It cannot be excluded that the name originated from a typographic misspelling of the Latin adjective arenaria (= sandy) and had been intended as an allusion to the Chinese vernacular name of the species (ḊDz sha bie = sand soft-shelled turtle). However, the epithet ‘ axenaria’ was generally accepted as a noun (of unknown meaning) in apposition, according to Article 31.1 of the International Code of Zoological Nomenclature (ICZN 1999) and we continue to do so for the sake of nomenclatural stability. Although Article 32.5 (ICZN 1999) would allow correction, we argue there is no clear evidence of an inadvertent error, especially in the light that the gender in the original combination with Trionyx should have been masculine (‘ Trionyx axenarius ’).

Figures

FIGURE 1. Dorsal and ventral aspects of the freshly dead neotype of Pelodiscus axenaria (JNU 20210001, adult male, 128.7 mm CL).

FIGURE 2. Neotype of Pelodiscus axenaria (JNU 20210001, adult male, 128.7 mm CL) in life.

FIGURE 3. Variation in plastron colouration and pattern in Pelodiscus axenaria. Males above, females below (none collected); all from Longsheng, Guangxi Zhuang Autonomous Region, China. Not to scale.