Pelodiscus sinensis

(Wiegmann, 1835)
Chinese softshell turtle

There is a marginal ridge on the oval, slightly longer than wide, carapace (to 25 cm). Juveniles exhibit longitudinal rows of blunt tubercles, but the adult carapace is smooth, except for one to a few enlarged, blunt knobs on the anterior rim above the neck. No preneural bone is present and only a single neural bone separates the anterior of the eight pairs of costals. The 8th costals meet at the midline. Carapacial bones are finely pitted. The carapace is olive to gray and in juveniles is patterned with round, light-bordered black spots. The white to yellow plastron is immaculate in adults but has large black blotches in juveniles. Callosities, totaling seven, occur on the hyo- and hypoplastra, the xiphiplastra, and sometimes the epiplastra. The epiplastra are separated, and the entoplastron forms obtuse angles to the midline. There is usually a suture between hyo- and hypoplastra. The skull is of moderate size with a bony snout which is longer than the greatest diameter of the orbit. The mandible lacks a symphysial ridge, and the width of the symphysis is greater than the greatest diameter of the orbit. Head and limbs are olive to yellowish white, and the head and neck may have fine black lines. The throat is either light with vermiculations or dark with yellow spots. There often are fine black lines radiating from the eyes. The tubular snout has a lateral ridge projecting from each side of the nasal septum; the lips are fleshy and the jaws are sharp.
The 66 chromosomes that compose the karyotype are as follows: 16 macrochromosomes (8 metacentric, 2 submetacentric, 4 acrocentric, 2 subtelocentric) and 50 microchromosomes (Bickham et al., 1983). Oguma (1937) reported 64 diploid chromosomes in males (12 macrochromosomes, 52 microchromosomes) and 63 in females; however, several chromosomes were probably lost during preparation.
Males differ from females in being shallower and having long, thick tails, with the vent near the tip. Females are more domed, and their tails barely extend past the carapacial rim.

Pelodiscus sinensis inhabits extreme southeastern Siberia (between the Ussuri and the Amur River drainages), adjacent Korea, central and southern China, Vietnam, and the islands of Hainan and Taiwan. It has been introduced into the Hawaiian Islands, Guam, one of the Mariana Islands, one of the Bonin Islands, Timor, and Japan.
The species is apparently the rarer of the two softshells introduced into the Hawaiian Islands, where it seems to be restricted to Kauai (McKeown and Webb, 1982). Studies by Sato et al. (1997) have revealed that the Chinese softshells on some of the islands in Okinawa Prefecture, southwestern Japan originated in Taiwan.

Geographic Variation
Pelodiscus sinensis is an extremely variable species with a wide distribution. Consequently, numerous taxa have been described from different parts of the species' range. Most recently described or resurrected are Trionyx axenaria Zhou et al., 1991 (synonymized with P. sinensis by Zhao, 1997); Trionyx maackii Brandt, 1857 (resurrected by Chkhikvadze, 1987); and Pelodiscus parviformis Tang, 1997. Some of these taxa may prove to be valid in thefuture, but until a complete [l][m]Glossary[/m][r]taxon[/r]taxonomic review of this complex is undertaken, it seems best to consider them synonyms of Pelodiscus sinensis.
The level of subspeciation may never be understood due to the vast quantities of individuals that have been shipped from many different localities to distant lands for the food trade, and because of the large scale farming operations with mixed genetic stock originating from different geographic sources.

In China, Pelodiscus sinensis is found in rivers, lakes, ponds, canals, and creeks with slow currents (Pope, 1935). On Kauai, Hawaii, it occurs in marshes and drainage ditches. The basking habit is not well-developed.

Natural History
Sexual maturity is reached in 4-6 years (Fukada, 1965; Yun et al., 1984). Spermatogenesis begins in May, and sperm production continues through July. Spermiogenesis becomes more prominent in September, and by October the germinal epithelium of the seminiferous tubules is mainly composed of spermatids and spermatozoa. Many spermatozoa also crowd the lumen at this time. The spermatozoa pass to the epididymides from November to February (Lofts and Tsui, 1977; Licht, 1982). Viable sperm may be retained in the female oviducts for almost a year after copulation (Yun et al., 1984).
Mating takes place from May to July in Japan (Fukada, 1965). The copulatory act occurs at the surface or underwater with the male holding the female's carapace with his forelimbs and sometimes biting at her head, neck, and limbs.
In Japan, nesting begins in late May and continues to mid-August (Mitsukuri, 1905). Licent (in Pope, 1935) discovered quantities of eggs on 14 June in southeastern Kansu, China. The nest is a squarish hole with the corners rounded out; it generally is about 7.5-10 cm across the entrance.
Females may ovulate 2-5 times a year, laying 8-12 to 20-30 eggs each time (Fukada, 1965; Yun et al., 1984). The white, spherical eggs average about 20 mm in diameter, but may be as large as 24 mm. Incubation takes about 60 (23-83) days, depending on soil tempareture.
Hatchlings average 27 mm in carapace length and are about 25 mm wide. The carapace is olive, and it may have a pattern of small, dark-bordered ocelli. Its marginal fold is prominent, as are the longitudinal rows of spiny tubercles. The plastron is orange-red, with (or occasionally without) large dark blotches. Limbs and head are olive above and lighter below; the hindlegs are orange-red below. The head has dark flecks, and dark lines radiate from the eyes. The throat is mottled, and the lips may have small, dark bars. There is a pair of dark blotches in front of the tail and a black band on the posterior side of each thigh.
Pelodiscus sinensis is predominantly carnivorous. Heude (in Pope, 1935) found the remains of fish, crustaceans, mollusks, insects, and seeds of marsh plants in stomachs he examined. Mitsukuri (1905) reported that juveniles feed on fish and that adults eat fish and bivalves. Captives eat canned and fresh fish, canned dog food, raw beef, mice, frogs, and chicken.

The genera Pelodiscus, Palea, and Dogania are closely related (Meylan, 1987).

IUCN Red List Status (1996)
Not listed.