Mauremys japonica

(Temminck and Schlegel, 1835)
Japanese pond turtle

This is a Japanese semi-aquatic turtle with a posteriorly serrated brown carapace. Reaching a length of 18.2 cm, the carapace has a single low medial keel, is heavily serrated posteriorly, and also has a small posterior notch. Vertebrals are generally broader than long with the first broadest of all, and each carapacial scute bears growth annuli and well-marked, elevated radiations which diverge anteriorly from the block representing the original hatchling scute. Lateral marginals may be slightly upturned. Older individuals may have almost totally dark-brown carapaces, but those of younger turtles are olive to brown with some yellow along the vertebral keel and yellow and dark mottlings along the seam separating the pleurals and marginals. The brown to black plastron is flat, slightly upturned anteriorly, and has a wide posterior notch. The plastral formula is: abd > fem >< pect > an > gul > hum. The brown bridge is about as wide as the length of the posterior plastral lobe. The head is rather small and the upper jaw is neither hooked nor notched. The triturating surface of the upper jaw is narrow and lacks a ridge. The snout is only slightly projecting. Head skin is light brown, with dark spots on the jaws, chin, and sides. The neck is brown with a series of stripes on raised scales. Limbs and tail are dark brown with some light yellow on the outer border of the limbs and dorsal surface of the tail.
The karyotype is 2n = 52; 28 macrochromosomes (18 metacentric or submetacentric, 10 telocentric or subtelocentric) and 24 microchromosomes (Bickham and Carr, 1983).
The plastron of the male is only slightly concave, but the lateral margins of the femoral scutes are bent downward. The tail of the male is thicker at the base than that of the female, and has the vent beyond the carapacial margin.

Mauremys japonica is found on the Japanese islands of Honshu, Kyoshu, and Shikoku.

Fresh waters with slow currents and soft bottoms (ponds, marshes, swamps, canals, and streams) are preferred.

Natural History
Sexual maturity is reached in three to five years. The mating period starts in September and extends to April, but is interrupted in the mid-winter period; however, several other authors have reported the period June-August (Yasukawa et al., in press).
One to three clutches of 1-12 eggs are laid each year (Yasukawa et al., in press), with the number of eggs decreasing with each subsequent clutch. Normally 10 to 15 days pass between sequential nestings (Fukada, 1965). The white oval egg is brittle shelled and measures 36 x 22 mm. Fukada (1965) reported the incubation period to last about 70 days. Hatching may occur from late August to early October (Fukada and Ishihara, 1976).
Hatchlings have carapace lengths of 25-35 mm. Their medial keel is prominent and the carapace is very serrate posteriorly. Two low lateral keels are also present on the pleurals, and their carapacial color is brighter than that of adults. The hatchling plastron has either a large dark central blotch or a wide, dark seam-following pattern.
Mauremys japonica is omnivorous, taking weeds, fruits, earthworms, snails, insects, decapods, fishes and frogs (Yasukawa et al., in press).
Japanese pond turtles are fond of basking and sometimes wander about on land. In the cold season, they hibernate under rocks and piled up leaves in ponds and streams, but remain active at water temperatures as low as 5°C (Yabe, 1992).

IUCN Red List Status (1996)
Not listed.