Kinosternon leucostomum

(Duméril and Bibron, in Duméril and Duméril, 1851)
White-lipped mud turtle

The dark-brown or black, oval carapace (to 17.4 cm) is flattened to concave across the vertebrals and drops off abruptly to the rear. Juveniles and young adults have a single vertebral keel, which becomes lower with age until it may totally disappear. The 1st, 3rd, and 4th vertebrals are broader than long, the 1st broadest of all; the 2nd and 5th may be longer than broad in adults. The 1st vertebral touches the first two marginals, and the 4th pleural scute usually touches the 11th marginal. The cervical scute is very narrow. Lateral marginals are downturned, but those posterior are somewhat flared. Marginals 10 and 11 are higher than the previous nine; usually these two are the same height, but occasionally the 10th may be slightly higher than the 11th. Carapacial seams become deeply grooved with age. A single hinge lies between the pectoral and abdominal scutes which allows the large plastron to completely close the shell; it is not notched posteriorly, or only slightly so. The plastral formula is: an > abd > hum > gul > fem > pect; the gular scute is usually less than 55% of the length of the plastral forelobe, and the interabdominal seam length is less than 27% of the plastral length. The axillary scute is short, the inguinal much longer; these usually touch on the bridge. Plastron and bridge are yellow with darker seams. The head is moderate in size with a protruding snout and a hooked upper jaw. It is brown with cream-colored jaws (some dark streaking may occur on the jaws). A broad yellowish stripe extends backward from each orbit to the neck. This stripe may be bronze to light brown with small gold flecks in some individuals. Two large barbels followed by a pair of smaller barbels occur on the chin. The limbs are grayish brown with lighter gray sockets, and each foreleg has several large transverse scales just above the wrist and a rough fringe of small scales along its outer border. On the heel of the hind foot is a series of horizontal scales; vinculae occur on the thighs and crura of males. A horny spine adorns the tip of the tail.
The karyotype is 2n = 56; 26 macrochromosomes, 30 microchromosomes (Kiester and Childress, in Gorman, 1973; Killebrew, 1975b).
Males grow larger (17.4 cm) than females (15.8 cm) and have long, thick tails and broader heads. The female tail is very short.

Kinosternon leucostomum ranges from central Veracruz, Mexico, southward in the Atlantic drainages to Nicaragua, and then southward in both Atlantic and Pacific drainages to Colombia, Ecuador, and northwestern Peru.

Geographic Variation
Two subspecies are currently recognized by Berry (1978a). Kinosternon leucostomum leucostomum (Duméril and Bibron, in Duméril and Duméril, 1851), the northern white-lipped mud turtle, occurs in the Atlantic drainages of southern Mexico at elevations of less than 300 m, from central Veracruz southward across the base of the Yucatán Peninsula to Belize, Guatemala, and northern Nicaragua. Its carapace is high and the plastron is large; the mean width of the plastron at the anterior hinge is 73% of the maximum carapace width in both sexes, and 69% in males and 70% in females at the midfemoral width. Gular scute length is about 14-15% of the carapace length. The inguinal scute is long and usually touches the axillary. Vinculae are poorly developed, and the light postorbital stripes are obscure or disappear in adults. The southern white-lipped mud turtle K. l. postinguinale (Cope, 1887) occurs in the Atlantic and Pacific drainages from the Rio San Juan in Nicaragua southward to Colombia, Ecuador, and northern Peru. This subspecies has a relatively flattened carapace and a narrower plastron; the mean width of the plastron at the anterior hinge is only 69% of the maximum carapace length in males and 71% in females, and at the midfemoral width, only 66% in males and 68% in females. The gular scute is short, only about 12% of the carapace length. The inguinal is set well back on the bridge and is separated from the axillary. Vinculae are well-developed in males, and the postorbital stripes are usually well-marked.

This species occurs in most quiet waters with soft bottoms and abundant vegetation: marshes, swamps, streams, lagoons in rivers, and ponds. Morales-Verdeja and Vogt, 1997) reported linear home ranges of 50-200 m parallel to the shoreline of a temporary lake. Over the greater part of the range these waterways are within low-altitude forests.

Natural History
Nesting occurs at night, possibly throughout the year (Medem, 1962; Moll and Legler, 1971); but two nesting peaks occur in southern Veracruz, Mexico, one at the beginning of the heavy rains in late August to early September, and the other at the beginning of the dry season in mid-February to mid-March (Vogt and Flores Villela, 1992; Morales-Verdeja and Vogt, 1997). The two peaks may represent the beginning and end of the reproductive season there. The embryos probably undergo diapause, as in other Kinosternon species. Eggs are either deposited in shallow excavated nest cavities or are laid on the surface of leaf litter or on the ground and then covered with leaf litter and debris (Morales-Verdeja and Vogt, 1997).
A typical clutch includes one to three eggs, with single-egg clutches most common. Shells are brittle and eggs are elongated (37 x 20 mm). Eggs naturally incubated by Moll and Legler (1971) hatched in 126-148 days. A typical hatchling has a carapace length of about 33 mm.
Kinosternon leucostomum is nocturnal and apparently an omnivorous generalist. Plant material (fruits, seeds, shoots, leaves), aquatic insects, arachnids, crustaceans, snails, worms, fish, amphibians (mostly tadpoles), reptiles, mammals, and some carrion are eaten (Medem, 1962; Moll and Legler, 1971; Vogt and Guzman, 1988). It probably only feeds in the water, and populations feeding predominately on animal foods grow faster and larger and produce larger clutches of larger eggs (Vogt and Guzman, 1988).
K. leucostomum is not confined to water and often wanders extensively on land. Some individuals may aestivate in tropical rainforests as far from water as 600 m (Morales-Verdeja and Vogt, 1997). Medem (1962) reported it enters brackish water.

IUCN Red List Status (1996)
Not listed.