(Linnaeus, 1766)
Scorpion mud turtle
Recognition
The elongated, oval carapace (to 17.5 cm) is high domed, has three well-developed longitudinal keels (these may become lower with age until they are barely noticeable in large individuals), and is widest behind the middle. The 1st vertebral is flared anteriorly and is broader than long; vertebrals 2-5 are usually longer than broad. The 10th and 11th marginals are elevated above those preceding; the 10th is highest of all. Posterior marginals may be slightly flared. The carapace is light to dark brown or black; lighter individuals may have darkened seam borders. The plastron is well-developed with a single movable hinge between the pectoral and abdominal scutes, and no posterior anal notch, or only a slight one. It is not always large enough to completely cover the shell opening; the hindlobe is longer than the forelobe. The plastral formula is: abd > an > gul > hum > fem > pect. Axillary and inguinal scutes usually touch. Plastron and bridge are brown. The head is moderate to large in size with a slightly projecting snout and a hooked upper jaw. On the chin are two large anterior barbels followed by two or three smaller pairs. The head is grayish brown, darker dorsally, lighter laterally with small irregular dark spots; the jaws may be plain yellow or have some dark streaks. Neck, limbs, and tail are gray brown. Several enlarged transverse scales are on the anterior surface of the foreleg and on the heel of the hind foot. No vinculae are present.
The diploid chromosome compliment is 56; 24 macrochromosomes (12 metacentric or submetacentric, 12 telocentric or subtelocentric) and 32 microchromosomes (Barros et al., 1972; Killebrew, 1975b; Bickham and Baker, 1976b; Sites et al., 1979b).
Carapaces of both sexes are about the same length, but that of females is broader (Acuña Mesén and Márquez, 1993); the plastron of the male is slightly concave, that of the female flat. The male tail is long and thick with a terminal spine, that of the female short and spineless. Males have a greater amount of head pigmentation and greater development of the hooked upper jaw (Acuña Mesén and Márquez, 1993).
Distribution
Kinosternon scorpioides ranges at low elevations from southern Tamaulipas, Mexico, southward to northern Argentina, Bolivia, and northern Peru.
Geographic Variation
Kinosternon scorpioides is quite variable, and many different names have been applied to populations throughout its range. Currently, however, four subspecies are considered valid. Kinosternon scorpioides scorpioides (Linnaeus, 1766) ranges from southern Panama over most of northern So Ph America, being found in Ecuador, northern Peru, southern Bolivia, and northern Argentina eastward to the Guianas and Pará, Brazil. It is large (to 27 cm), has three well-developed carapacial keels, a narrow cervical scute, and a moderate-sized head. In this subspecies the anal notch is prominent (lacking or only shallow in the other subspecies), and the plastral hindlobe is narrow. The white-throated mud turtle K. s. albogulare (Duméril and Bocourt, 1870) ranges from Panama northward to Honduras. It is tricarinate, but somewhat flattened dorsally, usually lacks an anal notch on the plastron, and has a plain yellow lower jaw and chin in the female. K. s. cruentatum (Duméril and Bibron, in Duméril and Duméril, 1851) ranges from northeastern Nicaragua and Honduras northward to Veracruz and Tamaulipas, Mexico. This may be the most strikingly marked mud turtle. The sides of its head usually have bright red or orange spots, giving it the common name red-cheeked mud turtle. Also, the carapace may be yellow or slightly orange with dark seam borders, and the plastron orange. The three carapacial keels become lower with age, and its plastron can completely close. The last subspecies, K. s. abaxillare Baur, in Stejneger, 1925b, the central Chiapas mud turtle, occurs on the central plateau of Chiapas, Mexico, at elevations over 800 m. It is best identified by the absence of an axillary from the bridge causing the axillary-abdominal seam to be incomplete; all other K. scorpioides normally have an axillary scute. Also, it is a flatter turtle than its nearest relative, K. s. cruentatum.
Cabrera and Colantonio (1997) evaluated the taxonomic status of K. s. carajasensis Cunha, 1970 and K. s. seriei Freiberg, 1936 by reassessing their original descriptions and morphology. The presumed distinctive characters showed extensive overlap among both subspecies and K. s. scorpioides, and no new character was found that discriminated among the three subspecies. They suggested that the forms carajasensis and seriei be placed in the synonymy of K. s. scorpioides, and we agree. In addition, Berry (1978a) considered K. s. pachyurum Müller and Hellmich, 1936 a synonym of seriei, and thus now of K. s. scorpioides.
Habitat
This species lives in streams, rivers, lakes, and ponds. If its waterway dries up, it will bury itself in the mud bottom until the next rain.
Natural History
During courtship the male pursues the female with his head extended and normally bites her rump and legs. If she remains in position, he will often circle her, occasionally biting at her limbs or head. Finally he mounts from the rear, hooking his foreclaws under the rim of her shell for support, and intertwining her tail with his, inserts his penis. These observations on captives essentially agree with courtship behavior reported by Sexton (1960) and Fretey (1976).
Nesting occurs from March to May in Mexico (Alvarez del Toro, 1960) and Venezuela (Sexton, 1960).
Clutches vary from 6 to 16 eggs (Alvarez del Toro, 1960; Freiberg, 1981), but this latter number seems high and was perhaps based on a count of follicles rather than shelled eggs; the eggs are elongated (40 x 18 mm) with white, brittle shells. According to Cei (1993), a clutch of K. s. scorpioides (as seriei) consists of one to three 33-37 x 20-30 mm eggs. Alvarez del Toro (1960) reported the incubation period is about 3 months. Hatchlings have 30 mm carapaces.
According to Vanzolini et al. (1980) this turtle is omnivorous, eating fish, snails, adult amphibians, insects, algae, and other plants. In captivity, it readily adapts to a fish diet.
IUCN Red List Status (1996)
Not listed.