Cope, 1865
Narrow-bridged musk turtle
Recognition
The oval carapace (to 16.5 cm) usually bears three longitudinal keels which become obscured with age. Posterior marginals are unserrated and unflared; the 10th, and sometimes also the 11th, is elevated above the preceding marginals. Vertebrals 1-4 are broader than long, but the 5th is longer than broad or about equal in these dimensions. The 1st vertebral is widely flared anteriorly and touches the first two pairs of marginals. There are six to eight neurals. The posterior pair of costals meet at the dorsal midline, but are separated from the posteriormost peripheral by a large suprapygal. Carapacial scutes may be roughened due to growth annuli and radiations. The carapace is dark brown or yellowish brown with dark seams. Juveniles and young adults may also have a pattern of dark radiations. The hingeless plastron is very small and cruciform. The bridge is extremely narrow (only about 5% of the plastron length; Smith and Smith, 1979), and the rest of the plastron is connected to the carapace by a ligament. Axillary and inguinal scutes may be absent. Gular and humeral scutes are absent; the plastral formula is: pect > fem > an > abd. Both the anterior and posterior lobes are triangular in shape. In the bony plastron, the hyoplastra are fused with the hypoplastra, and an entoplastron is present. Iverson and Berry (1980) pointed out that growth of the abdominal scute is directed anteriorly instead of posteriorly as in Kinosternon. Both plastron and bridge are yellow; the juvenile plastron has a dark median blotch extending outward along the seams. The head is large with a slightly projecting snout and a sharply hooked upper jaw. In addition, a pair of cusps are present on the upper jaw just below the anterior margin of the orbit. The lower jaw also has a very long medial hook. The round to oval rostral shield is relatively small but does extend posteriorly to the orbit. Only one pair of barbels is present on the chin. In the skull, the squamosal does not touch the jugal, the frontal bone does not contribute to the orbital rim, and the pterygoid barely touches the maxilla. Small processes from the prootic and pterygoid bones divide the foramen of the trigeminal nerve into two distinct holes. Only a slender bar of bone separates the orbit from the emarginated temporal fossa. The head is yellowish brown to gray with dark mottlings, and the yellowish jaws contain dark streaks. The neck has several rows of tubercles and is gray with dark mottlings. The limbs are gray brown with webbed toes. Three large transverse scales occur on the anterior surface of the forelegs.
Moon (1974) reported the diploid chromosome number as 54, but Kiester and Childress (in Gorman, 1973) found 56 chromosomes.
Males are larger (to 16.5 cm) than females (to 15 cm) and have long, thick tails tipped with a horny spine and patches of roughened scales (vinculae) on their thighs and crura.
Distribution
The narrow-bridged musk turtle ranges, at low elevations, from central Veracruz and northern Oaxaca southward through northern Guatemala to Belize, but excluding the Yucatán Peninsula.
Habitat
Claudius angustatus lives in areas with seasonally flooded grasslands, and shallow water bodies with soft bottoms, such as marshes, ponds, and small streams. Pritchard (1979) thought that its rather thin shell and exposed soft parts caused Claudius to select shallow waters to avoid predation from crocodiles. At times it wanders on land, and has been found aestivating during the dry season in underground burrows (Duellman, 1963; Pritchard, 1979).
Natural History
Nesting occurs at the onset of the dry season in November and lasts till February (Flores-Villela and Zug, 1995); several clutches may be deposited. A typical clutch is 2-3 (1-6), hard-shelled, ellipsoidal (26.4-33.8 x 16.2-19.7 mm) eggs (Flores-Villela and Zug, 1995). Females do not dig a nest pit in the soil, but lay their eggs on or within the vegetation. Incubation is rather long, 95-229 days at different temperatures under laboratory conditions (Flores-Villela and Zug, 1995). Hatchlings are about 35 mm in carapace length (Ewert, 1979) with three well-developed keels. Their carapaces are dark brown or black, and their plastra are yellow.
Claudius, like other kinosternids, is carnivorous, eating worms, snails, aquatic insects, amphibians, and fish.
These turtles have a nasty temperament and bite viciously when first caught. After being in captivity for some time, they often mellow and allow themselves to be handled without snapping.
IUCN Red List Status (1996)
Lower risk: near threatened.