South American snake-necked turtle
The oval, dark-brown carapace (to 30 cm) has nearly parallel sides and is relatively flattened. A medial keel is present in the form of posterior conical protuberances on vertebrals 1-4 and as an anterior conical protuberance on the 5th; these are well-developed in juveniles but become lower with age and may disappear entirely in very old turtles. Similar protuberances are found on the pleural scutes, and, although they also become lower with age, evidence of these can be found in even old individuals. The cervical scute lies behind the first two anterior marginals, but the nuchal bone beneath reaches the rim of the carapace by lying partially between the first two anterior peripheral bones. Vertebral scutes are all broader than long in juveniles, but in adults the 1st vertebral is as long as or slightly longer than broad, and the 4th vertebral may be as long as broad. Vertebral 1 is the largest and is anteriorly flared, the 4th is the smallest, and the 5th is posteriorly expanded. Since there are only six neurals, the 7th and 8th pairs of costal bones meet at the midline. There are 22 peripheral bones, and the lateral marginals are slightly upturned. The undersides of the marginals are brown and the narrow bridge is either brown or yellow with large brown blotches. The plastron varies from immaculate yellow to yellow with brown blotches. Its forelobe is longer than the hindlobe and more or less rounded anteriorly; the hindlobe has a deeper posterior notch than in H. maximiliani. The plastral formula is quite variable: intergul > an >< fem > gul >< abd > pect >< hum (for other shell comparisons with H. maximiliani, see Wood and Moody, 1976). The head is moderate in size with a short, slightly protruding snout and an upper jaw that is neither notched nor hooked. Its dorsal surface is covered with numerous irregularly shaped scales. No prominent valvelike flaps of skin occur at the corners of the mouth, as in H. maximiliani. The head is olive to gray with a broad, black-bordered white or cream-colored stripe extending from the upper jaw backward along the neck. Chin and undersides of the neck are yellow with dark spotting or vermiculations; the jaws are yellow or tan. The neck is longer than the vertebral column and its lateral surfaces contain numerous spiny tubercles. Limbs are olive or gray on the outer surfaces but cream to yellow beneath. The forelimbs have large transverse scales on the anterior surface; similar scales are found at the heel and up the posterior surface of the hindleg. There are four claws on each foot. The tail is olive gray.
Bull and Legler (1980) reported the diploid chromosomes total 58 (22 macrochromosomes, 36 microchromosomes).
Males have concave plastra with deep anal notches and longer, thicker tails with the vent beyond the carapace. Females grow larger.
Hydromedusa tectifera ranges from the states of Sao Paulo and Rio Grande do Sul in southeastern Brazil westward and southward through eastern Paraguay and the Chaco and Formosa of northeastern Argentina to Uruguay.
Hydromedusa tectifera is found in slow-moving, soft-bottomed ponds, marshes, lakes, streams, and rivers with some aquatic vegetation. In coastal regions, brackish waters may be entered. In the colder parts of its range, it may hibernate underwater, buried in the soft bottom.
Courtship and nesting behavior have not been described. According to Cei (1993), nesting occurs in spring when eggs are deposited in riverbanks. A captive female from San Antonio Zoo at intervals produced a total of 14 eggs; the largest clutch comprised 4 eggs (Benefield, 1979). The eggs are elongated (34 x 20 mm), white, and brittle shelled (Freiberg, 1981). Hatchlings are about 30 mm long and have more rugose carapaces than adults.
Hydromedusa tectifera is carnivorous, eating snails, aquatic insects, fish, and amphibians; it seems to prefer snails. In captivity it takes red meat, beef heart, shrimps, earthworms, larval mosquitos, and dry cat food (Kelderman, 1994). Cei (1993) thought this species may hibernate completely submerged.
IUCN Red List Status (1996)