Acanthochelys radiolata

(Mikan, 1820)
Brazilian radiolated swamp turtle

Acanthochelys radiolata is a medium-sized (to 20 cm) South American side-neck with radiating striations on the carapace. Its flattened elliptical carapace has a very shallow dorsal groove between the 2nd and 4th vertebrals. In adults, the 1st and 5th vertebrals are much broader than long; the 1st is broadest of all, the 2nd and 3rd are usually only slightly broader than long, and the 4th may be longer than broad. Anterior- and posteriormost marginals are broadest; those lateral are narrowest and slightly upturned. Posterior marginals are slightly flared and serrated; there is a slight posterior notch. Both vertebrals and pleurals contain numerous striations radiating anteriorly from the posterior margin of each scute. The carapace is highest at the level of the seam separating vertebrals 1 and 2, and broadest at the level of marginals 6-8. The carapace is uniformly dark olive, gray, or black. Plastron and bridge are yellow with either a large dark blotch or dark mottlings on each scute, or with dark seam borders. The slightly upturned forelobe is broader than the hindlobe, which contains a posterior notch. The length of the intergular scute is slightly less than half (48-49%) that of the plastral forelobe. The plastral formula is: intergul > fem >< abd > hum > gul > an > pect. The head is olive to grayish brown dorsally and yellow laterally and ventrally. The unnotched jaws are yellow to tan and may contain some dark mottling. Dorsally, the head is covered with numerous irregularly shaped scales. The snout is short and only slightly projecting. Two small yellow barbels are present on the chin, and the iris is white. The neck is olive to brown dorsally and yellow ventrally. Its dorsal surface contains numerous very short, rounded tubercles. Tubercles on the sides are fewer and smaller. Anterior surfaces of the limbs are covered with large scales. The thighs have a few scattered, small, pointed tubercles. Outer limb surfaces are olive or brown and the inner surfaces yellow. The olive to brown tail is short.
Males have concave plastra and longer, thicker tails with the vent beyond the carapacial margin; females have flat plastra and short tails with the vent under the carapace.

Acanthochelys radiolata occurs entirely within Brazil, ranging from the states of Bahia, Minas Gerais, and Mato Grosso southward to the vicinity of the city of São Paulo.

Geographic Variation
None has been reported. However, some authors (Pritchard, 1979) consider Acanthochelys spixii a subspecies of A. radiolata. There are fundamental differences between these forms (see recognition sections of each), and it is best to consider them separate species.

Acanthochelys radiolata lives in slow-moving waters with soft bottoms and abundant aquatic vegetation.

Natural History
Ewert (1979) reported that two hatchlings had a mean carapace length of 41.9 mm, but we have seen a 30.5 mm hatchling. Hatchlings have grayish brown carapaces with a wedge-shaped yellow mark on each marginal. The plastron is yellow with a large, dark central blotch which extends outward along the seams. The yellow bridge contains two dark spots. The underside of the throat and neck is yellow to cream with large dark blotches. Due to their relatively large heads, Acanthochelys radiolata hatchlings may be confused with Phrynops hatchlings, but on each hindleg there is a pretibial flap of large scales that is never found in Phrynops.
This is a rather shy turtle in captivity, often hiding much of the time. It seems to be exclusively carnivorous, accepting a variety of animal foods such as fish, amphibians, aquatic insects, snails, and worms. Sometimes it climbs onto the land to bask or roam about.

IUCN Red List Status (1996)
Lower risk: near threatened.