Hydromedusa maximiliani

(Mikan, 1820)
Maximilian's snake-necked turtle

The oval, dark-brown carapace (to 21 cm) has nearly parallel sides and is dorsoventrally flattened. A low medial keel is present in the form of posterior protuberances on vertebrals 1-4 and as an anterior protuberance on the 5th; the keel may disappear with age. The cervical scute lies behind the first two anterior marginals. Similarly, the nuchal bone lies behind the anterior peripheral bones and does not reach the carapacial border. Vertebrals are broader than long throughout life; the 1st is the largest and is anteriorly flared, the 4th is the shortest, and the 5th is posteriorly expanded. Seven to nine neurals lie beneath the vertebral scutes, and the 8th pair of costal bones may touch at the midline. Peripheral bones total 22-24, and the lateral marginals are slightly upturned. The posterior carapacial rim is smooth in adults. Plastron, narrow bridge, and undersides of the marginals are cream to yellow with some dark seams or brown areas. The plastral forelobe is longer than the hindlobe and is rounded in front; the hindlobe has a shallow posterior notch. The plastral formula is quite variable: intergul > an >< fem > pect >< hum >< gul > abd. The head is moderate in size with a short, slightly protruding snout and an upper jaw lacking a medial notch or hook. Its dorsal surface is covered with smooth skin, but the skin behind the eyes is divided into scales. A prominent valvelike flap of skin is present at each corner of the mouth. The head is brown to olive gray dorsally and cream colored laterally and ventrally; there is a sharp break between these colors just below the level of the tympanum. The tympanum in some contains a dark central spot surrounded by white pigment. The jaws are cream to yellow. The neck is longer than the vertebral column, colored like the head, and has numerous spiny tubercles on its sides. Limbs are olive gray on the outside, but cream to yellow beneath. Forelimbs have large transverse scales on the anterior surface, while similar scales are found at the heel and up the posterior surface of the hindleg. The toes are webbed and there are four claws on each foot. The tail is olive dorsally and ventrally, but yellow laterally. Souza (1995) reported that the carapace of hatchlings and juveniles to 12.2 cm was uniformly brown or dark gray, with the lower border of the marginals yellowish, with black seams in some individuals. The plastron was either completely dark with a yellowish bridge or yellowish with peripheral dark spots. The iris was black. Top and sides of the head and neck and dorsal side of the limbs were brown or olive-gray; ventral side of the limbs was yellowish or cream. The carapace rim was serrate from marginal 7 rearward, but the serrations disappear with growth.
Males have concave plastra with deeper anal notches, and longer, thicker tails with the vent beyond the carapacial rim.

Hydromedusa maximiliani is restricted to the states of Espírito Santo, Minas Gerais, Rio de Janeiro, and São Paulo in southeastern Brazil.

Souza and Abe (1995) reported that this turtle lives in clear, shallow, rocky streams in hill and montane terrain, but it has also been collected from shallow, soft-bottomed pools.

Natural History
A female captured in November 1988 in the Carlos Botelho State Reserve laid three 40 x 25 mm eggs in January 1989 (Yamashita, 1990). The hatchling carapace is about 47.3 mm (Souza, 1995).
H. maximiliani is carnivorous, consuming at least 12 orders of insects, oligochaetes, leeches, decapods (most notably Aeglia odebrechi; Yamashita, 1990), amphipods, amphibians, mammals (possibly as carrion), perhaps fish, and occasionally some plant material (Souza and Abe, 1995).
Yamashita (1990) observed one individual basking on a stone, and reported that turtles usually rest at curves in streams where leaves accumulate. The dimmed light and the general resemblance of their carapace to that of a dead leaf make these turtles very cryptic in this microhabitat.

IUCN Red List Status (1996)
Vulnerable (B1+2cd).