The South American twist-necked turtles, Platemys platycephala, are the last remaining turtles in the genus Platemys. The other previous members have been recently reclassified (1985) into the genus Acanthochelys. Like many other South American turtles, Platemys are pleurodires or side-necked turtles. The species name, platycephala, is derived from the Greek roots platys (flat) and kephale (head) and thus literally means flat-headed or flat-shelled turtle. According to Pritchard, the common name twist-necked turtle is apparently from the Guyanan word cashipan.
There are two recognized subspecies, Platemys platycephala platycephala and P. platycephala melanonota. The sub-specific name melanonota is from the Greek root melas meaning black. My experience and this article deal exclusively with Platemys platycephala platycephala.
Their range includes most of the northern half of South America, including: the Orinoco to all but the upper Amazon basin in Venezuela, Columbia, eastern Ecuador, Peru, northern Bolivia, the Guianas and northern Brazil.
As suggested by its scientific name, the twist-necked turtle has a very flat head and carapace. The carapace is oval in shape and has a broad median groove created by two keels running virtually the entire length of the carapace. This double keel is very distinctive. The carapace coloration of my three specimens is an unusual patchwork of light to dark browns with streaks of black. The plastron is uniformly dark brown or black with a yellowish rim that extends to the marginal scutes. The flat head is a dull orange in color, and the neck is covered with tubercles that diminish in size toward the base of the neck. The skin on top of the head is smooth and undivided, without large scales. The remainder of the skin is very dark or black and the legs are covered with large black scales. The legs and feet have the appearance one usually associates with a turtle that spends a good deal of time on land.
Adults reach a maximum length of about 6 inches, with tail size being the best indicator of gender (longer and thicker for males, of course). Mating takes place year-round with the females laying 4-6 eggs, sometimes quite a distance from water.
Pritchard writes that the twist-necked turtle is basically aquatic but is quite often found wandering on land after rain. (If mine waited for rain before they went walking around we'd never see them...). My Platemys p. platycephala spend as much time on land as they do in the water, maybe more.