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Pelomedusidae are primitive, semiaquatic turtles that belong to the Pleurodira or side-necked turtles. They are naturally found in Africa, Madagascar and some of the Seychelles Islands. Present day Pelomedusidae are compromised of two genera: Pelomedusa and Pelusios. Pelomedusa is separable from Pelusios by the unhinged, rigged plastron and mesoplastra that are widely separated. The bridge of Pelomedusa is formed by the pectoral and abdominal scutes, both contributing a nearly equal part. The bridge of Pelusios is formed only by the abdominal scutes. All Pelusios species have a hinge between the pectoral and abdominal scutes and the mesoplastral bones touch at the midplastral seam. The hinge allows Pelusios species to lift the anterior lobe. With the head and feet retracted, the lifted anterior lobe closes up and leaves the front of the turtle nearly invulnerable to predatory attacks.
All Pelomedusidae have 5 claws on their hind feet. There never is a cervical scute and the gular scutes on the plastron are always separated by an intergular scute.
All Pelomedusidae are highly dependent on water and all are encountered in watery habitats. Though some of those habitats may dry up during the dry season and many Pelomedusidae estivate buried in the dry mud until the water returns.
Quick identification between Pelomedusa and Pelusios.
Anatomy of the Pelomedusidae.
Pelomedusa and Pelusios have a quite similar appearance concerning their epidermal scute arrangements. One thing that quickly meets the eye is the broad first vertebral scute of Pelomedusa. The intergular scute is small with Pelomedusa and variable in form in Pelusios species. In general Pelomedusa are flat turtles where most Pelusios are quite domed, especially in females.
Recognition of species in the genus Pelusios.
Traditionally the Pelusios species have been divided into 2 groups: the Pelusios adansonii group and the Pelusios subniger group. These groups are divided by the difference in the length of the anterior lobe in comparison to the abdominal scutes. With the Pelusios adansonii group the anterior lobe is 2-2,5 times the length of the interabdominal seam while the members of the Pelusios subniger group have an anterior lobe that is 1-1,5 times the length of the abdominal scutes.
The Pelusios adansonii group contains the species Pelusios adansonii, P. broadleyi, P. gabonensis, P. marani and P. nanus. The Pelusios subniger group contains the remaining species which are: P. bechuanicus, P. carinatus, P. castaneus, P. castanoides. P. chapini, P. cupulatta, P. niger, P. rhodesianus, P. seychellensis, P. sinuatus, P. subniger, P. upembae and P. williamsi.
For identification purposes only we will rearrange the group divisions, adding a third group. This new group will be called the Pelusios castaneus group. This group contains all species from the Pelusios subniger group minus Pelusios bechuanicus, P. subniger and P. upembae. These three species will be maintained within the Pelusios subniger group. The Pelusios castaneus group resembles the Pelusios subniger group in the classic way.
The Pelusios subniger group is differentiated from the Pelusios castaneus group because the species in this group have a strong constriction at the abdominal-femoral seam, making the plastron have the appearance of an 8-shape. The species in the Pelusios subniger group also have broad heads, the heads being as broad as half the abdominal-femoral seam.
Recognition on species level.
For recognizing Pelusios turtles on species level we developed a diagram. This diagram shows 9 points of articulation (A-J) on the carapace and plastron that are different among the species. We prefer this manner of working because this way deformed turtles still can be determined. Deformation often occurs with captive turtles. Using a single character key to the species will leave room for misinterpretations.
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