Genus Phrynops

Wagler, 1830
Toad-headed turtles

The genus Phrynops contains 12 variable South American freshwater species, the taxonomy of which is still debated. The carapace varies from flat topped, with or without a medial keel, to peaked with a prominent medial keel. A pair of lateral keels may also occur along the pleural scutes. Neural bones vary from none (in some P. gibbus and female P. zuliae) to three to six, and the nuchal bone extends to the anterior carapacial rim. Where there are no neural bones to separate them, costal bones meet at the midline. The cervical scute is rather small, and when present reaches the carapacial rim. The plastron is large, lacks a hinge, and has the intergular separating the gulars but not entirely separating the humerals. Axillary buttresses are very strong; inguinal buttresses are also strong and ankylosed to the 5th costal bones. The skull is broad and somewhat flattened. Its prefrontal bones do not meet at the midline, and the temporal arch is moderate and formed by the squamosal and parietal bones. The narrow dorsal portion of the parietal covers little of the adductor fossa, and while always present, may be greatly reduced; the parietal does not touch the supraoccipital. The dorsal horizontal portion of the supraoccipital is not expanded. On the roof of the mouth there is vomer-palatine contact, as the palatines are not reduced. There is no contact between the quadrate and basisphenoid. No triturating ridges are present. Chin barbels are present. The toes are fully webbed and each forefoot has five claws.

Phrynops has been divided into three subgenera (Zangerl and Medem, 1958):
(1) Mesoclemmys Gray, 1873c includes Phrynops gibbus and Phrynops
vanderhaegei, small species with only rudimentary or no neural bones and having moderately sized heads, small chin barbels, and relatively short intergular scutes (shorter than or about the same length as the combined lengths of the interhumeral and interpectoral seams).
(2) Batrachemys Stejneger, 1909 includes the species Phrynops nasutus, Phrynops dahli, Phrynops raniceps, Phrynops tuberculatus, and Phrynops zuliae. These are larger species usually with three or four neural bones in males, and a very large broad head, long chin barbels, and an intergular scute longer than, or almost as long as, the combined lengths of the interhumeral and interpectoral seams.
(3) Phrynops Wagler, 1830 includes the remaining five species, Phrynops
geoffroanus, Phrynops hilarii, Phrynops hogei, Phrynops rufipes and Phrynops williamsi, which generally fall between the other two subgenera in carapace length and head size, have up to six neural bones, very long chin barbels, and an intergular scute as long or almost as long as the combined lengths of the interhumeral and interpectoral seams. Serious doubts as to the validity of this subgeneric arrangement have been raised by Bour (1973) and Gaffney (1977), and further study into the relationships within this genus is needed.

Species identification
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