Description: A large sized turtle with adult females growing to 13.5 inches (34.3 cm) and adult males achieving 11 inches ( 28 cm) in straight carapace length.
The relatively low profile green to olive brown carapace has a medial keel that becomes less noticeable as the turtle ages. However as the turtle matures longitudinal ridges form in the carapace causing a textured appearance. Among adult specimens, the carapace is ovalesque to pear like and widest at the midsection. More variation tends to occur in the shells of the males. The posterior marginal scutes are often serrated and among some males these may be slightly flared upwards. Among populations within the San Saba River there are documented variations in the shape of the carapace among males from a dorsal appearance from round to pear-like. The creamy yellow plastron is almost as long and wide as the carapace the bridge is wide and a notch is present on the posterior portion. The carapace is olive to brown with yellow lines creating a reticulating pattern. Dark spots surrounded by whorls are also present on the dorsal and ventral surface of the marginal scutes and are divided by the suture line separating each marginal scute.
The head is dark green with thin yellow lines extending from the tip of the nose along the top of the head and the interior of the nostrils is yellow to yellowish green. The coloration of the lines can vary depending upon the age of the specimen from bright to creamy yellow. Two large stripes are present on top of the head and a thin yellow border is present just behind the eye. Two yellowish stripes extend from the eye, one running downward diagonally from underneath the eye across the corner of the mouth downward alongside the neck. The other other stripe reaches from behind the eye and extends along the neck. In some specimens these stripes may be broken. A creamy white to yellow lines extends down the mid-line of the throat forming an upside down "Y"is also present.
The limbs are also dark green to black with reddish-orange lines and marking on the feet and rear legs. A row of serrated scales is also present along the outer edge of the forelimbs. A suffusion of pinkish-orange is often visible on the outer edges of the limbs and amid the webbing between the toes.
Reticulate melanism is an age related condition seen among mature males in which the base coloration of the carapace turns orange to reddish orange with a dark net-like or reticulating pattern. The coloration of the face and limbs also changes to a lighter tone. This condition although seen in nature among this species has yet to be officially described (see last image in series from McLennan County).
Texas cooters are abundant and common throughout their range in the Brazos, Colorado River and San Antonio systems. Logs, rocks, shorelines, fallen trees and floating mats of vegetation all provide locations where it may be seen gregariously basking with several other turtle species.