William's mud turtle
The oval, black to dark-brown carapace (to 25 cm) is elongated, widest behind the center, moderately depressed medially, and contains a low, blunt vertebral keel. The 1st and 5th vertebrals are flared, and vertebrals 1-4 are as long as wide or longer than wide. Seven or eight (usually eight) neurals are present; neural 8 is elongated and only narrowly separated from the suprapygal (Broadley, 1983). Anteriorly the neurals are well-separated from the nuchal bone. The posterior marginals are not serrated. The large plastron covers most of the carapacial opening. Its anterior lobe is rounded and shorter than the posterior lobe. An anal notch is present, and the posterior lobe is slightly constricted at the level of the abdominal-femoral seam. The plastral formula is: abd > fem > hum > intergul > an > pect > gul. The intergular is broad (about 1.5 times broader than long). The bridge is wide but lacks an axillary scute. The plastron is either black with a yellow rim and midseam, or predominantly yellow. The head is broad with a slightly protruding snout, and the upper jaw may bear a pair of toothlike cusps. Two barbels occur on the chin. Head scalation is similar to that of P. castaneus. Head and limbs are brown; limb sockets yellow. Each foreleg has several enlarged transverse scales on its anterior surface.
Males have longer, thicker tails and slightly concave plastra.
Pelusios williamsi is endemic to the upper Nile drainage around Lakes Victoria, Albert, and Edward.
Three subspecies are recognized. Pelusios williamsi williamsi Laurent, 1965, the Lake Victoria mud turtle, occurs in the upper Nile drainage around Lake Victoria. The plastron is mostly black with a yellow midseam, the posterior lobe as long as or shorter than the anterior lobe, and the intergular scute more than half as long as the length of the anterior lobe. P. w. lutescens Laurent, 1965, the Albert Nile mud turtle, occurs in the Lake Edward-Semliki-Lake Albert drainage west of P. w. williamsi. Its plastron is yellow with some gray or brown spots, the posterior lobe as long as or longer than the anterior lobe, and the intergular scute less than half as long as the length of the anterior lobe. The Ukerewe Island mud turtle P. w. laurenti Bour, 1984a was described from Ukerewe Island, Lake Victoria. Its plastron is yellow with small dark spots along the sides of the gular scutes, the posterior lobe is longer than the anterior lobe, and the intergular is more than half as long as the anterior lobe. The 1st vertebral is very broad along the anterior seam but almost parallel sided posteriorly, thus presenting a T-shaped appearance.
Pelusios williamsi inhabits lakes, rivers, and swamps.
IUCN Red List Status (1996)