African dwarf mud turtle
Pelusios nanus is the smallest species of the genus. Its elongated oval carapace (to 12 cm) is flattened dorsally, and unserrated posteriorly (although a small notch may be present between the supracaudals). No cervical scute is present, and there is little, if any, evidence of a medial keel. Vertebral 1 is widely flared anteriorly and is broader than long in juveniles, but as long as or slightly longer than broad in adults. Vertebrals 2-4 are longer than broad in adults, but broader than long in juveniles; the 4th is the smallest vertebral. Vertebral 5 is flared posteriorly and is much broader than long. There are seven or eight neural bones; if only seven, it is the 8th which is lost. The 1st neural is anteriorly narrowed. Posterior marginals may be somewhat flared; lateral marginals are unkeeled. The carapace is brown, often with dark streaks. The plastron is large with a long anterior lobe (more than twice the length of the interabdominal seam), and a weakly developed hinge. Both the anterior and posterior plastral lobes are broad; the posterior lobe has an anal notch and is slightly constricted at the abdominal-femoral seam. The plastral formula is: fem > hum >< abd > an > intergul > pect > gul. Axillary and inguinal scutes are absent from the bridge; also the pectoral scute does not enter the bridge, which is formed entirely by the abdominal scute. The plastron is yellow with a black border; the bridge is black. The snout is short and blunt, and the upper jaw only slightly notched. There are two chin barbels. Forelimbs lack large transverse scales.
Males have concave plastra and long, thick tails; females have flat plastra and short tails.
Pelusios nanus occurs in southern Africa, from northern Zambia westward along the southern border of the Congo Basin to Angola (Broadley, 1981a).
Broadley (1981a) refers to it as an inhabitant of waterways in moist savannahs.
Haagner (1994) reported that a 11.9 cm Zambian female laid five fertile 28.3-30.2 mm x 14.9-16.9 mm eggs after 10 months in captivity with no male present, so this species is capable of sperm storage. She did not dig a nest cavity, but merely deposited the eggs on the surface of the cage. None of the eggs hatched; a 67 day-old embryo in one was perfectly formed with a carapace length of 15.7 mm.
Wermuth and Mertens (1961, 1977) designated P. nanus a subspecies of P. adansonii; however, additional evidence warrants that these be considered separate species. Laurent (1965) and Broadley (1981a) re-examined these species and found they differ in such features as size, coloration and pattern, shape of the carapace, development of the vertebral keel, width of the 3rd vertebral versus measurements of other scutes, and the absence of either the 1st (adansonii) or 8th (nanus) neural from the carapace. Also, the two species occupy mutually exclusive, widely separated geographic ranges. Although closely related, adansonii and nanus should both be considered valid species.
IUCN Red List Status (1996)