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Carapace
• Up to 285 mm in length (females).
• Oval of form and broadest behind the center.
• The carapacial posterior rim is not serrated.
• The 1st vertebral is wider than long and flared anteriorly.
• The 5th vertebral is wider than long and flared posteriorly.
• Vertebrals 2 through 4 are as broad as long or slightly longer than broad.
• The intermarginal seam of the first marginals fits 3 to 5 times in the length of the first vertebral.
• The vertebrals may be flattened or even depressed.
• No keel but often a small protuberance on the 4th vertebral is retained.
• The color varies from black, brown, chestnut, olive to caramel.
Plastron
• The plastron is large and almost covers the carapacial opening.
• Short anterior lobe, about 1 to 1,5 times the length of the interabdominal seam.
• The hinge of the anterior lobe is located at the midline of the 5th marginal scute.
• The intergular is about 1,3 to 1,5 times as long as broad.
• The anterior rim of the intergular is smaller than the anterior rim of the gulars.
• The bridge is long.
• The bridge has the same color as the carapace.
• The abdominal scutes are long and the abdominal-femoral seam is straight.
• Slight or no constriction at abdominal-femoral seam.
• The anal notch is deep and sharp.
• The plastron is yellowish with the plastral outer edges colored in the color of the carapace.
Limbs, tail and neck
• The hind feet are heavily webbed.
• The forelegs have many transverse scales on the anterior surface.
• The skin in the neck has very fine scales.
• Legs, tail and neck are light gray to yellowish colored, becoming dark gray or brownish towards the outer surface.
Head
• The head is moderate in size.
• The snout is slightly protuding and might be blunt or pointed.
• The upper jaw has 2 tooth-like cusps.
• The chin has 2 barbels.
• The seam between frontal and temporal scales is moderate.
• Supralabial scale usually abscent, though when present, it is small.
• The parietal triangles are moderate in size.
• The head is grayish to brownish and with very dark vermiculated markings.
• The upper jaw has dark vertical streaks.
Clearly visible with Pelusios castaneus are the two cusps on the upper jaw.
Differentiating Pelusios castaneus from Pelusios subniger.
Pelusios castaneus and Pelusios subniger are very often confused with one another. This is often caused by literature in which both species are confused. These misidentifications even occur in reasonable modern literature. Actually it is rather strange that so much confusion exists as these two species are quite easily to set apart from each other. Let us indicate the differences that are easily visible in both species.
A: the width of the first pair of marginal scutes is large in Pelusios castaneus with the width being about 95% of the anterior margin of the first vertebral scute. Mostly the first marginals almost line up with the first vertebral. The first marginals are oblong of form. Pelusios subniger has short first marginals, almost quadrangular of form and they have contact with the first vertebral over about 55-85% of the anterior margin.
B: the width of the vertebral scutes, especially the 2nd, 3th and 4th vertebral. These vertebrals are in Pelusios castaneus longer than broad. The vertebrals are broader than long or equally broad as long in Pelusios subniger.
C: the shape of the carapace in Pelusios castaneus is elongated while the shell of Pelusios subniger is more or less circular in shape.
D: the anterior margin of the intergular scute is less width than the anterior margin of the gular scutes in Pelusios castaneus. The anterior margin of the intergular scute is quite broader than the anterior margin of the gular scutes in Pelusios subniger.
E: The plastral shape of Pelusios castaneus is a “normal” shape, a shape that is following more or less the form of the shell’s marginal border. Pelusios subniger has a rather unique plastral form with a strong constriction where the abdominal and femoral scutes meet. This constriction causes the plastral form of Pelusios subniger to have the shape of a guitar or an 8. Because of the constriction the relative head width of Pelusios subniger is about the half of the length of the seam between the abdominal and femoral scutes while the relative head width in Pelusios castaneus is far less than half of the length of the seam between these two pairs of scutes.
F: the seam between the abdominal and femoral scutes is straight with Pelusios castaneus. The seam between the abdominal and femorals scutes is slightly curved outwards with Pelusios subniger.
G: the coloration of the limbs of Pelusios castaneus is a yellowish to light gray with the outsides being darker, being dark gray to brownish. The coloration of the limbs of Pelusios subniger is most often a monotone gray with darker gray to blackish outsides.
H: the head of Pelusios castaneus almost always shows the typical vermiculated pattern of dark colored small lines covering the gray to brownish head. Pelusios subniger has no colorful pattern on the head, which is a monotone color in the same coloration of the limbs, sometimes a brownish color. Hatchlings and young juveniles of Pelusios subniger might show a vermiculated pattern of a darker color on top of the head, or even some dark speckles.
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