Siebenrockiella crassicollis

(Gray, 1831b)
Black marsh turtle

This almost totally dark-brown or black turtle has an oval, depressed, tricarinate carapace (to 20 cm) with a strongly serrated posterior margin. It is widest behind the middle. The medial keel is always distinct, but the two lateral keels on the pleural scutes are less pronounced in larger individuals. Vertebrals of adults are dorsally flattened and the first four are usually wider anteriorly and rather narrow posteriorly, but the 5th is broader posteriorly than anteriorly. The underlying neural bones are not elongated and are shortest anteriorly; those in the middle of the series are almost square. The plastron is well-developed, hingeless, and extensively sutured to the carapace. It has a posterior anal notch, and its lateral borders may be slightly keeled, at least as far posteriorly as the femorals. The humero-pectoral seam crosses the underlying entoplastron. The plastral formula is: abd > pect > fem > an > gul > hum. Width of the bridge is about equal to the length of the plastral hindlobe, and it is well-buttressed; the axillary buttress attaches midway along the 1st costal and the inguinal buttress about a third of the way along the suture between the 5th and 6th costals. Axillary and inguinal scutes are moderate to large. Bridge and plastron vary from uniformly black or dark brown to yellowish brown with dark blotches or an extensive dark seam-following pattern. The head is large and rather broad with a short, slightly projecting snout. In the skull, the quadratojugal touches both the jugal and postorbital, and the posterior palatine foramen is slightly larger than the small orbito-nasal foramen. The upper jaw is medially notched, with a narrow, ridgeless triturating surface. The head is black to dark gray with a faded white, cream, or yellow spot behind each orbit, and cream to tan jaws. Posteriorly, the head is covered with small scales, and another narrow strip of small granular scales lies between the orbit and tympanum. The black or dark-gray neck is thickened, making the head appear shorter. Limbs and tail are dark gray to black. Toes are webbed, and the anterior surface of the forelegs is covered with large transverse scales.
Killebrew (1977a) reported the diploid karyotype to be 52, but previously Stock (1972) and Bickham and Baker (1976a) had found it to be 50. Bickham and Baker (1976a) also reported the single individual they examined was heterozygous for a presumed pericentric inversion. Further study by Carr and Bickham (1981) has confirmed heteromorphism in a pair of macrochromosomes in the male, which they interpreted as an XX/XY sex-determining system, the first discovered in the Emydidae and the only such system in turtles other than that found in the kinosternid genus Staurotypus.
Males have slightly concave plastra and thicker, longer tails than do the flat-plastroned females. Females often retain the light head spots, while these spots fade out in males.

This common turtle ranges from southern Vietnam westward through Thailand to Tenasserim in Myanmar, and southward through Malaysia to Sumatra, Java, and Borneo.

Siebenrockiella lives in water bodies with slow current, soft bottoms, and, often, abundant vegetation; shallow streams, rivers, ponds, lakes, marshes, and swamps may all afford suitable habitats.

Natural History
A captive male we observed courting frequently bobbed his head at the female as he pursued her around the tank. Honegger (1986) observed males biting females first in their forelegs, then in their sides and hindlegs and later also in their 7th to 10th marginals.
According to Dr. Edward Moll, Siebenrockiella crassicollis in Malaysia may lay three or four clutches of one or two eggs each during a nesting season extending from April through June. In captivity, a clutch consists of a single hard-shelled, elongated (X = 52.1 x 28.0 mm), white egg that is laid throughout the year (but with a peak from April to July; Honegger, 1986). Incubation at 29-30°C takes 68-84 days, but may take up to 112 days at 25°C; hatchlings are 43-46 mm and weigh 14-15 g (Honegger, 1986).
Predominantly carnivorous, Siebenrockiella feeds on worms, snails, slugs, shrimp, and amphibians; it also scavenges dead and decaying animals, and Nutphand (1979) reported it will eat rotten plants which have fallen into the water. Captives from Zoo Zürich were reported to be omnivorous, feeding on beef, fish, shrimps, earthworms, snails, and fruits such as grapes, bananas and figs (Honegger, 1986). Most food is captured or consumed underwater, but Nutphand (1979) stated that it comes onto land at night to forage for food or to mate.
S. crassicollis is a bottom dweller, spending much of the time partially buried in mud; however, at least in captivity, it occasionally basks.

IUCN Red List Status (1996)
Not listed.