Black Marsh Turtle

Fascinating facts about the Black Marsh Turtle

• A single adult black marsh turtle usually measures just 17 cm (6.7 in) long, yet some individuals can double that size, reaching about 34 cm, about the length of a standard school ruler.
• These turtles take five years to reach sexual maturity, then lay three or four clutches each summer (April-June), with each clutch containing one or occasionally two eggs that are roughly 5 × 3 cm and weigh 30 g.
• The species was first recorded on Belitung Island in May 2023, representing a significant range extension between previously recorded populations in Sumatra to the west and Borneo to the east.
• Black marsh turtles were the first turtles discovered to use an XX/XY chromosomal system for sex determination on macrochromosomes, a rare genetic trait in reptiles where temperature usually decides sex.
• In 1999, Malaysia exported about 135,000 black marsh turtles in just ten months, a figure that represents only a fraction of the wild turtles harvested for meat and traditional medicine, highlighting how intense the trade pressure is on this endangered species.

At a glance

About the Black Marsh Turtle

The black marsh turtle, Siebenrockiella crassicollis, is a sleek, almost entirely black freshwater turtle that measures roughly 17 cm in carapace length, though some individuals can double that size. Its ovoid shell bears a pronounced central ridge and often two lateral keels, while the plastron remains unhinged with a shallow U-shaped notch. Thick, dark-gray necks fold into the shell, forming a distinctive collar, and the head sports a short, upward-pointed snout framed by cream-to-yellow markings around the eyes and throat, giving rise to its endearing nickname, the “smiling terrapin.” Favoring slow-moving or stagnant, vegetation-rich waters such as marshes, swamps, and ponds across southern Vietnam, Cambodia, southern Myanmar, Thailand, Malaysia, Singapore, and parts of Indonesia, these turtles spend much of their time buried in soft mud, emerging mainly at night to hunt. Their diet is predominantly carnivorous, capturing insects, worms, molluscs, amphibians, crustaceans, and small fish, though opportunistic scavenging of plant matter and carrion also occurs, especially in adults. A surprising trait for a reptile is its genetic sex-determination system: black marsh turtles possess an XX/XY chromosomal mechanism on macrochromosomes, a rarity among turtles whose sex is usually temperature-dependent. Their nocturnal, shy nature is complemented by a defensive cloacal secretion and powerful, upward-curving jaws that can deliver a firm bite when mishandled.

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