Thursday, February 21, 2013

Turtles & Terrapins (Phylum Chordata: Order Testudines) of Singapore

Turtles (phylum Chordata, subphylum Vertebrata, superclass Tetrapoda, class Reptilia, order Testudines or Chelonii) are air-breathing reptiles with four limbs, a tail, and an external shell modified from their ribs. The shell comprises a shield-like carapace on their back and a flat bony plate (plastron) protecting their bellies. When disturbed, they can either completely or partially withdraw the head, limbs and tail into the shell for protection.

The terms used to describe the various types of turtles can be confusing, but generally, the term "terrapin" refers to a turtle that is semi-aquatic, the term "tortoise" is used for land-dwelling species, while a "soft-shelled turtle" has a shell covered with soft, leathery skin.

Like most other reptiles, turtles have limited physiological means to maintain the body temperature within a narrow range, and are more reliant on external heat sources. However, some of the larger turtles have high metabolic rates, and hence they tend to have higher body temperature than their surrounding environment. Like other vertebrates, they have a backbone with a spinal cord (a hollow tube of nervous tissue). This backbone is fused to part of the carapace.

Turtles have separate sexes. The males will mate with the females, after which the females will lay the eggs in holes they have dug into the ground. The eggs will then be buried and left to incubate.

Here are some of the turtles that can be found in Singapore:

Family Cheloniidae

Cheloniid turtles are sea turtles with a hard shell and paddle-like limbs. The shell is relatively flat, giving the animal a streamlined shape. The shell is covered with horny, scale-like plates called scutes, while the head and limbs are partially covered with thin scales. The neck can only retract partially into the shell. They usually have a beak. Sea turtles are very much threatened by fishing activities, as many get trapped underwater by fishing nets. Being air breathing, they can suffocate to death underwater. Both the turtles and their eggs are exploited for food by locals. Interestingly, sea turtles can migrate long distances (up to a few thousand kilometres) between their feeding grounds to the sandy beaches where they are hatched to lay eggs. The females will crawl onto the beach at night, dig a nest into the sand, lay the eggs, bury them with sand, and leave them for incubation. The hatchlings will emerge within a few months. Many of them are eaten by predators on the beach and in the shallow water, and few will survive to adulthood.

Hawksbill Turtle (Eretmochelys imbricata)
The Hawksbill Turtle (Eretmochelys imbricata) is an internationally critically endangered sea turtle which usually inhabits coral reefs, lagoons, bays and estuaries. It feeds on sponges, algae, corals and molluscs. The carapace, which can get to about 1m long, is olive-brown in colour.

Hawksbill Turtle (Eretmochelys imbricata)
The Hawksbill Turtle can be differentiated from other sea turtles by its pointed bird-like beak, and two pairs of scales on its forehead between the eyes behind the beak.

Green Turtle (Chelonia mydas)
The Green Turtle (Chelonia mydas), on the other hand, only has a pair of longish scales on its forehead between the eyes behind the short and broad beak.

Green Turtle (Chelonia mydas)
The carapace, which can get to about 1.4m long, is olive or brown with radiating dark patterns. Green turtles are internationally endangered, and are usually found in tropical areas around islands and along coast with sandy beaches. The juveniles are carnivorous, while the adults feed on seagrass and seaweeds.

Family Trionychidae

Trionychid turtles are usually called softshell turtles, due to the soft carapace which is covered with a layer of leathery skin. They have three claws on their fully webbed feet, a long neck, and a tube-like snout with the nostrils at the tip. Although they may leave the water sometimes to bask in the sun, they are usually hidden in soft substrates, with their heads partially exposed to snap at the small animals in the water. They breathe by extending their necks regular to put the nostrils above the water. They can give very nasty bites, and hence should not be handled.

Juvenile Malayan Forest Softshell Turtle (Dogania subplana)
The Malayan Forest Softshell Turtle (Dogania subplana) has a smooth, flat and leathery carapace which can grow to about 35cm long. It is roughly oval-shaped and yellowish-brown in colour. The above photo features a juvenile, which has several black, eye-like spots on its carapace. The adults lack the obvious spots, but has blurry darker patches instead. The carapaces of both juveniles and adults are marked with irregular darker streaks and a darker stripe in the middle. They are usually found in clear streams with sandy bottoms in mature forests.

The Chinese Softshell Turtle (Pelodiscus sinensis) is native to China and Japan, but has been introduced to ponds and reservoirs probably through religious merit-making offerings. The carapace is oval-shaped, smooth and leathery, either uniformly brown or with pale and dark spots. There is a ridge at the front edge of of the carapace. The head is marked with black streaks radiating from the eyes, and a pale stripe marks the sides of the neck. This species is commercially bred in the region for consumption, and can grow to about 35cm long.

Family Emydidae

Emydid terrapins are not native to the region, but as several species are popular in the pet trade, they have been widely introduced to many countries out of their native range. They have an oval to oblong domed carapace with 11 pairs of peripheral scutes around the margin. These terrapins are usually found in freshwater environment, at least in some part of their lives. They are mostly omnivorous.

Red-eared Slider (Trachemys scripta)
The Red-eared Slider (Trachemys scripta) is native to North America, and the ones found in local water bodies are either escaped or abandoned pets (by irresponsible pet owners), or those released as religious merit-making offerings. The domed carapace, which is olive brown with yellowish streaks, can get to about 28cm long. The head is green with many yellow stripes, and a reddish band is located behind the eye. This diurnal and omnivorous species is mostly aquatic, though they can be seen basking in the sun sometimes.

Family Geoemydidae

Geoemydid terrapins are rather similar to the previous group, with an oval to oblong carapace with 11 pairs of peripheral scutes around the margin. The carapace can be depressed or domed. These terrapins can withdraw their necks into the shell. Most species are omnivorous, though some may begin as carnivorous juveniles, but become herbivorous as they mature.

Malayan Box Terrapin (Cuora amboinensis)
The Malayan Box Terrapin (Cuora amboinensis) has a highly domed black carapace which can get to about 25cm long. The carapace has a smooth margin, and in its middle are five vertebral scutes. The head is black above, with a bright yellowish stripe on both sides. This terrapin is semi-aquatic to terrestrial, and can be found in agricultural areas and the edge of forests. It can be active both in the day and at night. While the Malayan Box Terrapin is native to Singapore, most of the ones seen in our reservoirs and ponds in parks are probably released illegally for religious merit-making offerings.

The Giant Leaf Terrapin (Heosemys grandis), also known as the Giant Asian Pond Turtle, is native to continental Southeast Asia, but is probably introduced to the ponds and reservoirs in Singapore through religious merit-making offerings. This big terrapin can grow to about 50cm long. It can be recognised by the blunt snout and greyish carapace.

Chinese Stripe-necked Turtle (Mauremys sinensis)
The Chinese Stripe-necked Turtle (Mauremys sinensis) is native to China, Taiwan and Vietnam. This species can sometimes be seen in ponds, probably released illegally for religious merit-making offerings. It can be recognised by the yellow stripes on its neck.

  • Baker, N. 2013. Ecology Asia. Retrieved Feb 12, 2013, from
  • Baker, N. & K. Lim, (Vertebrate Study Group, Nature Society Singapore). 2008. Wild Animals Of Singapore. Draco Publishing and Distribution Pte. Ltd. 180 pp.
  • Das, I. 2010. A Field Guide to the Reptiles of South-east Asia. New Holland Publishers (UK) Ltd. 376 pp.
  • Fritz, U & P. Havaš. 2007. Checklist of Chelonians of the World. Vertebrate Zoology 57 (2): 234.
  • Lim, K.P. & L. K. Lim. 1992. A Guide to the Amphibians & Reptiles of Singapore. Singapore Science Centre. 160 pp.
  • Marques M., R. 1990. FAO Species Catalogue, Vol. 11. An Annotated and Illustrated Catalogue of Sea Turtles of the World. Rome. Food and Agriculture Organization of the United Nations. 81 pp.

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