turtle

The matamata is a South American turtle. Its body is camouflaged to ambush prey – the head is flattened like a leaf, the neck thick with flaps of skin, and the shell heavily sculpted.

Freshwater or marine reptile whose body is protected by a shell. Turtles are related to tortoises, and some species can grow to a length of up to 2.5 m/8 ft. Turtles often travel long distances to lay their eggs on the beaches where they were born. Many species have suffered through destruction of their breeding sites as well as being hunted for food and their shells. Unlike tortoises, turtles cannot retract their heads into their shells.

Marine turtles are generally herbivores, feeding mainly on sea grasses. Freshwater turtles eat a range of animals including worms, frogs, and fish. They are excellent swimmers, having legs that are modified to oarlike flippers but which make them awkward on land. The shell is more streamlined and lighter than that of the tortoise.

Species include the green turtle Chelonia mydas; the loggerhead Caretta caretta; the giant leathery or leatherback turtle Dermochelys coriacea, which can weigh half a tonne and grow up to 2.5 m/8 ft; and the hawksbill Eretmochelys imbricata, which is hunted for its shell which provides tortoiseshell, used in jewellery and ornaments, and is now endangered. Other turtles suffer because their eggs are taken by collectors and their breeding sites are regularly destroyed, often for tourist developments. The world's rarest turtle is the Kemp's ridley, which breeds only at a single site in the Gulf of Mexico. The total population is less than 10,000 (1998).

A new species of turtle was discovered in Mexico in 1997. It has been named Kinosternon chimalhuaca.

The use of radiotransmitters has shown that migrating leatherback turtles navigate by following the contours of the Earth's crust along existing pathways. The identification and protection of these pathways could substantially reduce the number of leatherback turtles drowned in driftnets or caught on fishing lines.

Unusually in turtles, the eggs of the leatherback are not uniform in size. The female lays as many as 12 clutches of around a hundred eggs and each clutch contains a number of tiny yolkless eggs that serve to space the eggs when buried a metre down in the sand to allow air circulation. Only one in a thousand baby leatherbacks will survive to adulthood.

Leatherbacks lack the hard shell of other turtles, having instead a thick layer of cartilage reinforced by thousands of small bones.

turtle

Small computer-controlled wheeled robot or a representation of it on a computer monitor. The turtle's movements are determined by programs written by a computer user, typically using the high-level programming language LOGO. Programming a turtle is one way to learn programming logic and the use of procedures.