Cheloniidae (marine turtles; order Chelonia, suborder Cryptodira) A family of turtles in which the shell consists of a carapace which is flat and streamlined, and a plastron which is reduced. The fore limbs are broad and flat, with one or two claws. The hind limbs are flattened and rudder-like. Neither the head nor legs retract into the shell. These turtles are mainly carnivorous, although Chelonia mydas (green turtle) is basically herbivorous, occasionally eating molluscs and crustaceans. There are five species, with a cosmopolitan distribution in warm seas. Caretta caretta (loggerhead turtle) has a chestnut-coloured carapace up to 1.3 m long and a yellowish plastron; it occurs in all warm seas and occasionally reaches Britain. Eretmochelys imbricata (hawksbill turtle), the smallest member of the family (up to 90 cm long), has multicoloured, translucent carapace scales, overlapping towards the back, used in the oriental tortoiseshell industry. Marine turtles come ashore only to lay eggs.

Chelonia (Testudines; turtles, terrapins, tortoises; class Reptilia, subclass Anapsida) An order of reptiles in which the body is enclosed in a shell of bony plates covered by horny scales with an upper carapace and lower plastron. The carapace is often fused to the vertebrae and ribs. The jaws are toothless and horny. There are some 250 species, including marine, freshwater, and terrestrial forms.