These are generally confined to tropical and warm temperate waters. They are characterised by having well developed paddle-shaped limbs without obvious ankle joints. Sea turtles can swim at considerable speeds. Their nostrils are positioned on top of the snout as with other aquatic and marine reptiles. The shell, which is often covered in algae and barnacles, is very strong and consists of bony plates (modified scales). Mating occurs at sea and females come ashore at night on a rising tide to lay their eggs. These are laid in a hole excavated on a sandy beach. Many of the eggs and hatchlings fall prey to predators. Most of the species inhabiting the Australian waters are known to breed at specific sites along our northern coastline.
Although some species of sea turtles naturally occur here, they are not often seen in our waters. None are known to breed this far south. The 4 species observed locally, are the Green Turtle (Chelonia mydas), Loggerhead (Caretta caretta), Hawksbill (Eretmochelys imbricata) and the Luth or Leathery Turtle (Dermochelys coriacea) which is the world's largest, attaining 2.4 metres in length. Placed in a family on its own (Dermochelyidae) it has a unique shell made up of very small plates embedded in a leathery skin rather than a fused bony shield.
A family of aquatic and semi-aquatic reptiles found also in New Guinea and South America. They belong to a group described as pleurodirous or side-necked turtles. It refers to the way they retract the head by folding the neck into a horizontal groove under the front edge of the upper shell. This differs from other freshwater turtles which fold the head into an S-shape to withdraw it under the shell. The limbs can also be withdrawn to some extent. All have distinct ankle joints, webbed feet and 4 or 5 claws.
The term "terrapin" is used in North America for some of their turtles/tortoises
We refer to the members of this family as turtles because of their webbed feet and aquatic behaviour. The term "tortoise" is used for the dome-shelled, predominantly land based tortoises, such as those found on the Galapagos Islands.
Male turtles have much longer tails than females. Worrell (1963: 12) describes courtship as ".....an uncomplicated affair; the male circles the female and occasionally strokes her face gently with a fore-foot. Mating takes place under the water". The eggs, when laid, are white and brittle-shelled.
Sixteen species occur in Australia, two occur in the Perth region of Western Australia.