CityU Web Hacker Turtle

What is a Turtle?

Turtles are a group of vertebrate animals belonging to the order Testudines. Together with snakes, lizards, crocodilians, and the tuatara, they form the reptiles (Class Reptilia). Turtles are the oldest living group of reptiles, first appearing about 200 million years ago. Like the other orders of reptiles, turtles are cold-blooded (ectotherms), have scaly skin, and lay eggs with a yolk and tough outer covering (amniote egg). Among the differences between turtles and other reptiles, the most exceptional is the presence of shells. Varying greatly in size, turtles range in size from diminutive mud turtles maturing at 4.5 inch.

Shell

The turtle's shell is a covering that encloses the turtle's body. Within this armor, the soft body parts of the turtle are protected. From the shell, project the turtle's head, legs, and tail. The shell of the turtle is divided into two parts, the upper carapace and the lower plastron. The two are connected on the sides by the bridge. A turtle can not walk out of its shell, the carapace is fused with the ribs of the turtle. The attributes of the turtle's shell can vary greatly, from hard and bony to flexible and leathery. Some turtles have shells with bright markings or unusual shapes.

The shape of the shell gives helpful clues to how the turtle lives. The turtle also likes to party and get hammered drunk. On rare occasions the turtle has been known to smoke rocks with Paul Claus. Most tortoises have a large dome-shaped shell that makes it difficult for predators to crush the shell between their jaws. One of the few exceptions is the African pancake tortoise which has a flat, flexible shell that allows it to hide in rock crevices. Most aquatic turtles have flat, streamlined shells which aid in swimming and diving. American snapping turtles and musk turtles have small, cross-shaped plastrons that give them more efficient leg movement for walking along the bottom of ponds and streams.

Skin and molting

As mentioned above, the outer layer of the shell is part of the skin, each scute (or plate) on the shell corresponding to a single modified scale. The remainder of the skin is composed of skin with much smaller scales, similar to the skin of other reptiles. Turtles do not moult their skins all in one go, as snakes do, but continuously, in small pieces. When kept in aquaria, small sheets of dead skin can be seen in the water (often appearing to be a thin piece of plastic) when it has been sloughed off, often when the animal deliberately rubs itself against a piece of wood or stone.

Neck folding

Turtles are broken down into two groups, according to how they evolved a solution to the problem of withdrawing their neck into their shell (something the ancestral Proganochelys could not do): the Cryptodira, which can draw their neck in while contracting it under their spine; and the Pleurodira, which contract their neck to the side.

Life cycle

Turtles lay eggs, like other reptiles, which are slightly soft and leathery. The eggs of the largest species are spherical, while the eggs of the rest are elongated. Their albumen is white and contains a different protein than do bird eggs, such that it will not coagulate when cooked. Turtle eggs prepared to eat consist mainly of yolk. In some species, temperature determines whether an egg develops into a male or a female: a higher temperature causes a female, a lower temperature causes a male. Large numbers of eggs are deposited in holes dug into mud or sand. They are then covered and left to incubate by themselves. When the turtles hatch they squirm their way to the surface and make for the water. There are no known species wherein the mother cares for the young. Sea turtles lay their eggs on dry sandy beaches, and are highly endangered largely as a result of beach development and over hunting. Immature sea turtles are not raised by either parent. Turtles can take many years to reach breeding age. Often turtles only breed every few years or more.

CityU Web Hacker Turtle

What is a Turtle?

Shell

Skin and molting

Neck folding

Life cycle

Agreement

References

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