Skeleton

The skeleton (from Greek σκελετός, skeletós "dried up") is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body. There are also two other forms of skeleton referred to, the hydroskeleton and the cytoskeleton.

Types of skeletons

Exoskeleton

Exoskeletons are external, and are found in many invertebrates; they enclose and protect the soft tissues and organs of the body. Some kinds of exoskeletons undergo periodic moulting as the animal grows, as is the case in many arthropods including insects and crustaceans. Exoskeletons are made of different materials including chitin (in arthropods), calcium compounds (in stony corals and mollusks) and silicate (for diatoms and radiolarians.)

The exoskeleton of insects is not only a protection but also serves as a surface for muscle attachment, as a watertight protection against drying and as a sense organ to interact with their environments. The shell of mollusks also performs all of the same functions, except that in most cases it does not contain sense organs.