The skeleton (From Greek skeletos = "dried-body", "mummy"), is in biology and in the anatomy 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.
In a figurative sense, skeleton can refer to technology that supports a structure such as a building.
Types of skeletons
Some animals, especially arthropods, and especially insects and crustaceans, have exoskeletons. Exoskeletons are external, as is typical of many invertebrates; they enclose the soft tissues and organs of the body. Exoskeletons may undergo periodic moulting as the animal grows.
Exoskeletons can be made of different materials including chitin (in arthropods), calcium compounds (in corals, mollusks) or silicate (for diatoms and radiolarians).
The exoskeleton of insects is not only a protection but also as a surface for muscle attachment, as a watertight protection against drying and as a sense organ to interact with their environments.
An external skeleton is quite heavy in relation to the volume of an animal, so their presence is only possible in small animals or organisms. The exoskeleton can occur in large aquatic animals because of water pressure. The southern giant clam is a species of extremely large saltwater clam in the Pacific Ocean that has a shell that is 4 m long and weighs about 250 kg.
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