Exoskeleton

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An exoskeleton is an external skeleton that supports and protects an animal's body, in contrast to the internal skeleton (endoskeleton) of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Some example of exoskeleton animals include insects such as grasshoppers and cockroaches, and crustaceans such as crabs and lobsters. The shells of the various groups of shelled mollusks, including those of snails, clams, tusk shells, chitons and nautilus are also exoskeletons.

Mineralized exoskeletons first appeared in the fossil record about 550 million years ago, and their evolution is considered by some to have played a role in the subsequent Cambrian explosion of animals.[citation needed]

Some animals, such as the tortoise, have both an endoskeleton and an exoskeleton.

Contents

Role of the exoskeleton

Exoskeletons contain rigid and resistant components that fulfil a set of functional roles including protection, excretion, sensing, support, feeding and acting as a barrier against desiccation in terrestrial organisms. Exoskeletons have a role in defence from pests and predators, support, and in providing an attachment framework for musculature.[1]

Exoskeletons contain chitin and when calcium carbonate is added, the exoskeleton grows in strength and hardness.[citation needed]

Diversity

Many taxa produce exoskeletons, which are composed of a range of materials. Bone, cartilage, or dentine is used in the Ostracoderm fish and turtles. Chitin forms the exoskeleton in arthropods including insects, arachnids such as spiders, crustaceans such as crabs and lobsters (see arthropod exoskeleton), and in some fungi and bacteria. Calcium carbonates constitute the shells of molluscs (see Mollusc shell), brachiopods, and some tube-building polychaete worms. Silica forms the exoskeleton in the microscopic diatoms and radiolaria.

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