Types of Skeletons

The main kind of skeletons in animals are the

• hydrostatic skeleton,

•exoskeleton, and

• endoskeleton.

Hydrostatic skeleton

Soft bodied animals like  the earth worm use fluid pressure to provide support. These tubular animals have a muscular body. The fluid is secreted to fill the spaces in the body. The fluid presses against the muscular body wall, causing the muscles to contract, exerting a force against the fluid. This helps to maintain the shape and form of the animal and is known as a hydrostatic skeleton.

Exoskeleton

Arthropods are supported by a skeleton of non living material which forms on the outside of their bodies. This outer skeleton is known as an exoskeleton. It is secreted by the cells covering the body of the animal. The main components is chitin which is often strengthened by deposits of protein and minerals, especially calcium carbonate. Calcareous exoskeleton , common in aquatic crustaceans like crabs and prawns, are hard and heavy.

    Exoskeleton is made up of a series of plates or tubes attached as joints by sheets of unmodified chitin. This makes the exoskeleton flexible, which is important for movement. The living animal is attached tot he exoskeleton by muscles. Thus, the exoskeleton supports the animal against gravity, and at the same time, together with muscles, enables the animal to move about.

    Animals with exoskeleton moult periodically. They shed their old exoskeletons and grow rapidly in size, while the exoskeletons are still soft and extensible. Moulting is also known as ecdysis.

Endoskeleton

An internal skeleton, known as an endoskeleton, ja found in all vertebrates. with the exception of cartilaginous fishes, the endoskeleton of vertebrates are composed mainly of bones. Unlike exoskeleton, bones are living tissues. They can grow steadily as the animal grows so that Moulting is not necessary.

   Jones of many shapes and sizes make IP the endoskeleton of vertebrates. These bones are attached together at movable joints by tough flexible fibres called ligaments. This makes the skeleton flexible. Muscles are attached to the bones. Together, muscles and bones , bring about bodily movements and locomotion.