PORIFERA (Sponges)
Porifera means "pore bearer" and is the scientific name for sponges. They are considered simple animals as they consist of many cell types with special functions and they lack tissues and organs. Their skeleton can be composed from two materials: spongin (a soft, flexible organic material - made of the protein collagen) and spicules (small rods of calcium carbonate or silica).
Sponges are sessile animals, they live permanently affixed at the base and do not move around as adults. As a result, they are unable to move to escape predators, but discourage attack with strong chemicals and an exterior of bristly textures.
They feed by pumping large quantities of water (hundreds of litres per day) through their bodies and filtering out tiny organisms and dead plant and animal particles as food. This passage of water also brings in oxygen and takes out carbon dioxide and wastes.
Sponges exist in all different shapes, sizes and colours, and members of the same species can vary greatly depending upon where they live. Sponges occur in marine and freshwater but do not occur on land.
There are three classes of sponges existing now (other classes have become extinct and are found in the fossil record):
Calcarea Typically pale in colour and with a tendency to be quite small in size (less than 30cm), this class of sponges lacks spongin; their skeletons are composed entirely of calcium carbonate and as a result they are quite brittle to touch. They are usually found in shallow water. |
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Demospongiae (Demosponges) The demosponges comprise 95% of the world's sponges and include the most colourful species. They range in size from small, encrusting forms to large irregular masses. They have spicules of silica dioxide and/or spongin. These are the sponges most commonly seen whilst diving or walking along the shore. Unlike the other four classes whose members are all marine, demosponges can also be found in freshwater. |
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Hexactinellida Named for their siliceous skeletons, glass sponges lack an outer layer, and have spicules that form a latticework. They are usually cylindrical, or funnel-shaped. Most species live in deep waters. |
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