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Encrusted sponges
Cup sponges Wall sponges
Ball sponges Tree & Fan sponges
Tubular  sponges
Other sponges    

The sponges are an ancient group with a fossil record back as far as the Precambrian. There are about 10 000 known species of marine sponges, and about 150 freshwater sponges. They are relatively abundant in all marine waters at all depths. They vary in size from a few millimetres to over two metres across.

Their cells are structured around a system of pores, chambers and canals through which water is moved by the action of the flagellae of the choanocyte cells. The large pores called oscula (singular - osculum) are water outlets, and the small pores called ostia are water inlets.

Sponges is grouped into four classes

Class Hexactinellida

These are commonly known as the glass sponges . They are often radially symmetrical and vase- or funnel-shaped and can be up to 1 m across and 1 m high, and are very beautiful. Their distinguishing feature is the network formed by the six-rayed siliceous spicules. There are about 500 species. They occur mainly in deep, cold waters between 200 - 2000 m, although some can be found below 6000. 

Class Calcarea

As the name suggests sponges in this class have spicules of calcium carbonate. The spicules are either free or fused. They tend to be relatively small, mostly less than 10 cm, and tubular or vase-shaped. All three types of canal system occur in this class. There are about 100 species, mainly marine in water no deeper than 1000m.

Class Demospongiae

This is the largest Class containing over 90% of living sponges, and nearly all the larger species. They can be found at all depths in both fresh and salt water. The skeleton can be siliceous, spongin, or both. The spicules are either simple or four-rayed. All have the leuconoid canal system. Demospongiae are often brightly coloured.

Class Sclerospongiae

This is a small group of sponges that resemble corals. They are usually found in dark tunnels in coral reefs. The skeleton consists of siliceous spicules and spongin on a thick basal layer of calcium carbonate. All in this class have the leuconoid canal system. 


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