Porifera

The sponges are an ancient group with a fossil record back as far as the Precambrian. There are about 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 millimeters to over two meters across.

Characteristics of Porifera SPONGES HAVE/ARESPONGES DON'T HAVE Body with cells arranged around pores, canals and chambers for the passage of water. An organ system. Skeletal structure of spicules and/or spongin.A nervous system. All aquatic, mainly marine.Much co-ordination between cells. Filter feeders.Tissue organisation, they have some but it is very restricted. Sessile adults; sessile, planktonic larvae.Symmetry, though some are radially symmetrical. Sexual and asexual reproduction.A true body cavity or gut. Gas exchange is by diffusion.

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 spicules. – There are about 500 species. – They occur mainly in deep, cold waters between m, although some can be found below – Some species of Euplectella have a commensal relationship with a shrimp species. A young male and female shrimp enter the central cavity and live there. As they grow they become too large to escape through the sieve-like covering of the osulum, and so spend their entire life inside the sponge. Synconoid and leuconoid canal systems occur in this class.

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. The bath sponges are in this Class, Their skeleton is made of Spongin is a substance similar to the keratin of hair and fur. The barrel sponge, Xestospongia testudinaria, can grow so large that a man can fit inside. They are found growing on solid surfaces, and can reach over 1 m tall and wide. Spongilla lacustris, the pond sponge, is found in fresh still water. It forms a green/yellow growth over stones and plants.

Sponge anatomy…

Sponge structure and defense

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