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, see Spongia sp. left. Bath sponges are simply the spongin skeleton which has been left behind after all the other cells have been removed in various treatments. Spongin is a substance similar to the keratin of hair and fur. Bath sponges do not have siliceous spicules.
The barrel sponge, Xestospongia testudinaria, left is also in the demospongiae. It 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.
Callyspongia plicifera, the Tubular sponge, right, is found in the Caribbean coral reefs at a depth of 7 - 25 m. It is also sometimes known as the Azure vase sponge. Live specimens are beautifully coloured from pink through the blues into purple. As can just be seen in this photograph of a preserved specimen, the inner walls are very smooth in contrast to the outer walls. They tend to grow in small groups of 2 or 3, and can reach a height of 27 cm with a diameter of 13 cm.
Below is Callyspongia ramosa, the Finger sponge. It is found in New Zealand from intertidal to 50 m deep.
On the left is Spongilla lacustris, the pond sponge. It is found in fresh still water. It forms a green/yellow growth over stones and plants. The colour varies according to the light level, with the greener sponges growing in good light.
Breadcrumb sponge, Halichondria panicea, right, is found in temperate waters around the U. K. and Ireland, the Mediterranean and North Atlantic, on shore, in rock pools, under stones, on kelp holdfasts and algae, and it has been found as deep as 500 m.
It can be up to 20 cm thick and 60 cm across. The thickness depends mainly on roughness of wave action, with the thicker specimens being found in the more sheltered locations. The colours vary from olive green to orange and yellow cream.