Sponges

Sponge / Phylum Porifera

Tube Sponge / Theonella cylindrica / Family Theonellidae / Phylum Porifera

The Great Barrier Reef is home to about 1500 species of sponge - or about 30 per cent of the Australian sponge fauna.

Sponges fulfill several important roles on the Reef:

• some live off the products of symbiotic cyanobacteria
• others live off the detritus and waste products that filter down through the water column
• sponges also comprise the major part of the diet of the endangered hawksbill turtle

Sponges are common and often colourful reef animals. They are bottom-dwelling (benthic animals) and are often confused with plants because their simple bodies can take on almost any shape. Some are simple vase-like or tube-like growths. Others may form colourful crusts over rubble or dead coral. They also can form growths that look like hands, fans or shrubs.

Whatever their shape, all sponges are built on the same lines - a hollow structure with a body wall built around a skeleton made of thousands of minute limestone or glassy structures called spicules. The outer wall of a sponge has many small holes (pores) through which water is drawn by the living cells inside. These cells feed by trapping minute food particles that are carried past by the water. The water then passes out through larger holes in the body wall.