Sponges

Sponges are simple colonial animals. They have no real organs and their body tissue is made up of fibre-like protein, which is just like a bath sponge. The sponge gets its structure from hard, multi-pointed rods called spicules. Each species has uniquely shaped spicules. Made from silica or calcium carbonate, the spicules protect the sponge from predators because a mouthful of sponge would be like a mouthful of splinters.

Sponges feed by filtering tiny food particles from the current of water that they create around themselves. They use specialised cells that have paddle-like cilia. The beating of these cilia can pump the equivalent of four to five times the sponge's volume of water every minute.

Most coastal waters will have sponges present all year round but they are also found in intertidal pools.

Sponge facts

• There are around 10,000 species of sponges worldwide.
• About 160 species are found in the Sydney region.
• A single species of sponge may have different forms, so identification may depend on the spicule shape, which is unique to species.
• Most carnivorous animals avoid sponges as they are of poor nutritional value and are protected by spicules and toxins.
• Sponges are generally hermaphroditic, which means they produce both sperm and eggs.
• Sperm from neighbouring sponges are drawn in to fertilise eggs, which become larvae that swim away to colonise new areas.