Article | Updated 9 months ago
Sponges (Phylum: Porifera) are the simplest animals on the planet and were once considered plants by scientists. They are multi-cellular animals but do not have any form of tissues or organs.
The skeleton of sponges is usually made up of protein fibres known as spongin. In a number of sponge species this protein also contains rod-like structures (spicules) made of calcium carbonate or silica dioxide.
Adult sponges are a sessile group of animals. This means that they are fixed to the ocean floor and therefore cannot move freely to capture food. They are filter feeders and obtain their food as water passes through the network of canals that make up their bodies.
Sponges provide a safe habitat for other animals including small crabs and brittle stars.
Although the sponges found washed up on beaches are dull in appearance, live sponges are normally vividly coloured. There are at least 15 000 species of sponges worldwide and within the Dampier Archipelago 275 species have been recorded.
Calcareous Sponges (Class: Calcarea) are distinguished by a skeleton composed entirely of calcium carbonate spicules. This makes them quite brittle compared to other sponges. Calcareous sponges also lack spongin, protein fibres.
These sponges are often pale in colour and quite small, generally less than 30 cm. Calcareous sponges are typically found in shallow water and only inhabit marine environments.
Demosponges (Class: Demospongiae) are the most commonly seen sponges when snorkelling, diving or walking along the beach. This group contains 95% of the world's sponges. Demosponges include the most colourful species and range in size from small encrusting forms to large irregular masses.
Unlike other sponges, demosponges can also be found in freshwater habitats.
The skeleton of these sponges can include a protein known as spongin. There are various types of spongin, some of which form fibres to build the skeletal framework. Some demosponges also have spicules made of silicon dioxide.
Glass sponges (Class: Hexactinellida) are so named as they possess a skeleton made of silicon dioxide. Silicon dioxide is a substance used to manufacture glass. Glass sponges are generally cylindrical or funnel-shaped and grow to between 10 and 30 cm.
Sponges belonging to this group are found in marine waters at great depths. They have been reported from 5 - 6 770 m depth and about 500 species are known although twice this number are thought to exist but have not yet been described.