Bryozoans

Several colonies of the bryozoan Fenestella, of Permian age. Source: Museum Victoria.

The fossils of these tiny marine animals often occur in vast numbers and are a major component of certain types of limestone. The animals live in colonies of hundreds of individuals (zooids) which secrete cylinders of lime about 2 mm long in which their soft parts are enclosed.

A ring of about 10 tentacles can be extended out of the end of the cylinder to direct food into the animal's mouth.

Because fossil bryozoan colonies look like lace, the animals are sometimes called sea lace (also sea moss or moss animals).

Bryozoan Archimedes wortheni from the Carboniferous of Illinois, USA. Source: Museum Victoria.

Bryozoans first appeared in the Ordovician Period (434 to 490 million years ago) and quickly became abundant. Many species disappeared in the mass extinction at the end of the Permian Period (about 251 million years ago), but those that survived were able to recolonise the oceans.

Over 15000 fossil species are known, and the 3500 species which are living today are widespread in all oceans, particularly the western Pacific. They are found at all depths, but particularly favour depths between 20 and 80 metres, where they encrust rocks, seaweed and coral reefs. Bryozoan limestone is found in many locations in Victoria, including Point Addis near Torquay, and at Fyansford near Geelong.