The bryozoan shown in the image, Fenestella, was fan-shaped.

© Great Barrier Reef Marine Park Authority

This living Reteporellina bryozoan colony looks very similar to Fenestella, with delicate branching fronds.

Bryozoans, or ‘moss-animals’ are colonial animals which are common in shallow seawater. They build colony skeletons of calcium carbonate. Although the individual animals are very tiny, they are quite complex with nervous systems and feeding organs. The colonies can be fan-shaped or branching, or can encrust other organisms such as seaweed.

Bryozoans are filter feeders. The bryozoan animal (zooid) feeds by extending feather-like filters into the water around it. These filters catch tiny plankton and other particles of food as they drift past.

Bryozoans were very important parts of the Wenlock Reef, ‘baffling’ and trapping sediment in their skeletons. After they died, new reef developed over the old skeletons.

Bryozoans first appeared in the Ordovician, and are common in seas today.