What are bryozoans?

Educational value

• Bryozoans, sometimes known as moss animals, are an exclusively aquatic phylum of about 6000 species, with all but about 50 species living in marine environments. The adults of most species are sessile - they are attached to the sea floor - usually in shallow water, but some are found at great depths in the oceans. They feed on microscopic plankton and other particles floating in the water, and are in turn preyed upon by fish, crustaceans, sea stars and sea urchins.
• Most bryozoans are colonial, consisting of numerous connected individuals known as zooids, each about half a millimetre long. The feeding zooids, known as autozooids, have a crown of tentacles surrounding their mouths and these are at the end of a flexible tube that can be extended from the zooid body. The tentacles filter particles of food from the water.
• Bryozoan colonies can be from 1 cm to more than a metre across and often have a branching, plant-like appearance. A group of bryozoan colonies growing together is known as a thicket. In cool waters, thickets provide places for marine animals to shelter and hide, serving the same function as coral reefs and algae in warmer regions.
• In bryozoan colonies, each zooid secretes an exoskeleton that protects its body and supports the colony. In some species the skeleton is made of chitin or protein; in others it is made of the mineral calcium carbonate. Marine animals will be less able to incorporate this mineral into skeletons as the oceans acidify due to absorption of increased atmospheric carbon dioxide, so bryozoans may act as an early warning system for marine ecosystems.

Year level

5; 6; 7; 8; 9

Topics Filter feeding Invertebrates Marine habitats