Preserved colony of bryozoans

• Bryozoans, or moss animals, include over 5000 living species and thousands more are known from their fossils. An individual bryozoan is about 1 mm long and 0.25 mm wide. The animals are colonial and live in interconnected calcite (calcium carbonate) skeletons that form the 'moss'.
• Bryozoans are all aquatic - some live in fresh water (and are sometimes seen in farm ponds) but most live in sea water. They form a crust on rocky surfaces, shells and algae. They are also found on all types of hard surfaces (sand grains, rocks, shells, wood and blades of kelp) and sometimes on sediments. There are 125 different species of bryozoan known to grow on the bottoms of ships. They cause drag and reduce the ability of the fouled ships to manoeuvre. Bryozoans may also grow upon pilings, piers and docks.
• Bryozoans feed on microorganisms such diatoms and other single-celled algae. They trap their food with ciliated feeding tentacles or lophophores (tentacles with cilia that extend like a flower during feeding). A bryozoan's mouth is situated at the base of its tentacles. Bryozoans are preyed on by grazing organisms such as sea urchins and fish, and in fresh water they can be eaten by freshwater snails.
• Bryozoans can reproduce sexually, although budding asexually as the colony grows is the main way a colony expands in size. Bryozoans are hermaphroditic - individuals have ovaries and testes but they usually do not mature at the same time. Some species shed both eggs and sperm into the water but most species brood their eggs and produce free-swimming larvae that disperse to form new colonies.

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