Invertebrates
Bryozoan
Bryozoa · also called moss animals, sea mats
A bryozoan colony is not one animal but thousands of them, each barely visible on its own, packed into tiny individual chambers and working together so closely that some species even assign different jobs to different members — feeding to some, defence or reproduction to others — much like a colony of social insects.
Overview
Bryozoans, phylum Bryozoa, are colonial filter feeders found in marine and some freshwater habitats worldwide. Each tiny individual, or zooid, extends a tentacled feeding structure called a lophophore from its own chamber, and the name, meaning “moss animal,” reflects the finely textured, often moss-like look of many colonies.
One colony, many shapes, many jobs
Colonies range from thin encrusting sheets to upright, branching, plant-like forms, and in some species zooids specialise into distinct roles rather than all feeding identically — a genuine division of labour among genetically identical colony members. The group’s well-preserved fossil chambers also give bryozoans an excellent, geologically useful fossil record spanning several hundred million years.
Status
Least Concern — abundant and diverse worldwide, though certain species are persistent biofoulers on ship hulls and aquaculture equipment.
Bryozoan: common questions
Are bryozoans the same thing as coral?
No, although bryozoan colonies and coral colonies can look superficially similar, both being built from numerous small individual animals sharing a common structure, they belong to entirely separate and unrelated animal groups. Bryozoans feed using a specialised tentacled structure called a lophophore and are more closely related to certain other lophophore-bearing invertebrate groups, while corals are cnidarians, more closely related to jellyfish and sea anemones, and use stinging tentacles rather than a lophophore to capture prey, making the resemblance between bryozoan and coral colonies a case of superficial similarity rather than close relationship.
How do the individual animals in a bryozoan colony work together?
Each individual animal, called a zooid, lives in its own small chamber but remains physically connected to its neighbours within the colony, and in many species some level of coordination or even genuine division of labour occurs, with certain zooids specialising in feeding while others take on more specialised roles such as colony defence or reproduction rather than everyday feeding. This cooperative, colony-wide organisation allows a bryozoan colony to function in some ways more like a single, complex, cooperative organism than as a simple aggregation of separate individual animals.
Why do bryozoan colonies have such different shapes?
Colony shape in bryozoans is strongly influenced by species-specific growth patterns combined with the physical environment and specific surface a given colony is growing on, resulting in a wide range of forms from thin, flat, encrusting sheets that hug the contours of a rock or shell to upright, branching, plant-like structures that project into open water to maximise the colony's filter-feeding surface area. A small number of bryozoan species have even evolved compact, mobile, free-living colonies capable of limited movement rather than remaining permanently attached to a single fixed surface.
Do bryozoans cause any real problems for human activities?
Yes, certain bryozoan species are effective and persistent colonisers of ship hulls, aquaculture equipment such as nets and cages, and other submerged human-made structures, contributing to a broader problem called biofouling that can significantly increase drag and fuel consumption for vessels and clog or damage aquaculture and industrial equipment. Managing bryozoan and other biofouling growth is an ongoing, genuine practical and economic concern for the shipping and aquaculture industries in many parts of the world.