An Alaska marine bryozoan, showing the contrast of colony shapes. (Photo by Aaron Baldwin)

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Each little bryozoan creature (called a zooid) is less than a millimeter long, bearing a set of retractable tentacles for filter-feeding. They catch even tinier particles in the water or sweep them in on water currents. Those particles pass through the digestive tract; some species even have a muscular gizzard, for crunching diatoms (unicellular algae that have shells of silica). Waste products are eliminated from an anus that lies outside of the bases of the tentacles. Individual zooids are typically housed in a body wall of chitin or calcified materials or, in some freshwater species a gelatinous layer. There are pores in the body walls and body fluids can pass from one individual to another nearby. The feeding apparatus and digestive tract may periodically degenerate, which gets rid of accumulated country wise email marketing list waste products (there is no kidney system), sometimes making room for eggs, and are later replaced by regenerated parts.


Many marine species have polymorphic zooids: in addition to the common ones that feed, there are non-feeding ones that are fed by the others as nutrients are passed among individuals. Some of these have sharp little forceps-like beaks, which can be used to pinch and toss off unwanted small creatures that drift in. Others have long “whiskers” for sweeping away sediment and even, in some species with very small colonies, for walking over the substrate (with very small steps).