Characters/ Anatomy

Bryozoans are small and often delicate organisms. All bryozoans are colonial and in most cases, the units or zooids of the colony secrete tubes or boxes of calcium carbonate partially encasing the soft parts. Each zooid is basically cylindrical or box-shaped and looks superficially similar to a coral. However, each zooid has a freely suspended gut with both a mouth and an anus and are unquestionably of a higher grade of organisation than corals.

Each tube or box secreted by a zooid of the colony has an orifice, or opening, through which the feeding apparatus (a lophophore) is extended into the water column to gather particulate food matter. In some species, the orifice is covered by an operculum. Key characters are highlighted in the diagrams shown below. Schematic body-plans of the bryzoan Bowerbankia can be viewed by clicking here.

Dr Claus Nielsen (University of Copenhagen) has kindly provided this schematic image (above) of the anatomy of two zooids of a generalised box-shaped bryozoan, showing gut and lophophore (orange, extended and retracted), skeleton, muscles, funicular system, communication pores, ovary (left zooid) and an ovicell with developing larva.

Dr Claus Nielsen (University of Copenhagen) has kindly provided this schematic image of the anatomy of two zooids of a cyclidrical bryozoan, showing gut and lophophore (orange, extended and retracted), skeleton, muscles and communication pores.

Author: Luke Mander
Last updated: 20.11.05
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