Bryozoa are a phylum of aquatic animals that live by filtering food from the water. Their name means 'moss animal', and modern bryozoans are mainly confined to warm (tropical) waters. Individual animals (called zooids) are typically tubes of one form or another, less than a millimetre in length. Bryozoan are colonial, however, and grow into masses that may be up to a metre in length; more commonly, colonies are measured in terms of a few centimetres. As colonies, they take three forms: branching, encrusting and fan-like (see image, right). Bryozoans are especially interesting to study because they are very sensitive to the environmental conditions in which they live, so give a good indication of the local environment.
Identification of bryozoans to genus or species level is not easy: over 15,000 species have been recorded in the geological record! The best clues to identification are usually given by the structure of the colony (the zooarium, as it is known) - e.g. the way in which it branches or is packed together, and the detailed structure of the individual fronds of which it is composed. For definitive interpretation, however, much more detailed microscopic analysis is required of the surface and internal structure of the hard parts that once encased the individual (the zooecia). These are usually made of calcite, and vary in shape according to the species, and the growth stage. Important features include the form of the internal chambers and of the opening out of which new zooids emerge, the presence and shape of spines on their surface, and the presence and shape of a lid over the aperture. Some images showing the different forms that fossil bryozoa may take is provided to the right. A useful source, providing descriptions and good photographs of Bryozoa, is Bryozoa.net The British Natural History Museum also has a growing catalogue of images for different fossil species from across the world. Further Reading: Smith, A.M. 1995 Palaeoenvironmental interpretation using bryozoans: a review. Marine Palaeoenvironmental Analysis from Fossils 83, 231-243. Taylor, P.D. 2005 Bryozoans and palaeoenvironmental interpretation. Journal of the Palantaeological Society of India. 50(2), 1-11 |
Images of live Bryozoa, drawn by the zoologist Ernst Haeckel
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