Bryozoa are small, colonial animals, also known as moss-animals or sea-mats. The majority of this group live in the sea and generally build a rigid skeleton out of calcium carbonate. The oldest fossil bryozoans are known from the early Ordovician Period.
The volume on bryozoans was one of the first parts of The Treatise on Invertebrate Paleontology to be published. The 1953 volume, written by the American palaeontologist Ray Bassler, was just over 250 pages long and described and illustrated all the then known fossil bryozoan genera. Less than twenty tears later it was realised that a second edition would be needed because of the significant advances in knowledge that had been made. The first of the revised editions was published in 1983; this volume, over twice the size of the first, had a detailed introduction to the group and described the genera of two bryozoan orders. The second of the revised editions is currently in preparation. It will also include two orders: the fenestrates, being described by Dr Ken McKinney (Appalachian State University) and Dr Patrick Wyse Jackson (Trinity College, Dublin) and the trepostomes by Dr Richard Boardman (Emeritus Curator, National Museum of Natural History, Smithsonian Institution) and C.J. Buttler.