One could easily miss the bryozoans (entoprocts) or mistake them as an alga or coral. Bryozoans are a phylum of microscopic, aquatic invertebrates that live in sessile colonies of genetically identical members. The individuals are not autonomous and are termed zooids. They grow as calcified or gelatinous encrusting masses or branching tree-like structures. Having said that, there are notable exceptions, including a genus of solitary species (Monobryozoon), a mobile species (Cristatella mucedo), and a recently found planktonic species (in genus Alcyonidium) that floats as a ball (Peck et al. 1995). Like the phoronids and the brachiopods they feed using a specialized horseshoe-shaped structure called a lophophore. Known also as “moss animals,” there are somewhere between 4000-6000 living species, some estimate that number closer to 8000 species (Ryland 2005). Most bryozans are marine or brackish, fewer than 100 species live in freshwater (Massard and Geimer 2007). About 15,000 fossil species have been found, dating from the early Ordovician/late Cambrian. Molecular phylogenetic analyses indicate that bryozoans originated earlier in the Cambrian period (along with almost all other invertebrate phyla) and that the earliest bryozoans were non-calcified, thus did not fossilize (Fuchs et al. 2009).
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