Phylactolaemata

Phylactolaemata, the freshwater bryozoans, is one of the three classes of the phylum Bryozoa.  Representing a small percentage of the bryozoan diversity, this group is made up of 74 described species, 59 of which belong to a single family (Plumatellidae).  All Phylactolaemata species live only in fresh water, in sessile colonies of genetically identical individuals called zooids.  Although bryozoans in other classes have colonies comprised of different types of zooids, all Phylactolaemata species have only the feeding autozooids, characterized by an un-mineralized, gelatinous or protinaceous exoskeleton  (Hartikainen et al. 2013).  Colonies, which can be encrusting or branched, usually attach to surfaces in still or running waters.  While they reproduce sexually, genetic individuals can persist in non-ideal environmental conditions such as freezing or desiccation by producing large numbers of dormant “statoblasts,” masses of cells generated asexually and protected with chitinous shells.  Statoblasts, which look like little seeds, can disperse long distances and develop into a colony-forming zooid in more favorable conditions (Ruppert et al. 2004; Wikipedia 2013).  Colonies of many freshwater bryozoan species grow rapidly, and often found in large abundance.  Species of phylactolaemata have been studied for their role in nutrient cycling, as agents causing biofouling problems, as creators of habitats for other species, and as hosts for a parasite destructive to salmonid fish affecting both farmed and wild salmon populations (Hartikainen et al. 2013 and references therein).