The bryozoans are divided into three very distinct monophyletic classes (Fuchs et al. 2009). Members of the class Phylactolaemata are entirely freshwater species; the Stenolaemata are exclusively marine, and Gymnolaemata, the largest class, containing 75% of living bryozoan species, is primarily marine, although some species inhabit brackish water (Brusca and Brusca 2003; Kozloff 1990).