Individuals from three populations ofPectinatella magnificafrom different habitats in Ohio (U.S.A.) were analyzed for a variety of ecological and morphological parameters. Genic variation was analyzed using starch gel electrophoresis. Individuals from a lake and an estuary population showed no difference in length, width or stick attachment diameter. Individuals from stream habitat were significantly narrower than individuals of the same length from either the lake or estuary. Two (peptidase-2 and esterase-1) of seventeen presumptive genetic loci were polymorphic. Percent polymorphism (5.9%) and mean heterozygosity (0.013) were lower than values published for other bryozoans and invertebrates as a whole.