In the Genesee Group (Upper Devonian) of the Catskill delta of New three adaptive types of suspension feeding epizoa are recognized: (1) Commensal (parasitic?) spionid polychaetes were host-specific, boring the shells of selected living brachiopods. Only large hosts were colonized. Although larvae settling randomly with to host size will be most abundant on large hosts, size-selectivity of fossil epizoa can be demonstrated if occurrence of epizoa as a function of host size is known. The relative scarcity of borings in punctate brachiopods supports the theory that caecal secretions repel borers. Borings were oriented radially, perpendicular to the valve margins of the host for ease in maintaining a feeding position in the hosts currents as the shell grew. Borings avoid intersection with each other and the valve surfaces. (2) Encrusting Bryozoa utilized any available hard substrate, whether dead or alive. (3) The tabulate coral Cladochonus was a faculative epizoan which usually lived on the surface of the sediment.