SUMMARYThe diatomCocconeis scutellum(Meunier) colonizes the surface of young plants emerging from the mud in the spring and the usually emersed plant tips as they are knocked over and become immersed in the fall to form a virtually unialgal mat. Broken frustules and detritus adhere to form a crust which then becomes colonized nonselectively by a variety of microorganisms. Removal of the crust shows that the original “cobblestone” surface of the eelgrass is obscured with a layer of deformed cells ofC. scutellumwhich appears to be impressed into the epithel