This bryozoan frequently grows as thin, flat white crusts on large kelp. The zooids are small rectangular boxlike structures. Most of the frontal of the zooid is membranous instead of calcified, and they have an operculum. They have no distinct spines, though there are knoblike or small spinelike protuberances on the margins between zooids (photo) (and see the note below). They have no avicularia or vibracula. The side walls between zooids are thin and not heavily calcified (photo), though they may be slightly serrated. Colonies are often nearly circular and usually nearly white. The individual zooids are little calcified and almost clear.