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Bryozoans in this family form encrusting colonies. Zooids are rectangular or oval. Gymnocyst present, often very extensive. Cryptocyst always present, reduced in some genera but extensive in others. Frontal membrane visible in most species, occasionally partly obscured by overarching spines. Prominent hyperstomial ovicells present, often ornamented with knobs (umbones), ridges or avicularia. Avicularia occur in many genera, often of more than one type and sometimes of unusual form. Dietellae often present showing most clearly at the edge of the colony.
(Hayward and Ryland, 1998)