ABSTRACT
Most cheilostome bryozoans possess prominent brood chambers called hyperstomial ovicells. Each ovicell comprises a hemispherical double-walled fold (ooecium), surrounding the brooding cavity and originating from either the maternal (egg-producing) or its distal daughter zooid. The internal wall is called the entooecium, the external wall the ectooecium, and there is an ooecial lumen between them that is connected with the perigastric coelom of the ovicellproducing zooid through one or more communication pores. The ovicell opening is closed either by the operculum of the zooidal aperture, or by an evagination of the maternal cystid wall called an ooecial (inner) vesicle or ooecial plug (see Ostrovsky 1998, 2002, Taylor & McKinney 2002, Ostrovsky & Schäfer 2003 for further details and discussion).
