COMPARATIVE-STUDIES OF OVICELL ANATOMY AND REPRODUCTIVE PATTERNS IN CRIBRILINA-ANNULATA AND CELLEPORELLA-HYALINA (BRYOZOA, CHEILOSTOMATIDA)

Investigations of the common boreal-arctic cheilostomate bryozoans Cri brilina annulata and Celleporella hyalina have shown that the two spec ies possess similar ovicell structures and reproductive patterns. Both species are characterized by frontal dwarf ovicellate zooids, that ar e female autozooidal polymorphs in C, hyalina and simultaneous hermaph roditic autozooids in C. annulata. The latter species in addition has ovicellate autozooids of the usual type. Each ovicell is formed from a maternal zooid only, and its cavity is lined by the outer hemispheric al fold (ooecium) and the distal zooidal wall. The coelomic cavity of the ooecium is separated from the body cavity of the maternal zooid by a transverse wall with simple pores. Each pore is closed by a cell pl ug, and the ooecia may be considered as kenozooids. Each oocyte is acc ompanied by a single nurse cell that degenerates after ovulation. The eggs are macrolecithal in C. annulata and microlecithal in C. hyalina, and the former species is a non-placental brooder whereas the latter forms a placenta. Fertilization is precocious. Possible mechanisms of sperm entry as well as oviposition are discussed. The literature conce rning ovicell structure and development in cheilostomates is analysed. It is proposed that the brood chamber of cribrimorphs evolved by a fu sion of costae and a reduction of the daughter zooid in ancestral form s. (C) 1998 The Royal Swedish Academy of Sciences. Published by Elsevi er Science Ltd. All rights reserved.