Origin of the cystid epidermis during the metamorphosis of three species of gymnolaemate bryozoans

Summary

Origin and formation of the body wall epidermis of the ancestrula in three species of gymnolaemate bryozoans were analyzed by scanning and transmission electron microscopy. In the ctenostome Bowerbankia gracilis, the aboral pallial epithelium forms the entire cystid epidermis, whereas in the anascan cheilostome Bugula neritina, the wall and roof regions of the internal sac form the epidermis. In the ascophoran cheilostome Watersipora culcullata, however, both the pallial epithelium and internal sac contribute to the body wall epidermis. In spite of these different origins, the tissues involved in production of the exoskeleton share a common ultrastructure. The various patterns of metamorphosis described here indicate that ancestrular body wall origin may be an important character in the analysis of phylogenetic relationships within the Bryozoa.