The life cycle and systematics of the boring ctenostome bryozoan families Immergentiidae and Spathiporidae


Mildred J. Johnson

PhD Student
Advisor: Thomas Schwaha

Unit for Integrative Zoology, Department of Evolutionary Biology
University of Vienna


An endolithic lifestyle has evolved multiple times in the phylum Bryozoa and at least twice in Recent ctenostomes. Recent species are assigned to four families namely, Immergentidae, Penetrantiidae, Spathiporidae and Terebriporidae. Immergentiids possesses prominent characteristics that set them apart from Spathipora and the other boring ctenostomes.  For example, the autozooids of immergentiids are non-pedunculate and they do not have a gizzard. Furthermore, immergentiids possess analogous stolonate structures called cystid appendages which differ from true stolons, i.e. kenozooidal polymorphs, in other stolonate forms. To date, 17 species are assigned to Immergentia and 14 to Spathipora, comprised of 11 fossil and 7 Recent species, respectively. The majority of species descriptions were based on external characteristics such as zooid shape, aperture shape and colony growth patterns with details of the soft body morphology limited to one representative species from each genus. The last detailed histological examination of I. californica was in 1947 and that of S. mazatlanica in 1975. Therefore, the objective of this study is to gain further insights into various zooidal aspects of these families. To achieve this, we use a combined approach which includes traditional histological sectioning methods and resin casts, examination of zooids after decalcification of shells, as well as visualization with confocal laser scanning microscopy and imaging software. Growth rates for Immergentia are reported for the first time. In addition, preliminary results reveal the presence of a cardiac constrictor in the gut of Immergentia, a characteristic found in other non-boring ctenostome species with cystid appendages and anastomoses. We also report the presence of Spathipora off the coast of Roscoff France, for the first time. To ensure adequate identification of species, we propose that descriptions of colony structure, external characters of autozooids and soft-body morphology be combined.