Sebastian H. Decker


Life cycle and systematics of the boring bryozoan family Penetratiidae

PhD Student
Advisor: Thomas Schwaha

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


Among the phylum Bryozoa there are endolithic forms which bore into calcified substrates such as the shells of molluscs. Four extant families of endolithic bryozoans are currently recognized and belong to the clade of soft bodied ctenostome bryozoans. One of them are the Penetrantiidae with the sole genus Penetrantia including 12 species. Penetrantiids have characteristic features like an operculum and polymorphic gonozooids for brooding of embryos what separates them from all other boring bryozoans. However, very little is known about their diversity, species identity, life cycle and even the phylogenetic placement is uncertain. Consequently, this study tries to answer these questions by an integrative approach of morphological and molecular methods. Investigations on the muscular system of the operculum and brood chambers suggests convergent evolution of these structures and promotes a ctenostome affiliation. This is supported by a phylogenetic analysis based on 18S and mitochondrial protein coding genes. Additionally, this analysis confirms a new species from Japan and cryptic species from the North Sea, and potentially from New Zealand and Chile. Species identification remains a great challenge especially between closely related species, but this study provides many new characters that will aid in future species identification. There is a big gap in knowledge concerning the life cycle, colony formation and growth rates. Growth experiments yielded new information and provide first growth rates indicating that they bore faster than previously estimated. Although early colony formation seems very conserved among penetrantiids some uncovered specific traits might help in future species identification. However, reproduction in penetrantiids remains largely an open question as free-swimming larvae and their settlement has never been observed yet.