Advisor: Thomas Schwaha

PhD Defensio
Thursday, August 29th 2024, 10:00 am CET
Lecture Hall 2, University Biology Building, University of Vienna
Djerassiplatz 1, 1030 Vienna

Abstract

Among the lophotrochozoan phylum Bryozoa, the extant endolithic families—Terebriporidae, Spathiporidae, Penetrantiidae, and Immergentiidae—are among the least studied ctenostome bryozoans. Endolithic bryozoans immerse their colonies into calcareous substrates by chemical dissolution of calcium carbonate, hence the name 'boring bryozoans'. Due to their cryptic nature, most questions concerning their systematics, species diversity, and life history remain unanswered. Consequently, this thesis aims to improve our knowledge about the biology and systematics of these peculiar bryozoans by studying the families Penetrantiidae and Terebriporidae. Samples from over 25 different locations were studied and included at least seven different penetrantiid species and one terebriporid. In an integrative approach combining various morphological methods and a molecular phylogeny based on 16 genes from nearly 30 different ctenostome species, the ctenostome affinity of Penetrantiidae was confirmed, although they are not closely related to other stolonate ctenostomes as previously suggested. The operculum and brood chamber in Penetrantiidae evolved independently from their cheilostome counterparts, as the associated musculature differs and are considered apomorphic for this family. The opercula in three penetrantiids contain calcium carbonate, which represents the first evidence of biomineralization in ctenostomes. Furthermore, this thesis describes Penetrantia japonica as a new species and uncovered cryptic species complexes in New Zealand and Northern Europe. The analysis also shows a closer relationship between Terebripora ramosa and arachnidioid ctenostomes, as sister to Immergentia. Since the phylogenetic analysis includes representatives of all major ctenostome clades, it sheds new light on general ctenostome bryozoan systematics and supports their paraphyly. Growth experiments of Penetrantia clionoides yielded the first growth data of any endolithic bryozoans, which offers novel insights into astogeny and identified apertural rims as ancestrular features in three penetrantiids. Overall, this study significantly enhances our understanding of the biology and systematics of boring bryozoans, laying an important foundation for future projects.