Mildred J. Johnson


Recent developments on the endolithic bryozoan genus Immergentia and the description of a new species

PhD Student
Advisor: Thomas Schwaha

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


Endolithic bryozoans can be distinguished by borehole etchings unique to a specific genus. In immergentiids, boreholes are typically spindle-shaped, and zooids are positioned almost vertically in the substrate. Building on Silén’s knowledge of the soft body morphology of these animals in 1947, additional/recent serial histological sections and modern 3D reconstructions have revealed the presence of a cardiac constrictor and true stolons not previously reported for Immergentiidae. In addition, DNA extraction and morphological characterization have confirmed the discovery of a novel intertidal species, Immergentia stephanieae sp. nov., from Roscoff, France. Bioerosion rates are well documented in other boring taxa, but are lacking for boring bryozoans. To bridge this knowledge gap, laboratory experiments were conducted on the novel species and Immergentia cf. suecica. The bryozoans were fed a culture mixture consisting of the microalgae Tisochrysis lutea and diatom Chaetoceros calcitrans, and growth in the feeding treatment was compared with the control. Generally, nutrient availability and feeding enhanced growth. The growth rate of small colonies of comparable size was greater in the feeding treatment and relatively lower in the control for both immergentiids. However, in larger colonies of I. stephanieae sp. nov., this trend was not consistent, with growth occasionally being higher in the control than in the feeding treatment. This result can be attributed to the colony’s age, space for expansion, and/or resource reallocation. Furthermore, temporal observations of colonies hint at peak seasonality of immergentiids from Roscoff. Finally, the challenge of measuring the growth of boring bryozoans is highlighted.