Evolution of phylactolaemate bryozoans


Julian Bibermair

PhD Student (Adv. Thomas Schwaha)

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


Among Lophotrochozoa bryozoans represent a phylum of predominantly marine suspension feeders with a colonial lifestyle. Most of the 6000 extant species belong to the Myolaemata (Stenolaemata, Gymnolaemata), whereas approx. 90 species belong to the Phylactolaemata, which is the sister taxon of Myolaemata and therefore crucial for ground pattern reconstruction of the phylum. Like in all bryozoans, a single zooid of the exclusively freshwater inhabiting phylactolaemates consists of a soft body (polypide) that can be retracted into the protective body wall (cystid). Recent studies on both, myo- and phylactolaemates show that soft body morphology yields numerous characters useful for ground pattern reconstruction. Despite numerous studies focussing on the morphology of phylactolaemates, there are still several gaps missing in order to gain a more complete picture of the diversity of morphology characters among the clade. Consequently, the aim of this study is to fill these gaps by analysing the morphology of phylactolaemates in order to reconstruct an ancestral character state and their evolution. Selected species are investigated via methods such as confocal microscopy of immunocytochemical labelled specimens as well as serial section-based 3D-reconstructions. First modern data on lophopodids, which to date remain almost uninvestigated, will be exemplary presented. The particular example will show novel data on the neuromuscular system of Asajirella gelatinosa, but also additional characters possibly apomorphic of the family. The data on the nervous system of A.gelatinosa confirm the general bauplan of phylactolaemate neuroanatomy, whereas myoanatomical details show higher variability among the families. Characters such as the cerebral ganglion and the epistome (a phylactolaemate-specific organ) show characteristics probably apomorphic to the Lophopodidae.