Evolution of the Priapulida

Small group of animals, great diversity

The Priapulida are a group of animals with only 22 known species. Despite this small number of species, they are very heterogeneous. Some of the species are macroscopic, i.e. centimetre-sized (between a few and 40 cm), while others are microscopically small (a few mm long). This mainly affects their reproductive biology: the large species release their gametes into the water and fertilisation takes place there, while the small species fertilise internally. There are still large gaps in our knowledge of the morphology of priapulids. On the one hand, not all developmental stages (there are hatchling larvae, lorica larvae, postlarval and adult stages) are always known, and on the other hand, their fine structure is often insufficiently described. As the characteristics vary considerably, this results in problems with the homologisation of individual structures.

What is the original body size?

Our aim was to describe some species in detail and to formulate homology hypotheses for individual structures. In addition, we were investigating the relationships of priapulids using transcriptome data and, in collaboration with a research group at Harvard University, using UCEs (ultraconserved elements). An important goal was to find out the original body size of priapulids in order to see whether a large or a small body size has newly evolved within the priapulids. From this it can be deduced what consequences either an enlargement or a miniaturisation has for the body organisation.