Phylogeography and gut content of Priapulus caudatus in Norway

Abstract

Priapulus caudatus is a marine worm in the phylum Priapulida, commonly known as penis worms. Since it was discovered, P. caudatus has had many names that are now considered synonyms. Fossils of Priapulida from the Cambrian period are found all over the world, and extant species show that there have been little changes in their morphology since the Palaeozoic. P. caudatus are found in clay/muddy sediment from shallow waters to great depths and records are mostly confined to the northern hemisphere. There is not much knowledge about the role of priapulids in the marine ecosystem, but locally they can be abundant members of benthic communities. Few studies about their diet are available from e.g., the Baltic Sea and Canada, which indicates that extant priapulids feed on a variety of invertebrates like polychaetes, Ophiurida and Amphipoda, but also detritus and meiofauna. Likewise, the priapulid Ottoia prolifica, a very abundant species from the middle Cambrian Burgess Shale biota, is found to have a diet consisting of both live prey such as various invertebrates, and detritus present in its habitat. For determining the diet of P. caudatus in Norwegian waters, X-ray microtomography was used considering its capability of providing more details than when utilizing traditional microscopy methods. It is a non-destructive way of investigating specimens, with the possibility of also investigating the gut contents of fossil priapulids. Detritus and sediment were found to be the main gut content, with some foraminifers, suggesting it being a detritivorous animal that occasionally feed on other invertebrates. Additionally, DNA was extracted from the gut of specimens from the study site in Tromsdalen to be further analyzed with DNA metabarcoding. Metabarcoding did not work, but COI sequences revealed interesting phylogeographic relationships with potentially cryptic species.