The earliest bryozoan parasite: Middle Ordovician (Darriwilian) of Osmussaar Island, Estonia

The earliest known macroscopic endobiotic symbionts are described from Middle Ordovician bryozoans of Osmussaar Island, Estonia. The bryozoan symbionts represent a new ichnospecies and ichnogenus, Anoigmaichnus odinsholmensis ichnosp. nov., which occurs only in Mesotrypa bystrowi. It most likely represents a parasite. The shape of the trace is consistent with a worm-like animal, making the annelids likely candidates for the trace maker. The increase in predation pressure may have been among the direct causes leading to the appearance of various macroscopic endobiotic symbionts in the Ordovician.