Fossil Record

- Due to their soft body, they have an extremely sparse fossil record.

- Lecathylus gregarious is a peanut worm fossil from the early Silurian period

- A group of fossils known as hyoliths have been found in rocks through the Paleozoic period. These organisms had conical shells with an operculum linking them to molluscans. However, a few fossils of Hyoliths have been found to show traces of a looped and coiled intestine comparable to living sipunculans. Furthermore sipunculans secrete a calcified anal plate, so it is not hard to think that past relatives may have secreted more extensive shells.