Oriostoma was a snail that fed by scraping up algae from corals and other surfaces in the Gotland reefs. The shell was almost discus-shaped, with a deep hollow on the underside.
This type of gastropod shell is unusual in the sea today, since such shells are vulnerable to predators. But since there were not very many predators capable of breaking up shells of snails in Silurian times, Oriostoma coped well.