Fissurellidae, common name the keyhole limpets and slit limpets, is a taxonomic family of limpet-like sea snails, marine gastropod molluscs in the clade Vetigastropoda.

Their common name derives from the small hole in the apex of their cone-like shells. Although superficially resembling "true" limpets, they are in fact not closely related to them.

Fissurelloidea. Retrieved May, 08 2021, from en.wikipedia.org/wiki/Fissurellidae.

Diodora aspera, also known as the rough keyhole limpet, is a species of sea snail, a marine gastropod mollusk in the family Fissurellidae, the keyhole limpets. Although similar in appearance to a common limpet, it has a hole near the apex of its shell, and is only distantly related. It often has a scaled polychaete worm Arctonoe vittata living inside its shell as a commensal. In the event that it is attacked by a starfish, it extends flaps of mantle to defend itself, and the worm also helps drive the predator away.

Diodora aspera. Retrieved May, 08 2021, from en.wikipedia.org/wiki/Diodora_aspera.