Fissurellidae

Fissurellidae, commonly called keyhole limpets or slit limpets, is a taxonomic family of small to medium-sized 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.

The distribution of fissurellids is worldwide, from cold waters to tropical waters.

Fissurellids live in habitats on and under rocks in the lower intertidal zones to deeper waters.

Keyhole limpets somewhat resemble true limpets because of the simple conical shape of their shells, but in reality they are not closely related to true limpets, which are in the clade Patellogastropoda.

This conical shape and the low profile of the shell allow keyhole limpets to withstand wave attack on exposed rocks to which they attach firmly with their strong, muscular foot.

The shell may vary in color and pattern. The shell has a reticulate (= net-like) structure with strong radial ribs and lacks an operculum.

The shell ranges from 3 mm to 13.2 cm. The great keyhole limpet (Megathura crenulata) measures up to 13.2 cm.