The Patellogastropoda, common name true limpets and historically called the Docoglossa, are members of a major phylogenetic group of marine gastropods, treated by experts either as a clade or as a taxonomic order.
The clade Patellogastropoda is deemed monophyletic based on phylogenetic analysis.
Patella ferruginea, commonly known as the ferruginous limpet (sometimes, as the ribbed Mediterranean limpet) is a species of true limpet, a marine gastropod mollusk in the family Patellidae. It is a large limpet, endemic to the western Mediterranean Sea, and although common in the past, it is now rare and restricted to only a few locations.
Limpets are a group of aquatic snails with a conical shell shape (patelliform) and a strong, muscular foot. This general category of conical shell is known as "patelliform" (dish-shaped). Existing within the class Gastropoda, limpets are a polyphyletic group (its members descending from different immediate ancestors).
All species of Patellogastropoda are limpets, with the Patellidae family in particular often referred to as "true limpets". Examples of other clades commonly referred to as limpets include the Vetigastropoda family Fissurellidae ("keyhole limpet"), which use a siphon to pump water over their gills, and the Siphonariidae ("false limpets"), which have a pneumostome for breathing air like the majority of terrestrial Gastropoda.
Fissurellidae, common name the keyhole limpets and 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.