Fissurellidae,

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...

the keyhole limpets and slit limpets, is a

taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

limpet Limpets are a group of aquatic snails that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" descended indep ...

-like

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

s in the clade

Vetigastropoda Vetigastropoda is a major Taxonomy (biology), taxonomic group of sea snails, marine (ocean), marine gastropod mollusc, mollusks that form a very ancient lineage (evolution), lineage. Taxonomically the Vetigastropoda are sometimes treated as an O ...

.Rosenberg, G. (2012). Fissurellidae. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=111 on 2013-01-02 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.

Distribution

The distribution of fissurellids is worldwide, from cold waters to tropical waters. Powell A. W. B., ''New Zealand Mollusca'', William Collins Publishers Ltd, Auckland, New Zealand 1979

Habitat

Fissurellids live in habitats on and under rocks in the lower

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

s to deeper waters.

Shell description

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 A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

Patellogastropoda The Patellogastropoda, common name true limpet Limpets are a group of aquatic snails that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning th ...

. This conical shape of the shell allows keyhole limpets to withstand wave attack on exposed rocks. The shell has a reticulate (= net-like) sculpture with strong radial ribs and lacks an operculum. The shell ranges from 3 mm to 13.2 cm. The great keyhole limpet ''(

Megathura crenulata ''Megathura crenulata'' is a northeastern Pacific Ocean species of limpet in the family FissurellidaeRosenberg, G. (2015)''Megathura crenulata'' (Sowerby I, 1825).''In'': MolluscaBase (2015). Accessed through: World Register of Marine Species on ...

'') measures up to 13.2 cm. For respiration, the shells of fissurellids have a single

apical Apical means "pertaining to an apex". It may refer to: *Apical ancestor, refers to the last common ancestor of an entire group, such as a species (biology) or a clan (anthropology) *Apical (anatomy), an anatomical term of location for features loc ...

or subapical perforation ("keyhole"). This opening at the top allows a direct exit of exhalant water currents together with waste products from the mantle cavity. The water enters under the edge of the shell near the head and passes over large paired gills. Most young species in this family have a marginal slit in the middle of the anterior end of the spiral shell. Some species possess just a short internal groove at the anterior end. The paired organs in the mantle cavity represent a primitive condition in gastropods. The soft body consists of a well-developed head, a short muzzle. It has a broad and flat foot and a well-developed mantle. This foot exerts a strong suction, adhering the keyhole limpet to its hard substratum. The mantle extends in some species partly or completely (as in ''Megathura crenulata'') over the shell. The tentacles at the ''epipodium'' (the lateral grooves between foot and mantle) are well developed. The species in ''

Medusafissurella ''Medusafissurella'' is a genus of minute deepwater keyhole limpets, marine gastropod mollusks or micromollusks in the family Fissurellidae, the keyhole limpets and slit limpets.Bouchet, P.; Gofas, S. (2012). Medusafissurella McLean & Kilburn ...

'' have numerous

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