| Keyhole limpet | |
|---|---|
| A group of shells of Diodora cayenensis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| (unranked): | clade Vetigastropoda |
| Superfamily: | Fissurelloidea Fleming, 1822 |
| Family: | Fissurellidae Fleming, 1822 |
| Genera and species | |
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See text |
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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.[1]
Fissurellidae is the only family in the superfamily Fissurelloidea.
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The distribution of fissurellids is world-wide, from cold waters to tropical waters.[2]
Fissurellids live in habitats on and under rocks in the lower intertidal zones to deeper waters.[2]
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 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) measures up to 13.2 cm.
For respiration, the shells of fissurellids have a single apical 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 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 soft body consists of 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.
In addition to the possession of this hole, slit or groove, keyhole limpets differ in several other ways both internally and externally from true limpets.
Keyhole limpets are in essence herbivorous, feeding primarily on algae, but are also detritus feeders. A few species in the genera Diodora and Emarginella are carnivorous, feeding on sponges. Puncturella has been reported to digest diatoms and detritus. Puncturella aethiopica feeds mainly on Foraminifera.[3]
Family Fissurellidae Fleming, 1822
This classification was based by Bouchet & Rocroi on the studies by Keen (in Moore) (1960), Christiaens (1973) [4] and McMean (1984).[5]
Genera within the family Fissurellidae include[6][7]: