Description

 

"True" limpets are found in this superfamily, which includes several very similar families, among which the shells are all solid. Their  volcano-shaped cousins are the keyhole limpets, which differ in having a slit or top opening for the waste stream (see Fissurellidae). But in the true limpets,  both nutrient and waste streams enter just under the shell, through two, separate grooves in the mantle. This feature is common to many primitive gastropods comprising the Patellogastropoda and Vetigastropoda clades. 

Limpets, generally, do not have eyes and seem to be guided mainly by chemoreception based on mucus deposits. Most are shallow water molluscs, but those in the Lepetidae family are a subtidal species. In the Acmaeidae family, smaller species tend to seek out tide pools and other quiet locations. The smallest of the Acmaidae may attach to fronds of vegetation. All of the true limpets are vegetarians. The Acmaeidae do not use suction to attach; rather, they find imperfections in the surface to use for attachement. Like the Patellidae, they are also mobile.

The more flattened conical shells of the Patellidae are ideally shaped to protect them against being crushed by waves that pound against the exposed rocky surfaces they cling to, and their large flat foot acts somewhat like a suction cup to attach them. None are stationary. They move about while grazing on vegetation and detritus, some making prolonged trips away from their home base while the tide is in. Of considerable interest is that on returning at dawn, they move about to reorient their body for a precise fit into the scar they had excavated into the rock surface --even if the rock is picked up and moved or re-oriented. 

In the deep water limpets, the radula is especially well designed for boring into rock. Recurved teeth are hardened with iron and silicon oxides at the tips.

Currently, Collisella, Tectura, Notoacmaea and most species formerly of the genus, Acmaea, are reclassified to the genus, Lottia (Carlton, 2007) . The several current families listed below are defined by significant differences in soft tissue anatomy, established by scanning electron micrography. Differences also include chromosome number, and shell microstrucure Beechey, 2008; Sasaki, 1998).

Classification

Class: Gastropoda

Clade: Patellogastropoda

Superfamily: Patelloidea

Families & Major Genera 

Acmaeidae (tide pools)

Genus: Acmaea

Lottiidae (shallow water)

Genus: Lottia [Collisella, Tectura, Notoacmaea]

Patellidae (shallow water)

Genus: Patella

Nacellidae (shallow water)

Genus: Cellana

Genus: Nacella

Lepetidae (deep water)

Genus: Iothia

Genus: Lepeta

Genus: Neomphalus

Genus: Propilidium

Notoacmaea scutum (Rathke, 1833)
Plate Limpet
4.5 cm

Lottia insessa (Hinds, 1842)
Seaweed Limpet
1.1 cm-2.0 cm

Patella granatina (Linnaeus, 1758)
Sandpaper Limpet
6.1 cm

Patella oculus (Born, 1778)
South African Eye Limpet
W. Cape, S. Africa; 7.7 cm