Diodora graeca is a sea snail

Snail

Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...

 or limpet

Limpet

Limpet is a common name for a number of different kinds of saltwater and freshwater snails ; it is applied to those snails that have a simple shell which is more or less conical in shape, and either is not spirally coiled, or appears not to be coiled in the adult snails.The name limpet is most...

, a marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 gastropod mollusk in the family Fissurellidae, the keyhole limpet

Keyhole limpet

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.Fissurellidae is the only family in the superfamily Fissurelloidea....

s.

It was originally described by Linnaeus in 1758 as Patella graeca (basionym

Basionym

Basionym is a term used in botany, regulated by the International Code of Botanical Nomenclature...

).

Distribution

This keyhole limpet can be found beneath stones and clinging to rocks in the sublittoral zone

Littoral

The littoral zone is that part of a sea, lake or river that is close to the shore. In coastal environments the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged. It always includes this intertidal zone and is often used to...

 (up to a depth of a few hundred meters) in the Mediterranean  and West Africa to the North Sea (widespread on the coasts of Ireland and western Britain) and the subarctic North Atlantic. The specimens washed up on the beaches of the North Sea are almost certainly fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 (from the Pliocene

Pliocene

The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...

 and the Eemian), as this species no longer occurs in the south-eastern part of the North Sea.

Description

The oval shell is small (25 mm long and 18 mm wide) and rather flat. It has no whorls

Whorl (mollusc)

A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...

 and is shield-shaped. The base of the shell is somewhat bent. Its aperture

Aperture (mollusc)

The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....

 is situated at the dorsum and is keyhole-shaped. This hole serves as an outlet for water and waste products. The shell has a slight reticulated sculpture with concentric cords crossed by radial ridges and with the alternate ridges larger. The color of the shell varies from creamy white to yellow white and is often slightly orange tinted.

This species is mainly herbivorous and also feeds on detritus

Detritus

Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...

. The animal has a broad creeping foot and a developed mantle. Its carotenoid content has been investigated and the following substances have been found : α-, β, γ-carotene

Carotene

The term carotene is used for several related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but cannot be made by animals. Carotene is an orange photosynthetic pigment important for photosynthesis. Carotenes are all coloured to the human eye...

, zeaxanthin

Zeaxanthin

Zeaxanthin is one of the most common carotenoid alcohols found in nature. It is important in the xanthophyll cycle. Synthesized in plants & some micro-organisms, it is the pigment that gives paprika , corn, saffron, and many other plants & microbes their characteristic color.The name is derived...

, diatoxanthin, mutatoxanthin and astaxanthin

Astaxanthin

Astaxanthin is a carotenoid. It belongs to a larger class of phytochemicals known as terpenes. It is classified as a xanthophyll, which means "yellow leaves". Like many carotenoids, it is a colorful, lipid-soluble pigment. Astaxanthin is found in microalgae, yeast, salmon, trout, krill, shrimp,...

.

Synonyms

• Fissurella mamillata Risso, 1826
• Fissurella reticulata (Da Costa, 1778)
• Patella apertura Montagu, 1803
• Patella graeca Linnaeus, 1758

Sources

• Oliver APH, The Hamlyn Guide tio Shells of the World, Hamlyn Publishing Group, 1975, ISBN 0-600-56577-7
• Rolán, E., 2005. Malacological Fauna From The Cape Verde Archipelago. Part 1, Polyplacophora and Gastropoda.
• Muller, Y. (2004). Faune et flore du littoral du Nord, du Pas-de-Calais et de la Belgique: inventaire. [Coastal fauna and flora of the Nord, Pas-de-Calais and Belgium: inventory]. Commission Régionale de Biologie Région Nord Pas-de-Calais: France. 307 pp.
• Backeljau, T. (1986). Lijst van de recente mariene mollusken van België [List of the recent marine molluscs of Belgium]. Koninklijk Belgisch Instituut voor Natuurwetenschappen: Brussels, Belgium. 106 pp.