Patella (gastropod)

Patella Temporal range: Eocene–Recent PreꞒ Ꞓ O S D C P T J K Pg N
A group of live Patella vulgata on a rock in Wales
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Subclass:	Patellogastropoda
Family:	Patellidae
Genus:	Patella Linnaeus, 1758
Type species
Patella vulgata Linnaeus, 1758
Synonyms
Ansates G.B. Sowerby II, 1839 Costatopatella Pallary, 1913 Helcion (Ansates) Sowerby II, 1839 Patella (Patella) Linnaeus, 1758 Patellastra Monterosato, 1884 Patellus Montfort, 1810 (Invalid: unjustified emendation of Patella) Patina Gray, 1847

Patella is a genus of herbivorous marine sea snails, commonly known as limpets, in the family Patellidae within the class Gastropoda. Primarily a marine group of prosobranch gastropods, they typically live on tidal shores in non-tropical climates. As limpets in the family Patellidae, they are a sister group to the other three accepted genera: Cymbula, Helcion, and Scutellastra. Members of the genus Patella are characterized by a cup-shaped shell and gills, and move by means of muscular waves along the foot.

Patella species are found in north-eastern Atlantic and Mediterranean tidal zones. Surveys conducted over the habitat distributions of the four generas show that Patella is generally the northernmost genus, the other three distributed along southeastern Africa towards Asia.

Taxonomy and morphology

The Patella genus includes the species Patella vulgata, Patella aspera, and Patella caerulea, among others, and is a member of the family Patellidae (common name: common limpet).

Shells

Patella shells are single-valved shells with radial sculpture and are made of calcium carbonate. Their shells are typically depressed, conical, and non-coiled, protecting them from heavy wave action through their stable structural shape. As a limpet, Patella has a ventral muscular foot, providing adhesive force to substrates such as rocks through suction and the secretion of mucus. The foot is composed of dorso-ventral and transverse muscles. Longitudinal muscles are absent. Locomotion relies forward-motion retrograde waves, during which sections of the foot lift approximately 0.2 mm from the substrate. Patella typically moves in a forward direction via a ditaxic pedal wave. Backward motion is rare.

Radula

The radula of Patella consists of iron and silica. During radular development, the protein matrix of the bases and cusps, which are rich in tyrosine and tryptophan complexes with chitin, undergoes mineralization to incorporate iron and silica. The radula of common limpets has opaque teeth and can be detected by transmitted light. The median teeth are surrounded by laterals and uncini.

Eyes and other sensory organs

The eyes of Patella form a simple cup lined with pigmented cells. These structures receive lateral rays of light to detect shifts between dark and light fields but cannot construct true images. This minimal sensory architecture matches that of certain clams, corresponding with their sedentary lifestyle on rocky substrates.

Patella also have balancing organs called statocysts. Statocysts consist of statoliths floating against the wall of statocysts and function as sensory organs. Hairs and cilia detect and transfer the statolith signal to pedal ganglia or the pleuro-pedal connectives which are controlled by cerebral ganglia.

Another chemo-sensory organ, the osphradium comes in pairs as large structures in the pallial cavity. The osphradium functions to detect water quality and mating opportunities. It also can prevent predators like sea stars and netted dog whelk from hunting them.

Habitat, niche and life cycle

The preferred niche of Patella is coasts, embayments or estuaries with salinity between 30-40 psu, and their preferred substratum habitats are bedrock, cobbles and crevices. Their niche tends to withstand changing levels in suspended sediment, water flow rates, temperature, turbidity, and wave exposure.

Patella vulgata has been documented to live in salinities lower than 20 psu (practical salinity units) and with low seaweed abundance. In their habitat, they can bear strong tides, changing water levels, with preference to different levels of eulittoral zones. The climates of their habitats vary from seasonally variable sunshine to cold Arctic-like temperatures as the species' range expands.

Patella have a larval stage after spawning between October and January through external fertilization. The larvae are planktotrophic and green in coloration due to the pigment chromoprotein Y. These pelagic larvae can swim for 2–10 days and travel distances greater than 10 kilometers to find rocks to settle on and form shells.

Reproduction and development

Diet

Like the majority of limpets, Patella spp. are herbivores, and primarily eat thin films of algae on the substrates they attach to. Thus, their diet is mainly composed of algae and other cyanobacteria. They use their radula, an anatomical feature that is unique to mollusks, to rasp and grind up food. Although this feature is a synapomorphy of the Phylum Mollusca, it is absent in bivalves.

Patella spp. feeding behaviors are dependent on circatidal and circadian rhythms, often seeing higher feeding activity with the correct season and tidal cycle. P. caerulea shows significant activity during the night time and under submergence, following a 12 hour circatidal clock for its feeding behavior. Patella spp. also exhibit feeding manoeuvres, such as P. vulgata presenting looped movements around their attachment site, often relying on decision making to efficiently use its energy.

Environmental impact

Patella spp. are herbivorous, which makes them particularly well suited for monitoring algal coverage. The environmental effects associated with limpet grazing on Fucale and green algae are numerous. The barnacle species, Semibalanus balanoides, benefits from the grazing behavior of Patella. S. balanoides competes with algae for substrate. Patella feeds on both fucoid and green algae, thus removing them from their substrate, allowing S. balanoides area for substrate attachment. Thus, Patella grazing regulates algal growth, while enhancing S. balanoides settlement, outlining Patella's role as a keystone species as well.

While grazing for algae and other cyanobacteria, their sharp radula scrapes away at limestone too. Therefore, Patella also contribute greatly to the erosion and breakdown of limestone coasts.

Conservation

Members of the genus Patella are important components of rocky intertidal ecosystems, where they help maintain ecological balance through their grazing activity and interactions with other organisms. They are also subject to high levels of environmental stress, making them useful indicator organisms for assessing the health of coastal habitats. As a result, many tidal ecosystems supporting Patella populations are included within Marine Protected Areas (MPAs), both to reduce impacts from overharvesting and to support monitoring of coastal biodiversity.

The genus is particularly sensitive to marine pollution and has been widely used in marine biodiversity and environmental monitoring research. Species such as Patella caerulea are employed in bioindicator studies to assess ocean acidification and to evaluate the impacts of climate change on marine ecosystems.

Human activity and distribution of Mediterranean marine species can be the cause of the problems with the conservation of Patella. Additionally, the genetic variability detected by polymorphic microsatellite markers in Patella populations has only 0.41% variability between populations without isolation of the species. The difficulty of gene flow between species is due to both biotic and abiotic factors.

Conservation of Patella ferruginea has involved the establishment of MPAs to safeguard adult populations. These protected areas help maintain viable breeding populations and can enhance larval dispersal, thereby promoting an increase in gene flow among populations. Increased gene flow is considered beneficial for the long-term conservation of the species by improving genetic diversity and population resilience.

Another solution is to use artificial portable plates (APPs) on the rocks of Western Mediterranean Sea to retain more Patella, because moving to new environment can cause death of limpets and using APPs could reduce mortality and conserve the population by preventing detachment and translocation.

Species

Species within the genus Patella include:

• † Patella alessiae Forli, Dell'Angelo, Montagna & Taviani, 2004
• † Patella alternicostata Sandberger, 1859
• † Patella ambroggii Lecointre, 1952
• †Patella amuritica Wilckens, 1922
• Patella argentaurum Lesson, 1831
• Patella aspera Röding, 1798
• Patella caerulea Linnaeus, 1758
• Patella candei d'Orbigny, 1839
• Patella crocata R.P. Lesson, 1831
• Patella cyanea R.P. Lesson, 1831
• Patella depressa Pennant, 1777 - Patella depressa is a nomen dubium according to Christiaens (1973, 1983); Patella intermedia gets priority. Nevertheless the name Patella depressa is in usage among British authors (e.g. Graham, 1988) and is assumed as valid.
• Patella depsta Reeve, 1855: (taxon inquirendum)
• † Patella estotiensis Lozouet, 1999
• Patella ferruginea Gmelin, 1791
• Patella gomesii Drouet, 1858
• † Patella hebertiana (d'Orbigny, 1850)
• Patella lugubris Gmelin, 1791
• † Patella mahamensis Martín-González, 2018
• † Patella matheyi De Loriol in De Loriol & Koby, 1890
• † Patella maxoratensis Martín-González & Vera-Peláez, 2018
• † Patella nelsonensis Trechmann, 1918
• Patella ordinaria Mabille, 1888
• Patella pellucida Linnaeus, 1758
• Patella piperata Gould, 1846
• † Patella protea Doderlein, 1862
• Patella rangiana Rochebrune, 1882
• Patella rustica Linnaeus, 1758
• Patella skelettensis Massier, 2009
• † Patella staceata Gründel, Hostettler & Menkveld-Gfeller, 2020
• Patella swakopmundensis Massier, 2009
• Patella tenuis Gmelin, 1791
• † Patella tintina Martín-González & Vera-Peláez, 2018
• Patella ulyssiponensis Gmelin, 1791 - synonyms: Patella aspera Lamarck, 1819; Patella athletica Bean, 1844
• Patella variabilis Krauss, 1848
• Patella vulgata Linnaeus, 1758

Species brought into synonymy

See also

• Limpet

References

This article incorporates CC-BY-3.0 text from the reference.

External links

• Linnaeus, C. (1758). Systema Naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Editio decima, reformata [10th revised edition], vol. 1: 824 pp. Laurentius Salvius: Holmiae
• Sowerby, G. B., II (1839). A Conchological Manual. G. B. Sowerby, London, v, 130 pp., 24 pls
• Pallary, P. (1912). Catalogue des mollusques du littoral méditerranéen de l'Egypte. Mémoires de l'Institut d'Egypte. 7(3): 69-207, pls 15-18.
• Monterosato, T. A. di. (1884). Nomenclatura generica e specifica di alcune conchiglie mediterranee. Virzi, printed for the Author, Palermo, 152 pp.
• Christiaens J. (1973). Révision du genre Patella. Bulletin du Muséum National d'Histoire Naturelle de Paris (3)Zoologie 121: 1305-1392
• Powell, A. W. B. (1973). The patellid limpets of the world (Patellidae). Indo-Pacific Mollusca. 3(15): 75-206

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