Patella (gastropod)


Patella are a herbivorous genus of sea snails limpets in the family Patellidae, further placed under the class Gastropoda. Primarily a marine based genus of prosobranch gastropods they most commonly live on coastal tidal shores in varying non tropical climates. As limpets under family Patellidae, they share sister taxa with 3 other accepted genus Cymbula, Helcion, and Scutellastra. Patella is characterized by their cup-shaped shell and gills, with their form of movement in waves.
The genus of Patella are geographically found around north eastern Atlantic and Mediterranean tidal beds. Surveys conducted over the 4 genus' habitat distribution show that Patella are generally the northern most genus with the other 3 distributing along south eastern Africa towards Asia. They tend to be subjected to high volumes of environmental stresses and therefore act as key indicator species for the tidal coast health in those regions. As such conservation efforts along coastal regions have marked many tidal ecosystems as Marine Protected Areas, both in efforts of conserving Patella populations from overharvesting and monitoring coastal biodiversity.
Patella are important to keeping ecological balance of its habitats, through managing interactions with other organisms within its environment. The Patella genus is prone to marine pollution and is often used as a key genus upon research for marine biodiversity. Species such as Patella caerulea are used in bioindicator studies to understand ocean acidification and effects of climate change on oceans.

Taxonomy and Morphology

Patella is the genus name of the species Patella vulgata, Patella aspera, and ''Patella caerulea etc, and it belongs to family Patellidae''.

Shells

Patella shells are single-valved shells with radial sculpture and are made of calcium. Their shells are usually reduced conical and non-coiled and can protect them from floods with their stable structure. As a Limpet, Patella has a ventral muscular foot, providing adhesion force to substrates, like rocks, by secreting mucus and using a sucking force. Their foot is made of dorso-ventral and transverse muscles with no longitudinal muscle. Their movement uses retrograde locomotory waves to move forward that foot lifts from the substrate for 0.2 mm. Patella usually moves forward by a ditaxic pedal wave, but rarely moves backwards.

Radula

The radula of Patella consists of iron and silica. The formation of Patella is that, in bases and cusps, proteins tyrosine and tryptophane and chitin becomes amino groups and argentaffin, then they become iron and silica. The radula of common limpets has opaque teeth with surrounded by and, and it can be detected by transmitted lighting.

Gills

As a marine species genus group, Patella breath by using gills. The morphology of their gills are akin to a "double comb" structure, hence the name ctenidia, it functions as the gas exchange organ which uptakes oxygen and discards carbon dioxide. Patella grow secondary gills with the gill filaments located at the pallial groove, unlike the terrestrial snails which have a reduced primary gill and are unable to breathe air through gills.

Eyes and other sensory organs

The eyes of Patella are a simple-cup shape lining with pigmented cells that can detect only dark and bright fields by receiving lateral rays of light connecting with nerve fibres to nerve system but cannot form images. This is the same as some clams due to their sedentary nature and preference of staying on the rock.
Patella also have balancing organs called: statocysts. Statocysts consists 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 ganglion.
Another chemo-sensory organ osphradium come in pairs as large structures in the pallial cavity. Osphradium function to detect water quality and mating opportunities. It also can prevent predators like sea stars and netted dog whelk from hunting them.

Nerve system

The nervous system of marine prosobranch gastropods Patella experience torsion similarly to pulmonate snails. After torsion, the pericarya of nerve cells concentrated at the anterior end forms 2 pairs of cerebral ganglia connected by without myelin sheath. Cerebral ganglia connects to structures such as : tentacles, eyes statocysts, lips, penis, pharynx, salivary glands and stomach. No brain presents in Patella due to the brains of molluscs being highly reduced except for in cephalopods.

Habitat, Niche and Life Cycle

Patella are mainly distributed on the rocky shores at costal regions exposed to waves to in varying degrees. Patella vulgata have been documented to living in salinities lower than 20 psu 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 variant sunshine to cold Arctic like temperatures as the species expands.
The preferred niche of Patella are coasts, embayment or estuaries with salinity between 30-40 psu, and their preferred substratum habitats are Bedrock, Cobbles and Crevices. Their niche tend to bear changing levels in suspended sediment, water flow rates, temperature, turbidity, and wave exposure.
Patella have a larva 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 larvae can swim as the pelagic life forms for 2–10 days and travel greater than 10 km to find rocks to settle on and form shells.

Reproduction and Development

Reproduction

Both hermaphroditism and gonochorism are common in gastropods. The common limpet, Patella vulgata, is a protandrous hermaphrodite, while Patella depressa is gonorchic. Being protandrous, the limpets with larger sizes in P. vulgata are dominated by females, changing from male to female as they grow.
Extant gastropods have lost one of their gonads, with the one that they do possess being situated next to the digestive gland. The gonoduct carries the gametes produced by their one gonad out of the body. In patellogastropods and vetigastropods, the gonoduct is called the urogenital duct as the gonoduct develops alongside the right nephridium in both clades. Thus, this duct functions to transport both gametes and urine. P. vulgata does not possess a penis or uterus, thus it engages in broadcast spawning.

Development

P. vulgata undergoes spiral cleavage and during gastrulation yolk cells occupy the blastocoel. Planktonic trochophore larva that later on develops into a veliger larva is also present within this species of Patellid. P. vulgata also undergoes torsion between its trochophore and veliger larval stages before it takes on a sedentary lifestyle, settling onto a substrate to metamorphose into an adult limpet.

Feeding

Like the majority of limpets, Patella spp. are herbivores, meaning that they 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 one trait absent in bivalves.
Patella spp. feeding behaviors is dependent on circatidal and circadian rhythms, often seeing higher feeding activities 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.

Use as Bioindicators and Environmental Impact

Mollusks are traditionally used as marine bioindicator species, specifically bivalves such as Mytilus spp. Assessing the bioaccumulation within a chosen indicator species is the method that is most frequently utilized when assessing an environment's overall health, especially when Mytilus spp. are used as the bioindicator. However, there are other commonly used approaches to bioindication, such as observing the way in which an organism responds to changes in the environment and how the environmental structure is modified as a result of the introduction of a toxic substance. Because of the many approaches to biomonitoring and the different trophic levels that can be observed, the demand for more species used in official monitoring programs has increased. There are certain characteristics that an organism must possess in order to qualify as an effective bioindicator species. These features include having a wide body of research and knowledge pertaining to the organism, being largely abundant, easy to collect, and mainly sedentary. Patella spp. possess many of these characteristics that make them a suitable alternative bioindicator species.
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

Human activity and distribution of Mediterranean marine species can be the cause of the problem of the conservation of Patella. The problem of Patella population is that the genetics variability detected by polymorphic microsatellite markers, which has only 0.41% variability between populations without isolation of the species. The difficulty of exchanging and communicating between species is due to both biotic and abiotic factors, in which the stochastic factor is messy.
The solution of conserving Patella ferruginea is that establishes marine protected area to protect the adult of Patella, which promote larva to travel further and increase the gene glow. Increasing gene flow of Patella would promote the conservation of the species.
Another solution is to use using artificial portable plates (APPs) on the rocks of Western Mediterranean Sea to retain more Patella because moving to new environment will cause death of limpets and prevent detachment and translocation by using APPs could reduce mortality and conserve the population.

Species

Species within the genus Patella include:

Species brought into synonymy

Patella achates Reeve, 1855: synonym of Acmaea achates Patella aculeata Gmelin, 1791: synonym of Bostrycapulus aculeatus Patella adansonii Dunker, 1853: synonym of Cymbula safiana Patella afra Gmelin, 1791: synonym of Trimusculus afer Patella alba da Costa, 1771: synonym of Patella caerulea Linnaeus, 1758Patella alba Anton, 1838: synonym of Patella caerulea Linnaeus, 1758Patella albescens Philippi, 1846: synonym of Iothia albescens Patella albida Mörch, 1853: synonym of Cymbula nigra : synonym of Cymbula safiana Patella algira Deshayes, 1840: synonym of Cymbula nigra : synonym of Cymbula safiana Patella ambigua Dillwyn, 1817: synonym of Scutus anatinus Patella amoena Say, 1822: synonym of Testudinalia testudinalis Patella amphitrite Turton, 1932: synonym of Scutellastra barbara Patella anatina Donovan, 1820: synonym of Scutus anatinus Patella ancyloides Forbes, 1840, non J de C Sowerby, 1824 and Patella exigua W. Thompson, 1844 are synonyms for Propilidium exiguum Patella apertura Montagu, 1803: synonym of Diodora graeca Patella aphanes Robson, 1986: synonym of Scutellastra aphanes Patella araucana d'Orbigny, 1839: synonym of Scurria araucana Patella ardosiaea Hombron & Jacquinot, 1841: synonym of Cellana ardosiaea Patella argenvillei Krauss, 1848: synonym of Scutellastra argenvillei Patella articulata Reeve, 1855: synonym of Cellana cylindrica Patella aspera Lamarck, 1819: synonym of Patella ulyssiponensis Gmelin, 1791Patella aster Reeve, 1855: synonym of Cellana rota Patella athletica Bean, 1844: synonym of Patella ulyssiponensis Gmelin, 1791Patella auricola da Costa, 1771: synonym of Patella depressa Pennant, 1777Patella auricularia Lightfoot, 1786: synonym of Dolabella auricularia Patella australis Lamarck, 1819: synonym of Sabia conica Patella axiaerata Verco, 1912: synonym of Asteracmea axiaerata Patella azorica Nuttal in Jay, 1852: synonym of Patella ulyssiponensis Gmelin, 1791Patella barbara Linnaeus, 1758: synonym of Scutellastra barbara Patella barbata Lamarck, 1819: synonym of Scutellastra barbara Patella baudonii Drouet, 1858: synonym of Patella ulyssiponensis Gmelin, 1791Patella bifida Fischer von Waldheim, 1807: synonym of Scutellastra barbara Patella bimaculata Montagu, 1803: synonym of Ansates pellucida : synonym of Patella pellucida Linnaeus, 1758Patella boninensis Pilsbry, 1891: synonym of Cellana mazatlandica Patella bonnardii Payraudeau, 1826: synonym of Patella ulyssiponensis Gmelin, 1791Patella borbonica Bory de Saint-Vincent, 1804: synonym of Septaria borbonica Patella caeca O. F. Müller, 1776: synonym of Lepeta caeca Patella calamus Crosse & P. Fischer, 1864: synonym of Eoacmaea calamus Patella calicula Li Chang, 1930: synonym of Patella caerulea Linnaeus, 1758Patella cancellata Risso, 1826: synonym of Patella caerulea Linnaeus, 1758Patella candeana d'Orbigny, 1847: synonym of Lottia antillarum G. B. Sowerby I, 1834Patella candida Couthouy, 1838: synonym of Lepeta caeca Patella canescens Gmelin, 1791: synonym of Cymbula canescens Patella capensis Gmelin, 1791: synonym of Cellana radiata Patella ceciliana : synonym of Scurria ceciliana Patella cernica : synonym of Cellana livescens Patella chapmani Tenison-Woods, 1875: synonym of Scutellastra chapmani Patella chinensis Linnaeus, 1758: synonym of Calyptraea chinensis Patella chitonoides Reeve, 1854: synonym of Scutellastra exusta Patella cinnamomea Gould, 1846: synonym of Phenacolepas cinnamomea Patella citrullus Gould, 1846: synonym of Patella candei d'Orbigny, 1839Patella clathratula Reeve, 1854: synonym of Cellana ardosiaea Patella clealandi Fleming, 1828: synonym of Testudinalia testudinalis Patella clypea Brown, 1827: synonym of Testudinalia testudinalis Patella clypeater Lesson, 1831: synonym of Nacella clypeater Patella cochlear Born, 1778: synonym of Scutellastra cochlear Patella coeruleata da Costa, 1778: synonym of Ansates pellucida : synonym of Patella pellucida Linnaeus, 1758Patella coffea : synonym of Scurria variabilis Patella compressa Linnaeus, 1758: synonym of Cymbula compressa Patella concolor f. polygramma Tomlin, 1931: synonym of Helcion concolor Patella conica Anton, 1838: synonym of Patella vulgata Linnaeus, 1758Patella conspicua Philippi, 1849: synonym of Cymbula nigra : synonym of Cymbula safiana Patella cornea Helbling, 1779: synonym of Ansates pellucida : synonym of Patella pellucida Linnaeus, 1758Patella costata Lesson, 1831: synonym of Fissurella costata Lesson, 1831Patella costosoplicata Mörch, 1853: synonym of Patella ferruginea Gmelin, 1791Patella crepidula Linnaeus, 1767: synonym of Crepidula unguiformis Lamarck, 1822Patella cretacea Reeve, 1854: synonym of Scutellastra flexuosa Patella cylindrica Gmelin, 1791: synonym of Cellana cylindrica Patella cypria Gmelin, 1791: synonym of Patella ferruginea Gmelin, 1791Patella cypridium Perry, 1811: synonym of Ansates pellucida : synonym of Patella pellucida Linnaeus, 1758Patella deflexa Helbling, 1779: synonym of Siphonaria deflexa