''Scutellastra longicosta'', the long-spined limpet or the duck's foot limpet, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

true limpet The Patellogastropoda, common name true limpets and historically called the Docoglossa, are members of a major phylogenetic group of marine gastropods, treated by experts either as a clade or as a taxonomic order. The clade Patellogastropoda ...

, a marine gastropod

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Patellidae Patellidae is a taxonomic family of sea snails or true limpets, marine gastropod molluscs in the clade Patellogastropoda. (The superfamily Patelloidea should not be confused with the similar-sounding genus of true limpets '' Patelloida'' which ...

, one of the families of true limpets. It is native to the coasts of South Africa where it is found on the foreshore. It cultivates a species of crustose brown algae in a "garden".

Description

''Scutellastra longicosta'' has about eleven long, spiked ribs giving it a star-shaped outline. It grows to a diameter of about . The inner surface is glossy white or bluish-white and often has a narrow black rim.

Distribution and habitat

This species can be found on the eastern and southern coasts of

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

. Its range extends from

Richards Bay Richards Bay ( af, Richardsbaai) is a town in KwaZulu-Natal, South Africa. It is situated on a 30 square kilometre lagoon of the Mhlatuze River, which makes it one of the country's largest harbours. Richards Bay also has the deepest natural h ...

round

Cape Province The Province of the Cape of Good Hope ( af, Provinsie Kaap die Goeie Hoop), commonly referred to as the Cape Province ( af, Kaapprovinsie) and colloquially as The Cape ( af, Die Kaap), was a province in the Union of South Africa and subsequen ...

to the Cape of Good Hope. It is found in the mid-to-lower intertidal zone on rocky surfaces.

Behaviour

''Scutellastra longicosta'' is a

territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...

limpet occupying a permanent position and cultivating the brown alga '' Ralfsia verrucosa'' in a "garden" which it defends from other

herbivores A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

. The productivity of the cultivated algae is about 30% higher than it is when the algae grow elsewhere. It has been shown that ''

Scutellastra cochlear ''Scutellastra cochlear'' is a species of sea snail, a marine gastropod mollusc in the family Patellidae, one of the families of true limpets. It is commonly known as the snail patella, the pear limpet or the spoon limpet and is native to Sout ...

'', a closely related limpet, fertilises its algal garden with

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...

that accumulates round the rim of its shell when the limpet is exposed to the air at low tide and this may also be the case with ''Scutellastra longicosta''. The cultivation of the garden is a form of mutualism as both limpet and alga derive benefit from the arrangement. Larvae of ''Scutellastra longicosta'' tend to settle on the shells of larger limpets and the juveniles graze the encrusting alga that grows there. When they are large enough they move onto the rocks and graze on

coralline algae Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of ...

before eventually setting up their own gardens. These are established by grazing hard to remove any algae growing on a rock surface and allowing settlement of ''R. verrucosa'', this limpet's favoured food. The algal growth is then regularly grazed and maintained as turf, being fertilised by the limpet's faeces and by mucus. The garden is defended from other herbivores which the limpet pries off the surface with its spines. A limpet can "farm" an area of about , occupies a scar near the centre, and seldom moves out of this area. Gardens seldom overlap and even though the limpet is encouraging the growth of a single species of alga, there may be greater algal diversity in the area than might otherwise occur. This is because, while defending their gardens, the limpets drive off herbivores from the patches of rock between their gardens, giving algae settling there a greater chance of flourishing. Limpets experimentally removed from their territories and transplanted to nearby locations were found to have homing abilities and find their way back to their original gardens. Various

predators Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

feed on this limpet, especially the

African oystercatcher The African oystercatcher or African black oystercatcher (''Haematopus moquini''), is a large charismatic wader resident to the mainland coasts and offshore islands of southern Africa. This near-threatened oystercatcher has a population of over ...

References

{{DEFAULTSORT:Scutellastra Longicosta Patellidae Gastropods described in 1819 Invertebrates of South Africa Taxa named by Jean-Baptiste Lamarck