''Echinocardium cordatum'', also known as the common heart urchin or the sea potato, is a

sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...

in the

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

Loveniidae Loveniidae is a family of heart urchins in the order Spatangoida. Description and characteristics These sea urchins are called "heart urchins" due to their specific shape, looking like a heart when seen from below (more or less depending on th ...

. It is found in sub-tidal regions in the NE Atlantic. Other un-named species have been identified as this species from temperate seas around the world. It lives buried in the sandy sea floor.

Description

The sea potato is a heart-shaped urchin clothed in a dense mat of furrowed yellowish spines which grow from

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection ...

s and mostly point backwards. The upper surface is flattened and there is an indentation near the front. This urchin is a fawn colour but the

tests Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film), ...

that are found on the

strandline A high water mark is a point that represents the maximum rise of a body of water over land. Such a mark is often the result of a flood, but high water marks may reflect an all-time high, an annual high (highest level to which water rose that ...

have often lost their spines and are white. During life, the spines trap air which helps prevent asphyxiation for the buried urchin.European Marine Life
/ref> The

ambulacra Ambulacrum is an architectural word that denotes an atrium, courtyard, or parvise in front of a basilica or church that is surrounded by arcades or colonnades, or trees, and which often contains a fountain A fountain, from the Latin "fon ...

form a broad furrow in a star shape extending down the sides of the test. There are two series each of two rows of

tube feet Tube feet (technically podia) are small active tubular projections on the oral face of an echinoderm, whether the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on britt ...

. The test reaches from six to nine centimetres in length.

Distribution

The sea potato has a discontinuous

cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...

. It is reported from

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

seas in the north Atlantic Ocean, the west Pacific Ocean, around Australia, New Zealand, South Africa and the Gulf of California at depths of down to 230 metres. A 2016 study revealed that it was a complex of at least 5 species, with three in Europe, one in Australia and one in the NW Pacific.E. Egea, B. David, T. Choné, B. Laurin, J.P. Féral, A. Chenuil, (2016) Morphological and genetic analyses reveal a cryptic species complex in the echinoid ''Echinocardium cordatum'' and rule out a stabilizing selection explanation. Molecular Phylogenetics and Evolution, Volume 94, Part A, Pages 207-220, ISSN 1055-7903, https://doi.org/10.1016/j.ympev.2015.07.023. It is very common round the coasts of the British Isles in the

neritic zone The neritic zone (or sublittoral zone) is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology it forms a relatively stable and well-illuminated ...

.National Museums of Northern Ireland
/ref>

Biology

The sea potato buries itself in sand to a depth of ten to fifteen centimetres. It occurs in sediments with a wide range of grain sizes but prefers sediments with a size of 200 to 300 µm and a low mud content. It makes a respiratory channel leading to the surface and two sanitary channels behind itself, all lined by a mucus secretion. The location of burrows can be recognised by a conical depression on the surface in which

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

collects. This organic debris is used by the buried animal as food and is passed down by means of the long tube feet found in the front of the ambulacrum. The sexes are separate in the sea potato and the males and females both liberate

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

s into the

water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. T ...

in the spring. The echinoplutei

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e that develop after fertilisation have four pairs of arms and are laterally flattened. In late stage larvae, tube feet may be seen developing round the skeleton. The

e are

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

and form part of the

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

Metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

takes place about 39 days after fertilisation with the larvae settling out and burrowing into the substrate. The lifespan of the sea potato is thought to be ten or more years.

Ecology

In the sandy sea bed that it favours, the sea potato is often found in association with the

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

molluscs 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 taxon, extant species of molluscs are recognized. The number of fossil sp ...

Tellina fabula ''Fabulina fabula'', the bean-like tellin, is a species of marine bivalve mollusc in the family Tellinidae. It is found off the coasts of northwest Europe, where it lives buried in sandy sediments. Bivalves are molluscs with a body compressed ...

'', ''

Ensis ensis ''Ensis ensis'', or the sword razor, is a razor clam, a marine bivalve mollusc in the family Pharidae. It lives buried in the sand and is found off the coasts of northwest Europe. Description The two valves that make up the shell of ''Ensis ens ...

'' and '' Venus striatula''. The bivalve ''

Tellimya ferruginosa ''Tellimya ferruginosa'' is a species of small marine bivalve mollusc in the family Lasaeidae. It is found on the eastern side of the Atlantic Ocean. Bivalves are molluscs with a body compressed between two usually similar shell valves joined ...

'' is often found living inside the sea potato's burrow as a

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

. Up to fourteen have been found in one burrow with the young being attached to the spines of the urchin by

byssus A byssus () is a bundle of filaments secreted by many species of bivalve mollusc that function to attach the mollusc to a solid surface. Species from several families of clams have a byssus, including pen shells (Pinnidae), true mussels (Mytilid ...

threads. Another species that makes use of the burrow is the

amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descr ...

crustacean, ''

Urothoe marina ''Urothoe marina'' is a species of small marine amphipod crustaceans in the family Urothoidae. It is found on and burrowing in coarse sediments in shallow coastal waters off northwestern Europe. Description ''U. marina'' is about long, cresce ...

''.

In Culture

The test (shell) of the sea potato has cultural significance in

West Cork West Cork ( ga, Iarthar Chorcaí) is a tourist region and municipal district in County Cork, Ireland. As a municipal district, West Cork falls within the administrative area of Cork County Council, and includes the towns of Bantry, Castletownbe ...

Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...

, where it is traditionally referred to as a "Virgin Mary" shell. According to traditional belief, the distinct patterns visible on the test are thought to resemble an apparition of the

Virgin Mary Mary; arc, ܡܪܝܡ, translit=Mariam; ar, مريم, translit=Maryam; grc, Μαρία, translit=María; la, Maria; cop, Ⲙⲁⲣⲓⲁ, translit=Maria was a first-century Jewish woman of Nazareth, the wife of Joseph and the mother o ...

. There is also a traditional association between the appearance of the shells on beaches in West Cork and the Marian month of May and the

Feast of the Assumption The Assumption of Mary is one of the four Marian dogmas of the Catholic Church. Pope Pius XII defined it in 1950 in his apostolic constitution ''Munificentissimus Deus'' as follows: We proclaim and define it to be a dogma revealed by Go ...

References

Ecomare - zeeklit (zeeklit-4321-ogb).jpg Ecomare - zeeklit (5019-strand-zeeklit-ogb).jpg {{Taxonbar, from=Q838252 Spatangoida Fauna of the Atlantic Ocean Fauna of the Indian Ocean Fauna of the Pacific Ocean Animals described in 1777 Taxa named by Thomas Pennant