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

sea urchin Sea urchins or urchins () are echinoderms in the class (biology), class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of . They typically have a globular body cove ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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

. It is found in subtidal regions in temperate seas throughout 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 projectio ...

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 tha ...

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 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 or tubes may refer to: * Tube (2003 film), ''Tube'' (2003 film), a 2003 Korean film * "Tubes" (Peter Dale), performer on the Soccer AM#Tubes, Soccer AM television show * Tube (band), a Japanese rock band * Tube & Berger, the alias of dance/e ...

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

Taxonomy

The species was first described as ''Echinus cordatum'' in 1777 by

Thomas Pennant Thomas Pennant (16 December 1798) was a Welsh natural history, naturalist, traveller, writer and antiquarian. He was born and lived his whole life at his family estate, Downing Hall, near Whitford, Flintshire, in Wales. As a naturalist he had ...

. It has subsequently been synonymised with ''Echinocardium sebae''

Gray Grey (more frequent in British English) or gray (more frequent in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning that it has no chroma. It is the color of a cloud-covered s ...

, 1825, ''Spatangus arcuarius''

Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist, biologist, academic, and soldier. He was an early proponent of the idea that biolo ...

, 1816, ''Echinocardium australe'' Gray, 1851, ''Echinocardium stimpsonii'' A. Agassiz, 1864, ''Echinocardium zealandicum'' Gray, 1851, ''Amphidetus novaezelandiae'' Perrier, 1869, and ''Amphidetus kurtzii'' Girard, 1852.

Distribution

The sea potato has a discontinuous

cosmopolitan distribution In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

. It is reported from

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

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.World Register of Marine Species
/ref> 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, . 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-illuminate ...

.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 ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

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. Like most other urchins, male and female sea potatoes reproduce via broadcast

spawning Spawn is the Egg cell, eggs and Spermatozoa, sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of freely releasing eggs and sperm into a body of water (fresh or marine); the physical act is ...

, meaning that they release

gametes A gamete ( ) 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. The name gamete was introduced by the Ge ...

directly into the

water column The (oceanic) water column is a concept used in oceanography to describe the physical (temperature, salinity, light penetration) and chemical ( pH, dissolved oxygen, nutrient salts) characteristics of seawater at different depths for a defined ...

, where fertilization occurs. The echinoplutei

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

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. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

and form part of the

zooplankton Zooplankton are the heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

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

takes place about 39 days after fertilisation with the larvae settling out and burrowing into the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

. 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 () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

molluscs Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

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 be ...

'', '' Ensis ensis'' and '' Venus striatula''. The bivalve '' Tellimya ferruginosa'' 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 f ...

. 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 (Mytili ...

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 10,700 amphipod species cur ...

crustacean, '' Urothoe marina''.

Gallery

Ecomare - zeeklit (zeeklit-4321-ogb).jpg Ecomare - zeeklit (5019-strand-zeeklit-ogb).jpg

In culture

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

West Cork West Cork () 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, Castletownbere, Clonakilty, Du ...

Ireland Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...

, 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 was a first-century Jewish woman of Nazareth, the wife of Saint Joseph, Joseph and the mother of Jesus. She is an important figure of Christianity, venerated under titles of Mary, mother of Jesus, various titles such as Perpetual virginity ...

. 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 on 1 November 1950 in his apostolic constitution as follows: It leaves open the question of whether Mary died or whether she was ra ...

External links

Echinocardium cordatum: occurrence data and images
from

GBIF The Global Biodiversity Information Facility (GBIF) is an international organisation that focuses on making scientific data on biodiversity available via the Internet using web services. The data are provided by many institutions from around the ...

References

{{Taxonbar, from=Q838252 Spatangoida Echinoderms of the Atlantic Ocean Echinoderms of the Indian Ocean Echinoderms of the Pacific Ocean Animals described in 1777 Taxa named by Thomas Pennant