Meoma Ventricosa
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''Meoma ventricosa'', known by the common names cake urchin and red heart urchin, is a large
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
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 ...
which lives in shallow waters in the Caribbean. It may reach a diameter of twenty centimeters and is covered in reddish-brown spines. It has both pentagonal
radial symmetry Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, the face of a human being has a plane of symme ...
and bilateral symmetry, giving it a sand-dollar appearance; however, two of its five sections are merged more closely than the others.


Subspecies

There are two subspecies: *''Meoma ventricosa grandis'' Gray, 1851 *''Meoma ventricosa ventricosa'' (Lamarck, 1816)


Description

The red heart urchin has a somewhat flattened, heart-shaped test made of closely fitting,
calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
plates. These are covered by short, dense, moveable spines situated on small tubercles. The test is a dark reddish-brown colour and the spines a little paler. Although it has pentagonal radial symmetry, it also has some degree of bilateral symmetry as one of the interambulacral areas is undeveloped and only four are apparent. The mouth is on the oral (under) surface near the
anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
end and the anus at the posterior end.


Distribution and habitat

The red heart urchin is found in the
Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...
, the
Bahamas The Bahamas, officially the Commonwealth of The Bahamas, is an archipelagic and island country within the Lucayan Archipelago of the Atlantic Ocean. It contains 97 per cent of the archipelago's land area and 88 per cent of its population. ...
,
Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...
and
Bermuda Bermuda is a British Overseas Territories, British Overseas Territory in the Atlantic Ocean, North Atlantic Ocean. The closest land outside the territory is in the American state of North Carolina, about to the west-northwest. Bermuda is an ...
. It inhabits reef flats, turtle grass beds, areas of coral fragments and deep reefs. It buries itself in the seabed choosing to inhabit sedimentary areas with sand, silt or coarse coral rubble. Its depth range is
intertidal The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various sp ...
down to .


Biology

Each sand grain in the marine environment has a
film A film, also known as a movie or motion picture, is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, emotions, or atmosphere through the use of moving images that are generally, sinc ...
of
alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...
e and
bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
growing on its surface. The red heart urchin feeds on these films by swallowing sediment while it
burrow file:Chipmunk-burrow (exits).jpg, An eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of Animal lo ...
s under the surface of 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 ...
. Fifty six
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 ...
situated near the mouth form a disc and
mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...
causes the sand particles to adhere to it. The disc is then retracted into the mouth and the particles swallowed. They are passed through the gut and the nutritive matter extracted in the process. The urchin's growth rate is slow as it is limited both by the amount of organic material that can be extracted in this way and also by the lack of oxygen in the sediment, especially at night. To overcome this limitation, adult urchins often emerge onto the seabed at night and burrow down into the sediment again next day while juveniles remain permanently buried. During feeding, the large urchins disturb the substrate and increase its water content while decreasing its density. This has a considerable impact on the
microhabitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
and may be beneficial for the urchin as it results in an increase in the growth of the algae and bacteria forming the film round the particles of sediment. The red heart urchin has few
predators Predation is a biological interaction in which 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 ...
but is sometimes preyed on by
stingray Stingrays are a group of sea Batoidea, rays, a type of cartilaginous fish. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatidae (deepwate ...
s and other fish,
loggerhead turtle The loggerhead sea turtle (''Caretta caretta'') is a species of oceanic turtle distributed throughout the world. It is a marine reptile, belonging to the family Cheloniidae. The average loggerhead measures around in carapace length when ful ...
s and the
sea star Starfish or sea stars are Star polygon, star-shaped echinoderms belonging to the class (biology), class Asteroidea (). Common usage frequently finds these names being also applied to brittle star, ophiuroids, which are correctly referred to ...
''
Oreaster reticulatus ''Oreaster reticulatus'', commonly known as the red cushion sea star or the West Indian sea star, is a species of marine invertebrate, a starfish in the family Oreasteridae. It is found in shallow water in the western Atlantic Ocean and the Cari ...
''. It can emit a noxious yellow exudate which repels fish and may even kill them. Several red heart urchins may aggregate and the progress of each one through the sediment can be observed by a depressed trail left behind as it progresses and a slight mound of coarser material above it. Red heart urchins burrow at the rate of an hour during the day and twice as fast as this at night. In 1997, an
epizootic In epizoology, an epizootic (or epizoötic, from Greek: ''epi-'' "upon" + ''zoon'' "animal") is a disease event in a nonhuman animal population analogous to an epidemic in humans. An epizootic disease (or ) may occur in a specific locale (an ...
event involving the red heart urchin occurred off the coast of
Curaçao Curaçao, officially the Country of Curaçao, is a constituent island country within the Kingdom of the Netherlands, located in the southern Caribbean Sea (specifically the Dutch Caribbean region), about north of Venezuela. Curaçao includ ...
. It was established that the causative agent was a species of
bacterium Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...
, ''
Pseudoalteromonas ''Pseudoalteromonas'' is a genus of marine bacteria. In 1995, Gauthier ''et al'' proposed ''Pseudoalteromonas'' as a new genus to be split from ''Alteromonas''. The ''Pseudoalteromonas'' species that were described before 1995 were originally par ...
''. Affected urchins lost their spines and later died. It was found that the disease was largely confined to an area of a few square kilometres down-current from
Willemstad Willemstad ( ; ; ; ) is the capital city, capital and largest city of Curaçao, an island in the southern Caribbean Sea that is a Countries of the Kingdom of the Netherlands, constituent country of the Kingdom of the Netherlands. It was the cap ...
harbour. It was suggested that polluted water caused an increase in bacteria-laden sediment and that consumption of this by the urchins caused their deaths. In Florida, breeding takes place in the winter between August and February peaking between November and January.
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 ...
is not synchronized and fertilisation takes place in 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 ...
. The larvae are
plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...
ic and settle on the seabed in suitable sandy locations, perhaps guided there by chemical cues. Most adults have a
parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...
relationship with one or more small
crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...
s of the species '' Dissodactylus primitivus''. The crab lives on the urchin, usually inside or near its mouth.


References


External links

* {{Taxonbar, from=Q2785148 Spatangoida Echinoderms described in 1816 Echinoderms of the Atlantic Ocean