''Tetrapygus'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...
of
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) ...
s 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 ...
Arbaciidae
Arbacioida are an order of sea urchins, consisting of a single family, the Arbaciidae. They are distinguished from other sea urchins by the presence of five separate plates around the anus. Unlike their close relatives, the Salenioida, all of the ...
. It is a
monotypic
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...
genus and the only species is ''Tetrapygus niger'' which was
first described by the Chilean naturalist
Juan Ignacio Molina
Fr. Juan Ignacio Molina (; (June 24, 1740 – September 12, 1829) was a Chilean Jesuit priest, naturalist, historian, translator, geographer, botanist, ornithologist, and linguist. He is usually referred to as Abate Molina (a form of Abbot M ...
in 1782.
[ It is found in the southeastern Pacific Ocean on the coasts of South America.
]
Description
The oral (under) surface of the test
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), ...
is flattened while the aboral (upper) surface is shallowly domed. There is a small apical disc and the ambulacral areas are straight. There are up to five large primary tubercles in rows in the inter-ambulacral areas, interspersed with smaller secondary tubercles. The mouth is surrounded by a sunken subpentagonal peristome which is half as wide as the test. The primary spines are moderately long while the secondary spines are short. The colour of this sea urchin is purplish-black.
Distribution
''T. niger'' is found in the southeastern Pacific Ocean on the coasts of Peru and Chile, its range extending from northern Peru to the Strait of Magellan
The Strait of Magellan (), also called the Straits of Magellan, is a navigable sea route in southern Chile separating mainland South America to the north and Tierra del Fuego to the south. The strait is considered the most important natural pa ...
, at depths down to about . It is the most common sea urchin on this stretch of coast.
Ecology
''T. niger'' is a herbivore and grazes on the kelp
Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms.
Kelp grows in "under ...
''Lessonia trabeculata
''Lessonia trabeculata'' is a species of kelp, a brown alga in the genus '' Lessonia''. It grows subtidally off the coasts of Peru and northern and central Chile, with the closely related '' Lessonia nigrescens'' tending to form a separate zone i ...
'', the main constituent of the kelp forests on the rocky coasts of Chile. Excessive grazing by the sea urchin causes lack of recruitment of the kelp because the sea urchin completely consumes young plants, while it only feeds on the stipe (stalk) of older plants.
Starfish including ''Luidia magellanica
''Luidia magellanica'' is a species of starfish in the family Luidiidae. It is found in the southeastern Pacific Ocean on the coast of South America.
Distribution and habitat
''Luidia magellanica'' occurs subtidally in the southeastern Pacifi ...
'', ''Meyenaster gelatinosus
''Meyenaster'' is a genus of starfish in the family Asteriidae. It is a monotypic genus and the only species is ''Meyenaster gelatinosus'' which was first described by the Prussian botanist and zoologist Franz Julius Ferdinand Meyen in 1834. I ...
'', ''Stichaster striatus
''Stichaster striatus'', the common light striated star, is a species of starfish in the family Stichasteridae, found in the southeastern Pacific Ocean. It was first described by the German zoologists Johannes Peter Müller and Franz Hermann ...
'' and ''Heliaster helianthus
The sun star ''(Heliaster helianthus)'' is a species of Asteroidea (starfish) in the family Heliasteridae. It is found in shallow water rocky habitats and in the kelp forests off the Pacific coast of Ecuador, Peru and Chile.
Description
''H. h ...
'' prey heavily on grazing herbivores such as ''T. niger''.El Niño
El Niño (; ; ) is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date ...
.urchin barren
An urchin barren is an area of the shallow part of the ocean where the population growth of sea urchins has gone unchecked, causing destructive grazing of kelp forests.
Process
Sea urchins eat kelp holdfasts. This can be caused by a lack of sea ...
s" with no macro-algae and limited biodiversity, the rocks being covered with encrusting 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 r ...
.
References
{{Taxonbar, from=Q3519178, from2=Q3203595
Asteriidae
Monotypic genera