''Ctenella'' is a monotypic genus of stony coral 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 ...

Euphylliidae. It is represented by a single species, ''Ctenella chagius''. These corals are massive in size with meandering valleys between the calyces which have solid, non-porous walls and fine, evenly spaced, solid septae.Family Meandrinidae
Classification of Scleractinian (Stony) Corals. Retrieved 2012-11-10. They are found in the

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

being endemic to the

Chagos Archipelago The Chagos Archipelago (, ) or Chagos Islands (formerly , and later the Oil Islands) is a group of seven atolls comprising more than 60 islands in the Indian Ocean about south of the Maldives archipelago. This chain of islands is the southernmo ...

. It forms solid, smooth hemispherical domes.

Description

''Ctenella chagius'' is a massive, hemispherical, colonial coral with a fissured surface and brain-like appearance. The individual polyps that secrete the stony skeleton project from stony cups called

corallite A corallite is the skeletal cup, formed by an individual stony coral polyp, in which the polyp sits and into which it can retract. The cup is composed of aragonite, a crystalline form of calcium carbonate, and is secreted by the polyp. Corallit ...

s arranged in rows in long meandering valleys. The width between the solid ridges on either side is about with the valleys being about deep. The fine

septa SEPTA, the Southeastern Pennsylvania Transportation Authority, is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly four million people througho ...

that radiate from the corallites are closely packed and evenly spaced, some continuing upwards and over the ridges.Family Meandrinidae
Classification of Scleractinian (Stony) Corals. Retrieved 2012-11-20. This coral is a pale brown colour and can grow to a metre (yard) in diameter. It is a zooxanthellate coral and has

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

unicellular

dinoflagellate The Dinoflagellates (), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered protists. Dinoflagellates are mostly marine plankton, but they are also commo ...

algae living within its tissues.

Distribution

''Ctenella chagius'' is found around the Chagos Islands. It is found in

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...

s and on

reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...

slopes at depths of up to .

Status

''Ctenella chagius'' is listed as being "

critically endangered An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...

" in the

IUCN Red List of Threatened Species The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological spe ...

. The size of its population is unknown but the reefs on which it lives are being degraded at a faster rate than it is likely to be able to establish new colonies. It is very susceptible to

coral bleaching Coral bleaching is the process when corals become white due to loss of Symbiosis, symbiotic algae and Photosynthesis, photosynthetic pigments. This loss of pigment can be caused by various stressors, such as changes in water temperature, light, ...

and coral diseases, both of which are on the increase as sea temperatures rise. There are also threats to the coral from human activities but the Chagos Islands are now part of the

Chagos Marine Protected Area The Chagos Marine Protected Area, located in the central Indian Ocean in the British Indian Ocean Territory of the United Kingdom, is one of the world's largest officially designated marine protected areas, and one of the List of largest protecte ...

which should provide a measure of protection for this coral.

References

{{Taxonbar, from1=Q5191613, from2=Q3330213 Scleractinia genera Euphylliidae Animals described in 1928 Monotypic cnidarian genera