Costa (coral)

Last updated March 21, 2019

In corals, a costa (plural costae) is one of the vertical plates lying outside the corallite wall, a continuation of a septum (plural septa) which lies inside the wall.^[1] The costae may continue to the edge of the colony and in solitary species, such as those in the family Fungiidae, refers to the ridges on the underside of the coral.^[2]

Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically live in compact colonies of many identical individual polyps. Corals species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.

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. Corallites vary in size, but in most colonial corals they are less than 3 mm (0.12 in) in diameter. The inner surface of the corallite is known as the calyx. The vertical blades inside the calyx are known as septa and in some species, these ridges continue outside the corallite wall as costae. Where there is no corallite wall, the blades are known as septocostae. The septa, costae and septocostae may have ornamentation in the form of teeth and may be thick, thin or variable in size. Sometimes there are paliform lobes, in the form of rods or blades, rising from the inner margins of the septa. These may form a neat circle called the paliform crown. The septa do not usually unite in the centre of the corallite, instead they form a columella, a tangled mass of intertwined septa, or a dome-shaped or pillar-like projection. In the living coral, the lower part of the polyp is in intimate contact with the corallite, and has radial mesenteries between the septa which increase the surface area of the body cavity and aid digestion. The septa, palliform lobes and costae can often be seen through the coenosarc, the layer of living tissue that covers the coenosteum, the part of the skeleton between the corallites.

In corals, a septum is one of the radiating vertical plates lying within the corallite wall. Outside the corallite wall these plates are known as costae. The septa may be thick, thin or vary in size. They may have teeth which range from needle-like to blade-like and are often characteristic of different genera.

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Septa may refer to:

Favia is a genus of reef-building stony corals in the family Mussidae. Members of the genus are massive or thickly encrusting colonial corals, either dome-shaped or flat, and a few are foliaceous. There is a great diversity of form even among individuals of the same species. The corallites project slightly above the surface of the coral and each has its own wall. In most species, the corallites are plocoid and in some, monocentric. The septa and costae linked to the corallite wall are well developed and covered by fine teeth. The polyps only extend and feed during the night. Each one has a small number of tapering tentacles which often have a darker coloured tip; these are called stinger tentacles, or sweeper tentacles. They use these to sweep the water to see if any other coral is in its area; if so, then they begin to sting the other coral. This is commonly known as coral war. Each coral is trying to make sure it has enough room around it so they can continue to grow and have more surface area for their offspring. The columella is parietal and spongy, and there are vesicles on both the endotheca and exotheca. Members of this genus are widespread in both the Atlantic Ocean and the Indo-Pacific.

Fungia is a genus of corals in the family Fungiidae. It is monotypic with the single species Fungia fungites, which is found growing on reefs in the Indo-Pacific.

Cycloseris is a genus of solitary disc corals in the family Fungiidae. They are found in the Indo-Pacific. They inhabit the lower reef slopes, and the areas between reefs with soft sediments. They tolerate turbid waters.

Sandalolitha robusta is a plate or mushroom coral in the family Fungiidae. This coral is found in the Indo-Pacific region.

Pleuractis paumotensis, commonly called plate coral, is a species of stony coral with a single large polyp. Plate coral are commonly kept in marine aquaria.

Lobactis is a genus of plate or mushroom coral in the family Fungiidae. The genus is monotypic with a single species, Lobactis scutaria, that is found in the Indo-Pacific region.

Favia fragrum is a species of colonial stony coral in the family Mussidae. It is commonly known as the golfball coral and is found in tropical waters on either side of the Atlantic Ocean.

<i>Plerogyra sinuosa</i> species of cnidarian

Plerogyra sinuosa is a species of "bubble coral". It has grape-sized bubbles which increase their surface area according to the amount of light available: they are larger during the day, but smaller during the night, when tentacles reach out to capture food. This species requires low light and a gentle water flow. Common names for Plerogyra sinuosa include "grape coral", bladder coral, pearl coral and branching bubble coral.

Pseudodiploria strigosa, the symmetrical brain coral, is a colonial species of stony coral in the family Mussidae. It occurs on reefs in shallow water in the West Atlantic Ocean and Caribbean Sea. It grows slowly and lives to a great age.

Pseudodiploria clivosa, the knobby brain coral, is a colonial species of stony coral in the family Mussidae. It occurs in shallow water in the West Atlantic Ocean and Caribbean Sea.

Dipsastraea speciosa is a species of colonial stony coral in the family Merulinidae. It is found in tropical waters of the Indian and Pacific oceans.

Ctenactis is a genus of solitary disc corals in the family Fungiidae. Members of this genus are found in the Indo-Pacific region.

Favites complanata is a species of stony coral in the family Merulinidae, sometimes known as the larger star coral. It is native to the Indo-Pacific region and its range extends from the Red Sea and Indian Ocean to the western and central Pacific Ocean. This is an uncommon species of coral and seems to be decreasing in abundance, and the International Union for Conservation of Nature has rated its conservation status as being "near threatened".

Oxypora lacera, the ragged chalice coral or porous lettuce coral, is a species of large polyp stony corals in the family Lobophylliidae. It is a colonial coral which can be submassive, encrusting or laminar. It is native to the western Indo-Pacific.

Echinophyllia aspera, commonly known as the chalice coral, is a species of large polyp stony corals in the family Lobophylliidae. It is a colonial coral which is partly encrusting and partly forms laminate plates or tiers. It is native to the western and central Indo-Pacific.

Horastrea is a monotypic genus of stony coral in the family Coscinaraeidae. It is represented by the single species Horastrea indica, the blister coral. It is native to the southwestern Indian Ocean where it is found in shallow water sandy reefs. It was first described by M Pichon in 1971. It is an uncommon coral and the International Union for Conservation of Nature has assessed it as being a "vulnerable species".

References

↑ Sprung, Julian (1999). Corals: A quick reference guide. Ricordea Publishing. pp. 220–223. ISBN 1-883693-09-8.
↑ "Costae". Coral Hub. Retrieved 2015-04-22.

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[1] Sprung, Julian (1999). Corals: A quick reference guide. Ricordea Publishing. pp. 220–223. ISBN 1-883693-09-8.

[2] "Costae". Coral Hub. Retrieved 2015-04-22.