Septum (coral)

Last updated February 21, 2019

In corals, a septum (plural septa) is one of the radiating vertical plates lying within the corallite wall. Outside the corallite wall these plates are known as costae (singular costa).^[1] 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.^[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 costa is one of the vertical plates lying outside the corallite wall, a continuation of a septum which lies inside the wall. 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.

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In biology, a septum is a wall, dividing a cavity or structure into smaller ones.

Septa may refer to:

Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a mouth is fringed with tentacles. Although some species are solitary, most are colonial. The founding polyp settles and starts to secrete calcium carbonate to protect its soft body. Solitary corals can be as much as 25 cm (10 in) across but in colonial species the polyps are usually only a few millimetres in diameter. These polyps reproduce asexually by budding, but remain attached to each other, forming a multi-polyp colony of clones with a common skeleton, which may be up to several metres in diameter or height according to species.

The Rugosa, also called the Tetracorallia, are an extinct order of solitary and colonial corals that were abundant in Middle Ordovician to Late Permian seas.

Astreopora is a genus of stony corals in the Acroporidae family. Members of the genus are commonly known as star corals and there are seventeen species currently recognized.

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.

The Agariciidae are a family of reef-building stony corals. This family includes cactus corals, plate corals, and lettuce corals. Members of the family include symbiotic algae called zooxanthellae in their tissues which help provide their energy requirements.

Isastrea is an extinct genus of corals that lived during the Jurassic and Cretaceous periods. Its fossils have been found in Europe, Africa, North America, Asia and South America.

Stylophora pistillata, commonly known as hood coral or smooth cauliflower coral, is a species of stony coral in the family Pocilloporidae. It is native to the Indo-Pacific region and is commonly used in scientific investigations.

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.

Meandrina meandrites, commonly known as maze coral, is a species of colonial stony coral in the family Meandrinidae. It is found primarily on outer coral reef slopes in the Caribbean Sea and the Gulf of Mexico.

Astrangia solitaria, the dwarf cup coral or southern cup coral, is a species of stony coral in the family Rhizangiidae. It is native to shallow water in the western Atlantic Ocean and the Caribbean Sea.

Turbinaria is a genus of colonial stony corals in the family Dendrophylliidae. Common names for this genus include disc coral, scroll coral, cup coral, vase coral, pagoda coral and ruffled ridge coral. These corals are native to the Red Sea, Indian Ocean, Japan and the south Central Pacific Ocean.

Turbinaria peltata, commonly known as disc coral, is a species of colonial stony coral in the family Dendrophylliidae. It is native to the Indo-Pacific region. The International Union for Conservation of Nature has rated its conservation status as being "vulnerable".

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.

Stylophora madagascarensis is a species of stony coral in the family Pocilloporidae. It is native to the tropical western Indian Ocean where it is confined to the coasts of Madagascar, growing in shallow water.

References

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