A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral end is attached to the substrate by means of a disc-like holdfast called a pedal disc, while in colonies of polyps it is connected to other polyps, either directly or indirectly. The oral end contains the mouth, and is surrounded by a circlet of tentacles.
Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.
Anthozoa is a class of marine invertebrates which includes sessile cnidarians such as the sea anemones, stony corals, soft corals and sea pens. Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as planktons. The basic unit of the adult is the polyp; this consists of a cylindrical column topped by a disc with a central mouth surrounded by tentacles. Sea anemones are mostly solitary, but the majority of corals are colonial, being formed by the budding of new polyps from an original, founding individual. Colonies are strengthened by calcium carbonate and other materials and take various massive, plate-like, bushy or leafy forms.
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.
Madrepora is a genus of stony corals, often found forming reefs or islands in tropical locations. The names Madrepore and Madreporaria were formerly applied universally to any stony coral of the family Scleractinia. They reproduce in three separate ways, as discovered by the marine zoologist Anne Thynne (1800–1866). It is commonly known as horn coral. A colony is branched with small polyps in cylindrical cups separated by a perforated coenosteum. Terminal polyps bear six tentacles, while lateral polyps bear twelve tentacles. Madrepora is economically important, since it contributes to the formation of coral reefs.
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.
Mussidae is a family of stony coral in the order Scleractinia. Following a taxonomic revision in 2012, the family is now restricted to species found in the Atlantic Ocean, with Pacific species transferred to the new family Lobophylliidae. Many species are referred to as brain coral because their generally spheroid form and grooved surface resembles the convolutions of a brain.
Octocorallia is a class of Anthozoa comprising over 3,000 species of marine organisms formed of colonial polyps with 8-fold symmetry. It includes the blue coral, soft corals, sea pens, and gorgonians within three orders: Alcyonacea, Helioporacea, and Pennatulacea. These organisms have an internal skeleton secreted by mesoglea and polyps with eight tentacles and eight mesentaries. As with all cnidarians these organisms have a complex life cycle including a motile phase when they are considered plankton and later characteristic sessile phase.
A gonophore is a reproductive organ in members of the Hydrozoa which produces gametes. It is a sporosac, a medusa or any intermediate stage. The name is derived from the Greek words γόνος and -φόρος.
Oculinidae is a family of colonial corals.
Poritidae is a family of stony corals. Members of the family are colonial hermatypic (reef-building) corals. They are variable in size and form but most are massive, laminar or ramose as well as branching and encrusting. The corallites are compact with very little coenosteum covering the skeleton. The walls of the corallites and the septa are porous. J.E.N. Veron considers the family is not a natural grouping but is a miscellaneous collection of genera that do not fit well elsewhere.
Porites lobata, known by the common name lobe coral, is a species of stony coral in the family Poritidae. It is found growing on coral reefs in tropical parts of the Indian and Pacific Oceans.
Millepora alcicornis, or sea ginger, is a species of colonial fire coral with a calcareous skeleton. It is found on shallow water coral reefs in the tropical west Atlantic Ocean. It shows a variety of different morphologies depending on its location. It feeds on plankton and derives part of its energy requirements from microalgae found within its tissues. It is an important member of the reef building community and subject to the same threats as other corals. It can cause painful stings to unwary divers.
Eusmilia is a genus of stony coral in the family Meandrinidae. It is a monotypic genus represented by the species Eusmilia fastigiata, commonly known as the smooth flower coral. It is found on reefs in the Caribbean Sea.
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 reniformis, commonly known as yellow scroll 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".
In corals, the coenosteum is the stony skeletal material secreted by the coenosarc, the layer of living material lying between the corallites. The coenosteum is composed of aragonite, a crystalline form of calcium carbonate, and is generally a spongy, porous material. Sometimes the coenosteum has ornamentation such as ridges and beads, visible as raised areas of the coenosarc. The coenosteum and corallites together are known as the corallum.
Madracis auretenra, commonly known as the yellow finger coral or yellow pencil coral, is a colonial species of stony coral in the family Pocilloporidae. It is a fairly common species and is found in the Caribbean Sea and western Atlantic Ocean. At one time this species was not recognised, but it was split from Madracis mirabilis on the grounds of morphology and depth range.
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.
