What animal is coral?

Coral is a general term for coelenterates. In our daily life, coral is one of the important organic gems. Everything with strange shape and exquisite appearance is called "coral", and everything with red color is called "red coral". Corals usually include soft corals, gorgonian corals, red corals, stony corals, horny corals, corals, light-colored corals and coral reefs. Some people mistakenly call soft gills and colony anemones "corals". Coral is a kind of marine cylindrical coelenterate named "Coral". In the white larval stage, it is automatically fixed on the calcareous remains of ancestral corals. The chemical composition of coral is mainly CaCO3, which exists in the form of microcrystalline calcite aggregate with a certain amount of organic matter. Most of them are dendritic with longitudinal stripes on them. Each coral has concentric circles and radial stripes in its cross section. The color is often white, but there are also a little blue and black. Gem-grade corals are red, pink and orange. Red is formed because coral absorbs about 1% iron oxide in seawater during its growth, and black is formed because it contains organic matter. It has glass luster to waxy luster, opaque to translucent, and the refractive index is 1.48- 1.66. The hardness is 3.5-4, the density is 2.6-2.7g/cm3, and the density of black coral is relatively low, which is 1.34g/cm3. Sexually fragile. Strong foaming in hydrochloric acid. No fluorescence. The ancient Romans believed that coral had the functions of preventing disasters, giving people wisdom, stopping bleeding and driving away heat. Closely related to Buddhism. Buddhists in India, China and Tibet regard red coral as the incarnation of Tathagata. They regard it as a mascot for offering sacrifices to the Buddha, and it is often used to make beads or decorate statues. This is a very precious jewel. Echinozoa of the class Polypodiaceae. Characterized by calcareous, horny or leathery endoskeleton or exoskeleton. The word coral also refers to the bones of these animals, especially calcareous ones. There are about 1 1,000 species of stony corals (1230:Madreporaria or Scleractinia); There are about 100 species of black coral and spiny coral (antipatharia); There are about 1, 200 species of [〔Gorgonacea〕] (or horny corals); There is only one kind of blue coral (Coenothecalia). Coral is just a hydra-shaped individual, hollow and cylindrical, with the lower end attached to the surface of the object and a mouth surrounded by one or more tentacles at the top. Tentacles are used to collect food and can be stretched to a certain extent. It has specialized cells (stinging cells). When the stinging cells are stimulated, they will turn out the stinging silk sac and paralyze their prey with stinging silk. Eggs and sperm are produced by gonads on the diaphragm and discharged into seawater through the mouth. Fertilization usually occurs in seawater and sometimes in the gastric circulation cavity. Usually fertilization only occurs between eggs and sperm of different individuals. The fertilized egg develops into a floating larva, which is covered with cilia and can swim. After a few days to weeks, it will be fixed on the solid surface and develop into a hydra. It can also be propagated by budding, which will not be separated from the original hydra after budding. New buds keep forming and growing, so they breed into groups. When the new hydra grows and develops, the old hydra under it dies, but the skeleton remains in the population. Soft corals, gorgonian corals and blue corals live in groups. Each hydra in the population has eight tentacles, and there are eight diaphragms in the gastric circulation cavity, of which six diaphragms have cilia for introducing water into the gastric circulation cavity, and the other two diaphragms have cilia for guiding water out of the gastric circulation cavity. Bones are endoskeletons. Soft coral is widely distributed, and its skeleton is composed of calcium-containing spicules separated from each other. Some species are disc-shaped, and some species have finger-like protrusions (such as species of genus [〔Alcyonium〕], commonly known as dead fingers). Horny corals are abundant in tropical shallow waters, and they are banded or branched in shape, and the length can reach 3 meters (10 foot). Horny corals, including so-called expensive corals (also known as red corals and rose corals) can be used as decorations, among which the common species is Mediterranean red corals. The blue coral (Heliopora coerula) is found on the coral reefs formed by middle-stone corals in the Indian Ocean and the Pacific Ocean, forming a block with a diameter of 2 meters. Rock coral is the most well-known and widely distributed species, living alone or in groups. Like black coral and spiny coral, the number of septa is 6 or multiple of 6, and the tentacles are simple and have no feathers. Stone coral, black coral and spiny coral are different from related anemones mainly because of their exoskeletons. Rock corals can be found in all oceans from the tidal zone to the depth of 6000 meters (about 20000 feet). For species living in groups, the diameter of hydra is 1? 30 mm (0.04? 1.2 inch). Most living stone corals are light yellow, light brown or olive, depending on the algae living on the coral. But its bones are always white. The largest stone coral living in a single cell is an animal of Fungia with a diameter of about 25 cm (10 inch). The skeleton of stone coral is cup-shaped, wrapped with hydra, and its composition is almost pure calcium carbonate. Its growth rate depends on age, food supply, water temperature and species. Ring coral islands and coral reefs are formed by the bones of stone corals, and their formation rate is about 0.5 per year on average. 2.8 centimeters. The common stone coral species are nautilus coral, mushroom coral, star coral, staghorn coral and so on, all of which are named after their shapes. Black coral and spiny coral are whip-shaped, feather-shaped, tree-shaped or bottle-brush-shaped, and distributed in the coastal waters of the Mediterranean Sea, the West Indies and Panama. Due to environmental pollution, a component that makes corals easy to die in the air has appeared in some coral areas, so the species and quantity of corals in the world have decreased sharply.