Animalia Life

Coral refers to a large group of marine invertebrates, class Anthozoa, in the phylum Coelenterata. Anthozoa form reefs, gorgeous coral bushes, and precious coral, used for jewelry. The individual organisms involved are coral polyps. They have protective calcium carbonate (limestone) or horn skeletons. Stony corals of the order Scleractinia, also called true corals, form reefs. The reefs are limestone formations in oceans, made by billions of polyps. The polyps have saclike shapes, with a mouth at the upper end, surrounded by tentacles. Coral polyps form reefs from calcium taken from ocean water and deposited around their bodies. Besides reef-building corals, their relatives, gorgonians, have skeletons of flexible, horny material. Gorgonians make coral bushes and lacylooking coral fans. These formations are covered with live polyps, which are yellow, pink, purple, brown, and even black. Wherever they occur, such as inWest Indian waters, the forms produced look like parts of underwater gardens. Precious coral is used to make jewelry. It is produced by polyps closely related to gorgonians. This hard coral polishes into beautiful red, rose, or pink material that can be made into jewelry beads. Most precious coral grows as small "bushes" in the Sea of Japan and the Mediterranean.

Physical Characteristics of Coral Polyps
There are two colonial anthazoan subclasses, differing in radial symmetry. The first, Octocorallia, is composed of eight-tentacled animals. Included are gorgonians and red precious coral. Members of the second subclass, Hexacorallia, have six tentacles (or multiples of six tentacles). Hexacorallia include true corals (Scleractinia). Most scleractinians are colonial. Their polyps have diameters of about 0.1 inches and are interconnected. The shapes of coral colonies, such as branched forms, depend on the coral species. Colonial corals can grow in deep waters, but reefbuilding corals occur only in warm, shallow ocean regions. The true corals secrete calcium carbonate from the bottom of each polyp, forming skeleton cups in which each polyp is anchored and into which it withdraws for safety. In an oral apparatus atop the stalk is an opening with tentacles and cilia. It serves as both mouth and anus. At night, the tentacles catch plankton and carry them to the mouth. Stinging cells on the tentacles paralyze prey.

Life Cycles of Coral Polyps
Each coral colony grows by asexual polyp budding. Live polyps build on limestone or horn de- posits of past generations. In this way, they make new reefs or other coral masses. The polyps remain associated in colonies. The combined limestone- or horn-forming activity of a colony yields huge masses of coral. They may be dome-shaped or towering and branched. Live polyps cover the outside of each mass and create its gorgeous colors, ranging among tans, browns, oranges, yellows, pinks, purples, and greens. When reef coral is removed from the ocean, the polyps die and wash off, leaving behind white skeletons. These corals build foundations for tropical atolls and barrier reefs. Reef corals must live at depths where light penetrates, because symbiont algae (zooxanthellae) that live in their tissues require sun light for photosynthesis, and polyps cannot exist without the algae. The algae produce most of the carbon compounds that polyps use to make energy and protoplasm. The plankton caught by polyps provides the algae with nitrogen, phosphorus, and other nutrients otherwise unavailable. The coral's dependence on the algae varies with coral species and habitat.

Coral Reefs and Atolls
Coral reefs, elevated parts of shallow ocean floors, form by accumulation of calcium-containing exoskeletons of scleractinian polyps. The tropical reefs extend to 30 degrees north and south of the equator. They form only in shallow waters, at temperatures of 65 degrees Fahrenheit or warmer. The three reef types are fringing reefs, barrier reefs, and atolls. Fringing reefs extend from the shore, with no body of water between reef and land. Barrier reefs are farther offshore, follow shorelines, and are separated from them by lagoons. They form barriers between the shore and the open ocean. Atolls are coral islands that have narrow, horse-shoe reefs and shallow lagoons. Many South Pacific islands are atolls. Reefs are especially abundant on the east coast of the Americas from Brazil to the West Indies, along Florida's coast, and through the Bahamas and Bermuda. Very beautiful reefs occur in the South Pacific islands, the East Indies, and near Madagascar. The most magnificent coral reef is the Great Barrier Reef of Australia, over 1,200 miles long. Polyps that build reefs have diameters from 0.05 inches to 1 foot. Constant battering by the ocean breaks up the reefs. The pieces accumulate over time, and eventually reach above the ocean surface. Soil deposited by ocean water lodges on them, and seeds wash up and become vegetation. Then the pile of coral debris becomes a coral island or atoll.

Coral Facts

Classification:
Kingdom: Animalia
Phylum: Coelenterata
Class: Anthozoa
Subclass: Hexacorallia (six-tentacled or six-tentacle multiples), Octocorallia (eight-tentacled)
Orders: Include Gorgonia (bush or fan corals), Scleractinia (true corals, Hexacorallia)
Geographical location: Mediterranean, Sea of Japan; east coast of the Americas from Brazil, through the West Indies, and along Florida coast; the Bahamas and Bermuda; South Pacific islands; East Indies; Indian Ocean; around Australia
Habitat: Marine, warm to tropical waters
Gestational period: None; reproduction uses asexual budding of indeterminate duration
Life span: Coral colonies can live indefinitely as living polyps grow on the skeletons of dead ones
Special anatomy: Tentacles, exoskeletons

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