Hard coral

Definition
noun, plural: hard corals
Any of the coral species that build coral reefs by their deposition of calcium carbonate when they create a stony skeleton
Supplement
Corals are invertebrate species. They belong to the class Anthozoa of phylum Cnidaria. Corals may be hard corals or soft corals. Hard corals form a colony and serve as a primary component of a coral reef. A coral reef consists of hundreds or thousands of coral polyps that are connected to each other. The coral polyps secrete calcium carbonate deposits to form a hard skeleton. This deposit renders the corals protective and structural support to the colony. The coral reefs are an important marine structure because they provide an underwater ecosystem for various small marine animals. Some of them are in ecological partnership with zooxanthellae, which are dinoflagellate endosymbionts and are sometimes responsible for the coloration of the reef.
Examples of coral species that are considered as hard corals are brain corals and elkhorn corals. Many of the hard corals belong to the order Scleractinia.
Soft corals do not produce coral reefs and lack the hard skeletons. They also form symbiosis with zooxanthellae but may readily feed on zooplankton.
Scientific classification:

• Kingdom: Animalia
• Phylum: Cnidaria
• Class: Anthozoa
• Subclass: Hexacorallia
• Order: Scleractinia Bourne, 1900

Synonym(s):

reef-building coral

See also:

• coral
• soft coral