Types of corals

Acropora staghorn coral Photo: Vicki Harriott

• Hard (stony) corals (Order = Scleractinia) have six (or a multiple of six) tentacles on their polyps. They have an internal limestone skeleton.
• Soft corals (Order = Alcyonacea) have eight tentacles on their polyps. They are soft or leathery in texture and have limestone sclerites instead of a solid sketelon). Soft corals are closely related to gorgonians (sea fans)

Both hard and soft corals can be further divided into different groups (families, then genera) that have shared features.

Hard corals can also be divided into:

• Hermatypic corals, which contain plant cells (zooxanthellae) (How do corals grow?), so are usually able to produce large amounts of limestone for building reefs and:
• Ahermatypic corals, which do not have plant cells. These corals are not reliant on light so are often found in caves or deep water, but they are generally not able to contribute as much to building reefs as hermatypic corals.

Common names for corals refer to their colony shape. These include massive, staghorn or branching, plating, encrusting, columnar, corymbose and foliacious (leaf or vase-like).

Favia Photo: Vicki Harriott	Goniopora Photo: Vicki Harriott	Hydnophora Photo: Vicki Harriott	Echinophyllia Photo: Vicki Harriott	Tubinaria vase coral Photo: Vicki Harriott