What is coral?

Corals are sessile animals, belonging to Phylum Cnidaria which also includes an enormous range of jellyfish, hydroids, soft corals, anemones and many others.

Each coral colony is made up of many individual coral animals, called polyps. Each polyp is essentially a hollow cylinder, closed at the base and interconnected to its neighbours by the gut cavity. The polyps have one or more rings of tentacles surrounding a central mouth.

We usually classify corals into stony corals, octocorals and hydrocorals, each type with different morphological characteristics and highly variable forms.

Stony Coral

Hydrocoral

Other than taxonomic classification, corals can be divided into two ecological groups. Corals that contain symbiotic algae, zooxanthellae, are referred to as hermatypic or reef-building corals, while those that do not are called ahermatypic or non-reef-building corals.