Coral Field Guide
What is the distribution of Coral Communities in Hong Kong? What are Corals? Corals are animals belonging to Phylum Cnidaria, a group of animals that include hydroids, jellyfish and sea anemone. The word "coral" has been used to describe different organisms in this group, including the black coral, sea fan, soft coral and hard corals.
Soft corals and sea fan belong to the former group. They are also characterized by the absence of external calcareous skeleton (exoskeleton). For soft corals, their skeletons are in the form of needle-like structures called sclerites found inside their body. Sea fans also have this type of endoskeleton, but in addition, they also have axial skeleton mainly made up of proteinaceous horny materials that form the core of their branching colonies. Hard corals belong to the group Hexacorallia, together with black corals. Hard corals have calcareous exoskeleton but do not have endoskeleton. Black corals have axial skeleton that is also organic in nature. Hard corals grow progressively by depositing more and more calcareous materials underneath their living tissues. So a living hard coral colony is made up of layers of dead skeleton materials (mainly calcium carbonate) with a thin veneer of soft tissue on top. It is these hard corals that build up the foundation of the coral reef with the calcium carbonate deposit over thousands and thousands of years.
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