Although many people mistake corals and anemones as plants, they are actually animals called Anthozoa, which in turn belong to a larger group of animals called cnidarians that carry a sting in their tentacles.
The basic unit of the adult is the polyp; this consists of a cylindrical column topped by a disc with a central mouth surrounded by tentacles.
Colonies of coral polyps are formed by the budding of new polyps from an original, founding individual to create extensive coral reefs.
There are many hundreds of different coral species living in the shallow waters around all of the Koh Lanta dive sites, creating extensive coral reefs and sanctuaries for millions of reef fish.
Anthozoans are carnivores, catching prey with their tentacles. Many species supplement their energy needs by making use of photosynthetic single-celled algae that live within their tissues.
The two main subclasses of Anthozoa are the Hexacorallia (6 sided) and includes the 837 known species of living stony corals, sea anemones, tube anemones and zoanthids. Octocorallia (8 sided) include the soft corals and gorgonians (sea pens, sea fans and sea whips), and sea pansies.
The family of honeycomb corals, Diploastreidae contains only a single genus, Diploastrea, which in turn has only a single member species, Diploastrea heliopora.
Mushroom corals of the family Fungiidae are flat or dome-shaped, with round or oval skeletons and a possible central arch. These corals are mostly solitarily and free-living (they are not attached to the substrate). Most mushroom corals are in fact a single, giant polyp, some with multiple mouths. A few species do actually form small 'colonies' in that several polyps live within the same, shared skeleton.
The family Acroporidae are known as 'staghorn' or 'branching' corals. Staghorn corals come in many shapes and sizes and can be highly variable in colour and form, even within the same species. Colours and colony formation can depend on the growing conditions of the coral, depth, clarity of water, currents, and so on.
Merulinidae are a family of stony corals which create large colonies and are reef-building corals. Members of this family are common around Koh Lanta and have a wide range of colony shapes. Corallites are often directly next to each other, packed tightly, sharing coralite walls and are often highly fused.
There are several species of Bubble Corals found in the Indo-Pacific area, some of which we can find here on the dive sites around Koh Lanta. Bubble Corals can be mistaken for soft corals, however they have a hard, stony skeleton just below the surface.
Like the other soft corals, Ellisellidae is a family of whip corals which do not produce calcium carbonate skeletons. Instead, these corals have flexible skeletons made from a complex protein called gorgonin.
Subergorgiidae Giant Fans
The six species in this family have strengthened their inner skeletons with gorgonin to such an extent that they are far less brittle than other related soft corals.
Members of this family are bushy to tree-like and can be found in calm waters exposed to strong currents (but not to strong waves). Soft corals of this family are found everywhere, but particularly in abundance at Hin Muang and Hin Daeng and around deeper areas at Koh Haa. Sometimes known as 'tree corals'.
Sea Anemones are a group of predatory invertebrates classified in the phylum Cnidaria. They get their name from the vibrant terrestrial flower, the Anemone. There are more than 1,000 species found around the world's oceans at various depths, the largest and most varied occur in coastal tropical waters.