The Octocorallia are a subclass of the Anthozoa, which contain about 3200 species. Octocorallia are also often referred to as Alcyonaria.
Apart from the genus Talaroa, all Octocorallia live in colonies. Depending on the species, the colonies can colonize areas or grow mushroom, shrub, tree and fan-shaped. Some reach a diameter of one meter and grow several meters in height.
If present, they always have eight feathered tentacles. The gastric space (stomach) is also divided into eight chambers.
Most of theOctocorallia do not have a solid limestone skeleton, but have only small limestone needles.
Distribution and Habitat
The Octorocallia usually live on solid ground. They occur from shallow water to more than 4000 m depth. Sea pens are an exception here, because they inhabit sandy or muddy soils.
They occur all over the world, in all seas. Although they are increasingly found in tropical zones, they can be seen up to the Arctic. In this way, rocky reefs, caves and steep walls are settled.
Octocorallia predominantly live in colonies and sessile. This means they do not change their location.
Their diet consists of plankton that they mainly catch at night with their feathered tentacles. Studies have shown that it is almost exclusively phytoplankton, which consists only of plants. This also results in the yellow, red or orange colouration of the individual species. This is caused by carotenoids, which are produced only by phytoplankton.
In addition, Octocorallia are often oriented transversely to the current in order to absorb more food.
Species from the tropical regions live with Zooxanthellae in symbiosis and thus cover a large part of their nutrient requirements.
In order to protect oneself from enemies, Octocorallia produce toxic or disgusting substances. In the same way, the struggle for space is also conducted. Thus, species of the Octocorallia can emit substances that cause the stony corals to eject their Zooxanthellae. This causes them to fade.
Octocorallia can reproduced sexually or asexually. There are hermaphroditic and separate sexes. There are also two different types of sexual reproduction.
On the one hand, there are Octocorallia, which simply deliver sperm and egg cells into the water, where the eggs are then fertilized. This takes place at certain moon phases or temperatures, so that the chances of fertilization are increased.
On the other hand there are so-called breeders. Only the sperm are released into the water. The ova remain in the polyps, where they are fertilized by the spermatozoa. When the larvae are ready for metamorphosis they are ejected. This can happen days or weeks later.
A way of asexual reproduction resembles the cuttings in plants. Broken parts of colonies are able to regrow in a different place.
They represent more than a third of the living reef cover.
Nearly a third of all Cnidaria are among the Octocorallia.
Since they do not have a stable skeleton, they are not involved in the construction of coral reefs, with a few exceptions.