Actiniaria – Sea Anemones
The Sea Anemones are an order of the Anthozoa with about 1200 known species. Actiniaria are very colourful and even within some styles there are fancy colour variations.
The body of a Sea Anemones consists of a foot disc, the body and an oral disc. The latter consists of the mouth and tentacles. A skeleton is not present with them. Contrary to many other orders, their body is very muscular.
The size of different species varies greatly. It ranges from a few millimetres up to a diameter of 1.5m.
Actiniaria can be very colourful but also of one colour. Sometimes colour variations occur within a species.
Distribution and Habitat
Sea Anemones live predominantly benthic, on a solid ground. Some species also prefer sandy soils or live pelagic.
Actiniaria live exclusively in salt water, meaing seas and oceans. Their distribution ranges from the Arctic to the tropical regions. However, the greater part of them lives in warmer areas.
Sea Anemones live solitary and are semi sessile. That means, they can move slowly, creeping on their feet. I was able to observe this only at the Berried Anemone. So if a location does not offer enough light, food or water movement, they simply go for a new one.
Actiniaria feed on small fish, crustaceans, snails or plankton. Some of them also live in a symbiosis with zooxanthellae and are therefore supplied with various nutrients. There are symbioses with different crustaceans. For example, very often Sexy Shrimps are found together with Club Tipped Anemones. Nemo, the anemone fish, is also a good example of such a living together.
Reproduction and Development
There are very different reproductive methods among the different species of Sea Anemones. Some release eggs that are then fertilized. In addition, there is hermaphroditic, single-sexed and asexual reproduction.
In particular, the free swimming medusa phase does not take place. From the fertilized eggs planula larva develop. These look for a certain location where they develop into a new polyp.