The anemones are animals belonging to the phylum Cnidaria. This phylum includes free-living animals (such as jellyfish) and sessile (immobile) animals (such as anemones). Anemones can move (very slowly and for very short distances), but are predominantly sessile animals. They have a simple structure and live in aquatic environment – most of them are marine, although there are some fresh water species. They are widely distributed: we can find species living in temperate climates and others that occur in tropical climates. They can reproduce sexually or asexually.
They have a polyp-shaped body (sac or tube), with a cavity in the interior (the gastro-vascular cavity), a basal disc in the lower part and tentacles in the upper part. The basal disc is responsible for fixing the anemones to the substrates (usually rocks) and also for their slow locomotion. The gastro-vascular cavity communicates with the outside through a single opening that functions as mouth and anus and around which there are tentacles. In the tentacles we can find the cnidocytes, special cells working as a defense structure, also used to capture food. The colors and movement of the tentacles attract animals (like small fish) that, when approaching the anemone, undergo the action of the cnidocytes – these produce and release a substance that paralyzes the animals, facilitating their capture by the anemone. The prey are then brought to the mouth, from where they move into the gastro-vascular cavity, where they are digested.
In order to overcome the obstacle that is their immobile nature and try to capture more food, anemones can attach to animals (usually animals with a shell) rather than to remain attached to rocks. Both end up benefiting from this association: the anemone is transported by the animal to which it is attached, and thus can capture food in other places, and, in return, gives it a certain protection – in addition to working as a kind of camouflage, its tentacles with stinging cells may also ward off predators.
A very particular relation is established between the anemones and the clownfish. These fish produce a substance that covers their body and gives them immunity against the paralyzing action of the cnidocytes. Clownfish can thus live between the tentacles of the anemone, protected from potential predators that do not approach the anemone to prevent the attack of the cnidocytes. The clownfish also lay their eggs on the rocks, next to the anemones, so that they are also protected. On the other hand, the anemone takes advantage of the food leftovers of the clownfish or even captures some animals that eventually approach looking for the clownfish.
The cnidocytes can also be harmful to man, causing a reaction on the skin. It is therefore advisable to try to avoid touching the tentacles of the anemones.
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