Let's start with an animal that looks as if it's glued to the surface, the beadlet anemone (Actinia equina). The anemone looks like a small lifeless blob of red, brown, green or orange jelly most of the time. It's hard to see even it's tentacles, especially during the daytime. But is it really as inactive as it seems? Not at all. The anemone is actually very aggressive and if your aquarium animals are unfortunate enough to get it for a neighbour, it might happen you'll end up with only one animal - the anemone. Even the clown fish, which are used to anemone toxins are not safe.
How can this non mobile tomato catch anything but unsuspecting go-byers you might ask? Well, the beadlet anemones are actually mobile and they will often move, stinging and eating neighbouring anemones. And other creatures that can’t escape.
Out of water, the anemone retracts its fearsome tentacles into gastrovascular cavity. It helps it to conserve water while being out of the water or even covered by sand. It also covers its body with mucus which gives it a shiny look.
When the tide comes, it’s time to eat. The anemone displays up to 192 tentacles, arranged in six circles. The unsuspecting pray comes by and the anemone senses its presence. The attack is on and the stinging cells (nematocysts) fire. When they release toxins into the prey they paralyze the organism, inhibiting its ability to escape. And the dinner is served.
Beadlet anemone will eat anything it can catch. Its diet includes clams, isopods, snails, bryozoans , and chitons.
Despite its stinging cells, Actinia has predators on her own. When they come, it usually decides among three strategies: it inflates its body column to reduce damaged areas, detaches itself off the substrate and tries to escape, or releases the stinging cells containing toxins. The grey sea slug, Aeolidia papillosa, doesn't care though. It somehow does not digest the most toxic stinging cells so they don't bother it.
When another bead anemone comes to claim new territory, it's another story. The battle is on. The competitors use acrorhagi (bright blue spots located just beneath the tentacles, organised as an external ring) containing stinging cells to fight over territory. The skin flies off, stinging cells are being fired. Finally, one has to quit and the proud owner of a new territory claims its new position. The looser doesn't have to go very far, just out of the reach of the winner's tentacles.
In the time of reproduction, the male excretes sperm which goes into the gastrovascular cavity of the female, where the egg is fertilised. The beadlet anemone is the only species of anemones to brood its young. So the larva develops inside the cavity and only then crawls out of its parent to begin its short period of planktonic life. After that, it enters the cavity of another sea anemone (male or female) and develops further. Once the anemone is ready to be "born", the "parent" anemone catapults it through the water. When it lands, it secures itself on some solid, solitary substrate and begins its life as a small tomato.
Interesting facts
- Actinia equina can move half a meter in a day.
- Although its poison is detrimental for the prey, it is not dangerous for humans.
- It can be found on rocky shores of the United Kingdom, Western Europe and the Mediterranean as well as the Atlantic coast of Africa.
More facts on Wikipedia and Animal Diversity Web.
