Suddenly, while swimming underwater, you may encounter a large flower with soft “arms” that can catch prey and swallow it whole. Upon closer inspection, you will notice that this flower rarely moves because it moves very slowly. This is a species of animal known as “sea anemone” belonging to the order Actiniaria. They have colorful tentacles, making them resemble flowers from the outside. There are over 1,000 relatives of sea anemones, with body diameters ranging from a few millimeters to 1.5 meters.
At the tips of the tentacles are stinging cells that can adhere to surfaces. This adhesive ability is due to many stinging cells with very fine needles. The tentacles shoot tiny spikes into whatever they need to attach to. In addition to adhesion, the tentacles are also used effectively by sea anemones to sting, paralyze, or kill their prey. Muscles help the sea anemone gradually pull the prey towards its mouth. After that, the muscles slowly draw the prey into its stomach.
The body structure of the sea anemone is quite unusual: almost the entire body is occupied by a large stomach. The short throat is located just above the stomach and directly below a mouth. The mouth is centered in a disc-like structure surrounded by rows of tentacles. Sea anemones do not have (and do not need) a brain, heart, kidneys, lungs, or a sturdy skeleton. They contract muscles to squeeze the water-filled stomach, making it look like a water balloon.
When the tide recedes and exposes the sea anemone, they will strongly contract their muscles and retract their tentacles into their bodies. They also know how to camouflage by using adhesive pads on the upper part of their bodies to cling to rocks and shells around them while curling their bodies.
Sea anemones can live both in and out of water. This creature has remarkable adaptability. They can be found at depths of over 10,000 meters; some even survive in brackish waters.
Although they occasionally kill and eat crustaceans, sea anemones also allow “friend” crabs to make their “homes” among their dangerous tentacles.