What is a Sea Anemone?

Victoria Jordan

A sea anemone (order Actiniaria) usually resembles a flower with a crown of tentacles surrounding a disk on top of a column-like body. They can retract these tentacles completely, appearing as if they are no more than a harmless blob.

Sea anemones use their tentacles to reel in prey.
Sea anemones use their tentacles to reel in prey.

The tentacles have stinging cells called nematocysts that are used to immobilize or kill their prey, which can be anything from tiny plankton to fish much larger than itself. The sea anemone pulls its victim into its central body cavity, which is almost entirely made of a giant digestive gland. When the anemone is antagonized, some species produce special stingers called acontia (singular: acontium) through the pores in its column.

Some sea anemones attach themselves to hermit crab shells.
Some sea anemones attach themselves to hermit crab shells.

It may look like sea anemones are immobile, rooted in place like a plant, but this is only an act, part of their disguise. They can actually glide slowly along the ocean floor using their muscular base. Crafty hunters, sea anemones are excellent at appearing as if they are just a part of the flora and fauna of the sea in order to avoid attackers and fool their prey.

Varying in size, a sea anemone can be anywhere from a couple of inches wide (5cm) up to three feet (1 meter) across in some tropical species (Stoichactis). They live very long lives; some have been known to survive almost a hundred years. A sea anemone can reproduce sexually or by budding a new family member from the base of their column.

Some sea anemones have been found at some of the ocean's deepest spots. The deepest is noted at about 30,000 feet (9,000 meters). Most sea anemones, however, live in tide pools or tropical coral reefs. The large tropical species, are often so colorful with tentacles that range from pink to yellow to red, that they blend in with the other inhabitants of active tide pool communities.

Sea anemones often develop symbiotic relationships with other sea creatures. The most famous is the clownfish (Amphiprion) who lives within the protective tentacles of the sea anemone, immune to its poison, and feeds on the crumbs of its host anemone's meals.

Some sea anemones live affixed to the shells occupied by hermit crabs (Eupagurus). When the crab moves out, the only thing that comes with them is their anemone friend.

The clownfish is immune to sea anemone poison and feeds on the crumbs of its host anemone's meals.
The clownfish is immune to sea anemone poison and feeds on the crumbs of its host anemone's meals.

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Discussion Comments


@ Georgesplane- I would love to take a trip to a tropical island to scuba dive at a reef. I have seen sea anemone at an aquarium, but to be underwater and see all those creatures in their own element must be amazing.


I went to Maui for my wedding. I went on a dive with my fiancée at Black Rock off the Ka’anapali Coast. We are beginners so it was an easy shore dive, but it was one of the most amazing experiences ever. We saw a green sea turtle, parrotfish, puffer fish, a shark, an octopus gliding across the coral, and even a small shark.

One of the coolest things that I saw though was a small sea anemone that had a shrimp living inside. At first, I thought that the sea anemone was eating the shrimp, but after we went topside, our guide told us that shrimp and sea anemone share a symbiotic relationship. I was fascinated that such a toxic creature would house and protect such a small colorful shrimp.


What a great article. I never knew that the hermit crab and sea anemone shared the same real estate.

I believe that the true final frontier is the oceans of the planet. I was surfing the NOAA website and I came across an interesting piece of information. Man has only explored 5% of this planet’s oceans. Our species has climbed the planets highest peaks, infiltrated the deepest rain forests, and even set foot on the moon, but we still have not found a way to conquer the oceans. This is awe inspiring to me. I grew up surrounded by oceans, and every time I dove into the water, I felt fear and excitement. Once again great article wiseGEEK...I learn something new every time I visit this site.

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