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What is a Sea Anemone?

Victoria Jordan
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.

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.

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

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.

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

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.

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.

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.

Frequently Asked Questions

What exactly is a sea anemone?

A sea anemone is a marine invertebrate belonging to the phylum Cnidaria, which also includes jellyfish and corals. They are known for their colorful, flower-like appearance and their symbiotic relationship with clownfish. Anemones anchor themselves to rocks or coral using an adhesive foot, called a basal disc, and capture prey with their venomous tentacles.

How do sea anemones feed and what is their diet?

Sea anemones are carnivorous, feeding on small fish and invertebrates that get caught in their tentacles. They use specialized cells called cnidocytes to inject venom into their prey, which immobilizes it. The prey is then moved to the mouth by the tentacles. Anemones can also absorb nutrients from symbiotic algae living in their tissues.

Can sea anemones move?

While often stationary, sea anemones can move in several ways. They can glide slowly on their basal disc, detach and drift to a new location, or swim by flexing their body. However, these movements are not rapid, and anemones typically remain in one place for extended periods, especially if food is abundant.

Are sea anemones dangerous to humans?

Most sea anemones pose no threat to humans, as their venom is not potent enough to cause serious harm. However, some species, like the Hell's Fire anemone, can deliver a painful sting that may cause allergic reactions or skin irritation. It's always best to admire anemones from a distance and avoid touching them.

What is the lifespan of a sea anemone?

Sea anemones can have remarkably long lifespans, with some species living for decades or even surpassing a century. According to scientific studies, the lifespan of an anemone can vary greatly depending on the species, environmental conditions, and threats from predators or human activities.

How do sea anemones reproduce?

Sea anemones have versatile reproductive strategies. They can reproduce asexually by budding, fission, or pedal laceration, where small pieces of the base develop into new individuals. Alternatively, they can reproduce sexually by releasing sperm and eggs into the water, where fertilization occurs, leading to the development of free-swimming larvae that settle and grow into new anemones.

Discussion Comments

PelesTears

@ 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.

Georgesplane

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.

istria

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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    • Sea anemones use their tentacles to reel in prey.
      By: Fraser Lloyd
      Sea anemones use their tentacles to reel in prey.
    • Some sea anemones attach themselves to hermit crab shells.
      By: haveseen
      Some sea anemones attach themselves to hermit crab shells.
    • 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.