Giant green anemone
A bright green tide-pool anemone that farms algae inside its own body for the color and eats crabs whole with a ring of stinging tentacles.
Giant green anemone at a glance
Anthopleura xanthogrammica JY-unt green uh-NEM-uh-nee; Anthopleura xanthogrammica is an-tho-PLOOR-uh zan-tho-GRAM-ih-kuh
- Type
- Invertebrate · sea anemone
- Diet
- Carnivore
- Size
- About the width of a coffee-cup saucer across the tentacles, up to roughly 7 inches.
- Lifespan
- Not known exactly, but relatives in this group can live many decades and possibly far longer.
- Conservation
- Not formally assessed by IUCN; common along the Pacific coast
Eats crabs, mussels, small fish, sea urchins
It waits with its ring of tentacles open. When prey brushes them, thousands of tiny stinging cells fire like harpoons, the tentacles fold the stunned animal into the center, and the whole thing is swallowed into the stomach and digested.
Should you worry?
Its sting is far too weak to hurt a person, though it feels sticky if you touch a tentacle. The real rule is for the animal, not you. A poke or a dry hand can harm it, so look and leave it be.
A saucer-sized blob of jelly-green sits open in an Olympic tide pool, a ring of tentacles swaying in the current, glowing a green so bright it seems lit from inside. It only looks like a plant. The color comes from millions of tiny algae living in the anemone’s own flesh, catching sunlight and making food they share with their host. An anemone that grows in a dark sea cave, where the algae can’t work, comes out pale and gray instead. The green is a garden the animal keeps under its own skin.
The tentacles are not decoration. Each one is loaded with thousands of microscopic capsules that fire like harpoons the instant something brushes past, spearing and stunning it. A crab wanders too close, the tentacles fold it inward toward the mouth at the center, and the anemone swallows it whole into the hollow of its body to digest it there. Mussels, small fish, even sea urchins go the same way.
Come back to the same pool at low tide and you might not find it at all. With the water gone, the anemone pulls every tentacle inside and clamps down into a squat green blob, holding a mouthful of seawater to keep from drying in the sun. It can sit like that for hours, closed and patient, a garden and a mouth folded shut, waiting for the tide to come back and open it again.
Did you know?
- Its brilliant green comes from tiny algae living inside its tissue, not from the animal itself. Individuals in dark caves with no sunlight for the algae turn pale and colorless.
- It stuns prey with thousands of microscopic stinging harpoons called nematocysts, then swallows animals as big as a crab whole.
- It can pull its tentacles all the way inside and clamp shut into a blob when the tide goes out, holding water in to keep from drying while it waits for the sea to return.
Common questions
Why is the giant green anemone so green?
Because of tiny algae that live inside its body and make food from sunlight. The algae give it the green color, and anemones growing in dark places without sunlight turn pale instead.
Does a green anemone sting?
Yes, but its sting is far too weak to hurt a person. It uses thousands of microscopic stinging cells to catch crabs and small fish, not to bother swimmers.
What happens to an anemone when the tide goes out?
It pulls its tentacles inside and closes up into a squishy blob, holding seawater in so it doesn't dry out while it waits for the tide to come back.