Sea anemones belong to the cnidarian group of invertebrates, which also includes jellyfish and coral polyps. Looking like flowers, their bodies consist of a sticky foot ("pedal disc"), a column-like body and a set of stinging tentacles grouped around a central mouth. The tentacles are used both to paralyse and capture prey, and to fend off enemies. Although they generally stay in one place, sea anemones can move if conditions become unfavourable to them. They can creep slowly about on their foot, or by swimming, either by flexing their bodies or using their tentacles.

Tentacles

Sea anemones anchor themselves to rocks with their stinging tentacles pointing upwards. The tentacles are used to catch zooplankton and shrimps (larger species can prey on fish), paralyse them and draw them into the anemone's mouth. The tentacles are lined with hairs. When a hair is touched, it shoots out a tiny venomous "harpoon", called a nematocyst, which attaches itself to the animal that triggered it.

Clownfish

The clownfish lives inside the poisonous tentacles of sea anemones. The fish is protected from the poison by a layer of mucus on its body, but its enemies would be stung to death by the anemones. In return for its protection, the fish keeps the anemone clean. The anemone also feeds on the scraps left over from the clownfish’s meals.