Clownfish live among stinging anemones, protected by a mucus layer that keeps them safe.

The longer version

A slimy coating keeps neighbouring stinging cells from firing, either by masking the surface or by lacking whatever cue triggers them. First contact is cautious: the newcomer brushes tentacles repeatedly until the reaction stops, building up tolerance before settling permanently.

The arrangement suits both sides. The anemone gains cleaning, better circulation from fluttering fins, and defence against its own predators, while the fish gets shelter that almost nothing else dares enter. It rarely strays far, since protection ends at the tentacle tips. Some pairings are exclusive, whereas others tolerate several hosts. Tropical reef communities host dozens of such partnerships between anemones and resident fish.

Where this entry sits

Oceans and Sea Life looks at the salt water that covers most of the planet, from crashing waves and tides to the darkest deep-sea trenches. Expect notes on coral, fish, whales, sharks, jellyfish, shells, and the strange creatures that live far below the surface. The full list sits on the Oceans and Sea Life page, where every entry is listed in order.