TINY DANCER

The immortal freshwater organism that tangles prey with its toxic, harpoon-flinging tentacles

- Nick Baker

GREEN HYDRA

IN GREEK MYTHOLOGY THE HYDRA WAS a poisonous, many-headed serpent with frustratingly effective powers of regeneration - cut off one of its heads and two would grow in its place. A monster of myth, right? Well, actually, no. Hydras do exist. You can find them in your local pond and they're as terrifying as the mythological one, just a bit smaller.

The green hydra (Hydra viridissima) is the only one of our four native species that's green. It's also less than 10mm long, so the only things it'll be terrorising are water fleas and small fish fry.

Think of them as skinny sea anemones. They're part of the Cnidaria group of animals, which also includes jellyfish and corals. They're quite simple creatures, little more than a flexible tube with a mouth at one end, surrounded by a crown of tentacles. They have no heart, brain, eyes, or gills. But don't let the simplicity of this particular cnidarian fool you: hydras are fascinating creatures.