This unpronounceable undersea animal has some surprising features, as Paul Naylor reveals
Some of the miniature "harpoons" shot out by anemones have blades which unfold and, coupled with the twisting motion of the thread, act like drills to penetrate the body armour of small crustaceans. Some also inject poison to paralyse prey. Sea anemone stings do not hurt humans, unlike those from some of their relatives, the jellyfish.
Some species of anemone live on the shells of hermit crabs, gaining transport and extra food in the form of the crab's leftovers. The crab gains protection, courtesy of anemone's stinging cells. One type of anemone even builds an extension to the hermit's home, freeing it from the need to move frequently.
More than 30 species of sea anemone are found in UK waters, ranging from those with fine feathery tentacles (such as plumose anemones) which catch only small prey such as plankton, to those with stronger tentacles (such as the dahlia) which prey on larger creatures, including prawns and fish. The photograph shows dahlia anemones.
Sea anemones might look like undersea flowers, but they are well-equipped predatory animals. Their tentacles are armed with batteries of thousands of stinging cells which are used for entrapping and immobilising prey, as well as for defence. When triggered, these stinging cells shoot out tiny threads which act like harpoons.
Once captured and immobilised, prey is pulled by the tentacles into the anemone's mouth in the centre of its body. Having been engulfed, the prey is digested and uneaten material leaves the way it came in; anemones have only one opening to their body cavity.
Individual sea anemones have been observed to live for nearly 100 years. In addition to reproducing sexually, some of these creatures can produce new individuals by budding. This sometimes happens when they walk across a rock and small pieces of their base tear off. New anemones can grow from the pieces left over.
Appeared in DIVER - November 1999