Like jellyfish and corals, anemones belong to the group Cnidarians. The name Cnidaria comes from the Latin cnidae which means ‘nettle’. All of the animals within this group have stinging cells which they use for the capture of prey and to protect themselves against predators. Sea anemones are simple animals, often attached to hard surfaces such as rocks and boulders. However there are also burrowing anemones that bury themselves in sand, mud or gravel on the sea floor.
Sea anemones have many fascinating methods of reproduction with some species using a combination of techniques. Some, including beadlet and daisy anemones are vivaporous (so are humans!) and reproduce through internal fertilisation, releasing fully formed young anemones from their mouths. Most anemones can reproduce asexually through budding, where fragments break off and develop into new individuals. Some stretch themselves along their base and split across the middle resulting in two new anemones of equal size. This method is called longitudinal fission. In others, small pieces of tissue break from the base forming tiny anemones. This method is called basal laceration.
Sea anemones can be found in oceans all over the world, but arguably some of the most beautiful are seen right here in Britain. Our own temperate waters support over 70 species of anenome.Beadlet anemone (Actinia equina) one of the most common in the rocky shores around the British Isles.
- Some anemones such as the snakelocks anemone glow fluorescent green under ultra violet light.
- Fish, and shrimps, can often be found hiding from predators inside the floating tentacles of anemones.
- The mouth of sea anemones is also their bottom!
- Some anemones have tiny algae living inside them, allowing them to obtain extra energy from the sun!
“How do they move?”
Most sea anemones live attached, catching passing food with their tentacles. Sea anemones can move slowly by gliding on their base. Many are also capable of moving rapidly to avoid predation or competition by detaching, catching a current and re-attaching elsewhere.
Snakelocks (Anemonia viridis) common species in the British south west coast.
“What do they eat?”
The diet of most anemones consists of small animals such as plankton, crabs and fish, however a number of bigger sea anemones will eat much larger prey. For example, dahlia anemones can be greedy feeders that will prey on starfish and jellyfish
“How do they feed?”
Anemones have rings of tentacles surrounding their central mouth. Tentacles have specialised stinging cells called nematocysts. They use these to immobilise their prey so that the tentacles are then able to move the food into the mouth. The extending tentacles can also be used to catch passing food as it drifts past.
“What is the biggest and smallest?”
Sea anemones vary in size, with some tropical species reaching more than a metre in diameter. One of the largest in British waters is the Horesman anemone (Urticina eques), reaching sizes of 35cm across. One of the smallest in Britain is the rare anemone Gonactinia prolifera, which rarely grows more than 5mm tall.Dahlia anemone (Urticina felina) in Plymouth Sound
“Where do they live?”
Anemones have adapted to a wide range of habitats, from the muddy depths of sea lochs, to seashores, wrecks and offshore reefs. Some even attach to other living creatures. The beadlet anemone is an example of a specis found on the shore, which can survive out of the water when the tide drops, by drawing its tentacles inside its body.
“How long do they live?”
Some sea anemones are very long lived and have been known to reach 60-80 years. Because anemones are able to clone themselves they do not age and therefore have the potential to live indefinitely in the absence of predators or disease.
Some species commonly found around the British Isles
Beadlet anemone (Actinia equina) – the most familiar sea anemone to most. Found on a wide range of rocky shores, often as dark red or green blobs of jelly when out of the water at low tide.
Strawberry anemone (Actinia fragacea) – similar to the beadlet anemone but larger and marked like a strawberry.
Snakelocks anemone (Anemone viridis) – another familar anemone in the south west, whose brightly coloured tentacles remain extended even when disturbed.
Gem anemone (Aulactinia verrucosa) – a squat anemone with many markings and a bumpy body. Normally found attached to rocks on the lower shore and in pools.
Cloak anemone (Adamsia carciniopados) – is a beautiful pink spotty anemone almost always found living with the hermit crab (Pagurus prideaux).