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The Seashore

Snakeslock Anemone (Anemonia viridis)

The Snakeslock Anemone

The Snakeslock Anemone can be found in two colour forms. The normal colour is a grey-purple whilst the second is where an alga has colonised the cells and turned it green. This is a harmonious arrangement (symbiosis: where two organisms are living together amicably)

The sting cells (nematocysts) paralyse the prey and are triggered to fire by proteins on the surface of the food. They feel sticky to the touch as they fire the "harpoons" into the skin. As a carnivore, it feeds upon crustaceans, including crabs, shrimps and small fish. The Snakeslock and others except the Beadlet, cannot contract their tentacles inside the body when the tide recedes and are usually restricted to rock pools and lower down the shore. They tend to live in a crevice or under large seaweeds Fucus to prevent any significant loss.


Some Snakeslock are green and this is due to a symbiotic association that has arisen. The green is due to a dinoflagellate alga called Symbiodinium. This alga lives inside the cells of the anemone, separated from the cell contents by a membrane. As long as the anemone stays in the sunshine the algae can photosynthesise inside the cells of the animal, which provides protection and basic nutrients like carbon dioxide. In return the algae gives up complex lipids (fats) and glycerol. This is sufficient to fuel the anemone so that it does not have to feed. The association builds up as the young anemone starts to feed. However, some anemones are infected from birth as the eggs actually carry some algae across into the next generation. Due to the wealth of food that the Snakeslocks can obtain in this way they may form dense colonies, all genetically similar, by asexual reproduction. Those that are green tend to live in shallow rock pools. Sperm is released by the male into the water. Here they swim and internally fertilise the females eggs. She eventually releases minute sea anemones.

A widespread species including the Mediterranean. Not found on the east coast of the UK but common in the west. Found on the middle and lower seashore.

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