Lion's Mane Jellyfish, Cyanea capillata
Photos copyright Tim Nicholson, whose underwater photographs and photo books are available from http://www.photoboxgallery.com/timnicholson.

With tentacles up to three metres long and covered with stinging cells, it's better not to get too close to the Lion's Mane jellyfish. Its body can be up to 200 cm across making it one of the largest species of jellyfish.

The tentacles are arranged in eight bunches, with each bunch containing over 100 tentacles. The oldest tentacles are often coloured dark red. They have a very severe sting that can produce blisters, irritation and muscular cramp and may even affect respiratory and heart function. Fragments of tentacles, left on buoy ropes for example, retain their stinging power.

This species does occasionally occur in large swarms, largely thought to be due to storms and tides that concentrate individuals together. They are predators, eating zooplankton, small fish and moon jellyfish.

You'll find the Lion's Mane in the cold Arctic and Pacific Oceans, the Irish and North Seas and around the coast of Australia. They are mostly no deeper than 20 metres.

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Further Reading
Great British Marine Animals, by Paul Naylor, Deltor (2011)
The Marine Life Information Network