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. It's 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 North and Irish Seas and around the coast of Australia. They are mostly no deeper than around 20 metres.
Dive sites and marine life of the Calf of Man and neighbouring area by Bill Sanderson, Bruce McGregor and Andrew Brierley, Immel Publishing Ltd, 1994, Paperback.
Great British Marine Animals, by Paul Naylor, Deltor (2005)
The Underwater Photographer: Digital and Traditional Techniques, by by Martin Edge, Paperback, 536 pages (2009)