Earlier this month a beachgoer in western Ireland spotted what appeared to be a blob of ornate, maroon-coloured marble splayed on the sand at Fanore Beach. It was, in fact, a lion's mane jellyfish (Cyanea capillata), a cold-water-loving cnidarian believed to be one of the world's largest jelly species. 

The lion's mane jellyfish with a coffee mug as a size reference. Image © Liam McNamara/Burren Shores - Beachcombing & more

Liam McNamara – administrator of a popular Facebook page called Burren Shores - Beachcombing and more – uploaded photos of the remarkable animal to his page where the images quickly gained a lot of interest.

Named for the hair-like tentacles that trail from the underside of its bell when in the open ocean, lion's mane jellyfish vary greatly in size, but those that dwell in the northern reaches of their range in the boreal waters of the Arctic can reach a bell diameter of over two metres (6,6 feet). Unlike many other species of jellyfish, lion's manes are solitary, drifting close to the ocean surface where they use their stinging, sticky tentacles to trap prey such as small crustaceans, fish and other jellies.

Lion's manes are not an entirely uncommon site along the Irish coastline, as strong ocean currents can sometimes push the animals onto the shore where they are unable to survive for long periods. Their presence usually raises some alarm from swimmers concerned about getting stung, but while the giant jellies can pack a punch, life-threatening stings are rare. Of course, it's advisable to keep your distance just in case – even washed up jellyfish have the potential to sting. 

"Jellyfish, outside of being beautiful and amazing, are actually a really important part of ocean ecosystems," biologist Nick Record of Bigelow Labs told NBC last year when a different lion's mane jellyfish washed up in Maine in the US. "They’re prey for things like sea turtles and sea birds. They draw down carbon dioxide into the food web and they can also survive in ecosystems that are highly stressed."