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Mystery over rare sea slug found washed up on UK beach | News UK

Published

3 hours ago

21 June 2026

NewsAdmin

The rare creature was found by a dog walker (Picture: Daily Post)

A giant marine slug was found beached in Anglesey by a dogwalker, baffling some experts.

The bizarre creature was later identified as a sea hare, a marine snail more commonly called a ‘sea slug’.

Smaller sea hares are native to the UK, but the Trearddur is thought to be a much rarer creature, usually found in the Mediterranean.

Emma Leese came across the sea hare some 20 metres from the water’s edge at low tide. Worried that local dogs might take too much of an interest, she returned it to the sea.

‘When back in water, it sort of unfolded,’ she said. ‘It began wriggling – slug-like – and its stalks began going back up.’

As sea slugs cannot absorb atmospheric oxygen, they typically die relatively quickly after stranding.

When disturbed in water, they release a dramatic cloud of purple ink derived from the red algae they eat.

Like the octopus, this ink is thought to provide a screen or act as a decoy to confuse predators.

Owner and director of Anglesey Sea Zoo, Frankie Hobro, said it’s more likely the creature is a depilatory sea hare.

He added: ‘This is still a rare UK species, found occasionally in southwest Britain.

‘However, it’s a species we’re likely to see more of in the future as the seas warm and they keep moving north.’

According to the Global Biodiversity Information Facility, the Isle of Man has three confirmed sightings of the depilatory sea hare, and north Scotland has one. Wales has none, though there have been anecdotal reports in Pembrokeshire.

As a mollusc, sea hares are related to the common garden snail. Instead of an external shell, they have a thin, transparent internal shell.

Their fleshy mantles have become modified into large, wing-like flaps. The depilatory sea hare can use these to gracefully swim through water – it is said to be surprisingly agile.