A free diver off the Pembrokeshire coast has filmed a giant lion's mane jellyfish, estimated at 10 to 15 metres long, describing it as "the length of a bus" and the first he had seen in Welsh waters. Iestyn Morgan, a 21-year-old conservationist who films marine life to highlight threats facing the seas, initially mistook the creature for the smaller, more common compass jellyfish before realising its true scale. Experts say sightings of the species, which usually inhabits colder Scottish waters, are becoming more frequent along the Welsh coast, fitting a wider pattern of warm-water species appearing in the area.

Lion's mane jellyfish bodies can reach 3 metres across, but their tentacles can trail more than 30 metres, making them among the longest animals on Earth. Marine biologist Dr Cathy Lucas of the University of Southampton confirmed the sting is the "nastiest" in the UK but not dangerous, advising people not to touch the tentacles and to flick off any stray fragments before rinsing the area in warm water. Morgan said he wants his footage to make aquatic environments more accessible to the public without disturbing the wildlife he films.