Country diary: huge jellyfish shipwrecked on the sands

Morfa Harlech, Gwynedd They have drifted on ocean currents for 500m years, pulsing gently towards landfall

The wave smudges out something written in the sand with a stick. I imagine it as a spell cast to charm ashore those lost at sea. And so it does, as tides ebb and flow, stranding the barrel jellyfish. These extraordinary creatures, also known as dustbin-lid jellyfish because of their size and shape, have been shipwrecked after an epic voyage.

Rhizostoma pulmo or R octopus is the largest jellyfish in British waters (they can grow to nearly 90cm in diameter) and is harvested around Wales for high-value medical-grade collagen. It feeds on plankton and its sting does not injure humans any more than do nettles; it is fed upon by leatherback turtles and sunfish.