A Million Tiny Shipwrecks: Velella

Science has made incredible bounds over the past few centuries, but unsolved mysteries still persist, even in everyday phenomena. Case in point: Velella velella. The precise nature of this common, extraterrestrial-looking cnidarian still confounds biologists. Some say it's an organism; some say it's a colony of smaller organisms. You wouldn't think such a question would be hard to settle in this day and age, but the debate rages on.

Velella – the word means "little sail" – is called sail jelly here on the North Coast, sea raft or by-the-wind sailor elsewhere, and the confusion over its basic composition is just the start of its weirdness. It also has a two-stage life cycle, giving birth to tiny jellyfish that somehow – no-one is quite sure how – come together later to form the sail-driven second stage pictured here. Far out at sea, great shoals of these tiny living sailboats run before the prevailing winds, the polyps below their waterlines straining plankton from the water.

Because they have no other means of propulsion, or even a rudder, they are liable to shipwreck on the beach in vast numbers if conditions take a turn for the unforeseen. When I was a boy, a sail jelly raid of this type, produced as it was by a radical deviation from usual wind and current patterns, signalled optimum pickings for prized Japanese glass net floats. Sadly, virtually all floats today are opaque plastic; not half as fun. But you can still smell a raid half a mile away; those tonnes of decaying flesh on the sand let you know it's happened again.

I for one am happy for it, all the same. Sail jelly raids were annual occurrences when I was a kid, but it's been years since I saw one. I was beginning to fear they'd passed onto the growing list of species we'll never see again.