• Scientific name: Velella velella
• Also known as: Sea Raft, Sail Jellyfish
• Size: Usually 10cm across
• Distribution: Generally found in the warmer waters of the world but present around the British Isles, especially around the south and west, in the summer months.

The by-the-wind sailor is a species of jellyfish which floats on the surface of the sea. A fin protrudes from the jellyfish which catches the wind and propels the creature in the direction of the wind. Generally, by-the-wind sailors are a bluish colour, although they can also be purple. They feed on plankton and the free-swimming larvae of crustaceans and fish. While the by-the-wind sailor is usually found out in the open ocean, they are at the mercy of the wind and can be washed ashore by certain conditions.

A by-the-wind-sailor stranded on a beach.

It is possible to witness strandings of by the wind sailors in Britain in Ireland which happened in December 2015 when onshore winds caused by Storm Desmond pushed large numbers of by-the-wind sailors onto beaches in Dorset and surrounding areas. The by-the-wind sailor is prey for certain species of fish such as the sunfish.