- 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.
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, as well as sea snails.