The by-the-wind-sailor is not a jellyfish, but a colony of polyps which cohabitate. The famous Portuguese man-of-war is also such a colony. The polyps have various functions: eat, reproduce, deterrence. Together, they form an oval disk, which drifts on the waves. The by-the-wind-sailor has a triangular sail on this round disk. Using its sail, this organism travels the world seas. Sometimes, a group of them cross the ocean from the Caribbean region and land up along the European coasts.