Although by-the-wind-sailors live out at sea you will sometimes find them washed up on the Irish coast. They are made up of an oval disc or ‘float’ a few centimetres long with a sail sticking up from it, which allows them to catch the wind and drift on ocean currents. They also have tiny stinging tentacles coming from the base of the float which catch their prey, mainly plankton, however the tentacles are not dangerous to humans. 

By-the-wind-sailors look like they could be related to a jellyfish. This creature is, however, thought to be more like an upside-down and floating variation of hydroid, a class of organisms that is usually found attached to the sea floor. To make things more complicated, they are in fact considered a hydroid colony which is not just one creature but is made up of many tiny individual organisms.  

They are a blue/purple colour but if washed out and dried up they will often have lost their colour and can look a bit like clear plastic. Sometimes they can be washed up in large numbers after storms out at sea. In 1992 millions of By-the-wind-sailors were washed up along the West coast of Ireland in one episode. 

On some by-the-wind-sailors, the sail is set NW-SE; on others, NE-SW. This means that in the same wind, one animal will sail leftwards, the other to the right. This means that the species gets scattered in all directions across the oceans.