As mentioned in a previous post, jellyfish are strange creatures. Cousins of the jellyfish are no different. The strange thing pictured below is one of these. They are known as velella (but also: by-the-wind sailor, purple sail, little sail, or sea raft).
Little sails float at the surface of the oceans. They can be found across the world wherever there are temperate waters, from the California coast to Ireland. Their sails sit above the water, catching the breeze which propels them across the surface. By floating on the surface, the by-the-wind sailors feed on plankton below. But how they feed is where things take an strange turn.
Each velella is not actually a single organism, but a colony of polyps (seen in early stages of the jellyfish lifecycle). They appear as tentacles, hanging below the sea raft at less than a centimeter. Each polyp feeds on plankton, but then shares the nutrients with the rest of the colony.
Each tentacle is an individual polyp, but each polyp has it’s own job for the colony. There are two main types: gonozooids and dactylozooids. As some may remember, the polyp stage of jellyfish is what produces “baby jellyfish” (ephyra). Strangely, velella are actually a stage in some species of jellyfish, with the gonozooids producing ephyra! In order to protect the reproducing gonozooids from harm (after all, they do hang just below the water’s surface), dactylozooids use stinging cells to drive away predators. While not a deadly toxin to humans, you wouldn’t want to rub your eyes after getting stung!