These stunning animals are a common offshore visitor to the Oregon Coast. Their common name — By-the-Wind Sailors — refers to the clear, triangular sail at the top of the animal’s body which allows it to catch the wind and propels it across the surface. The animal will set its sail at appropriate angles to keep it from being blown ashore, although heavier winds during the spring and summer months may cause mass-strandings of the animal regardless. The By-the-Wind Sailor has no independent form of movement and will drift completely at the whim of the breeze. The animal is easily identified by the brilliant metallic blues and purples of its body. Short tentacles hang from the underside of the body.
The By-the-Wind Sailors feed mostly on plankton which they capture by stinging these tiny animals with cnidae contained within their tentacles. Their venom is considered harmless to human beings, although beachcombers are cautioned not to touch any jellies found washed up on shore. Their major predators are various mollusks, marine slugs and snails.
Although originally classified as a jelly, one recent study suggests that By-the-Wind Sailors are actually a unique species of large hydrozoan polyp (a class of predatory animals that live mostly in salt water). Debate remains over the exact classification of this animal.
These animals may be alternately known as sea rafts, purple sails and little sails. They are sometimes confused with the highly dangerous Portuguese Man-of-War.
By-the-Wind Sailors exists in the warm and temperate waters of most of the world’s oceans. They live only in the thin air-water interface at the surface of the water. They will often congregate in groups numbering in the thousands.