Interesting Animals: By-the-Wind Sailor

By-the-wind sailors (Velella velella) stranded on a beach

These fairly small creatures are somewhat similar the more well known Portuguese man-of-war. Instead of a large float, however, the by-the-wind sailor has a sail that extends vertically from its tissue that allows them to be carried by the wind. They are most often seen stranded on beaches, where they may come to shore in very large numbers. They are found in the warm waters and these strandings are a consequence of wind travel. The sail is actually angled along the body axis at an approximately forty-five degree angle and points toward the beach that will eventually be the animal's resting place.

A better view of the sail and size

Structure-wise, it is basically one upside-down polyp that settled on the water's surface rather than the ocean floor. It's quite small at only a couple of centimeters across. A carnivore, it can only catch what food is within its reach. Since it is so close to the surface, this is usually only very small bits of food. The species is also prey to some other animals. They are sometimes grouped with the Portugese man-of-war, but the two have a number of structural differences. One major one is the colonial structure of the man-of-war being so different from the single polyp of the by-the-wind sailor. The by-the-wind sailor was, however, once thought to be colonial as well, and was thus placed in the same grouping as the man-of-war.

Source is Animal Diversity Web. Images are from Wikimedia Commons and are copyright free: one, two.