|Velella velella (Linnaeus, 1758) : By-the-wind Sailor
Phylum Cnidaria / Class Hydrozoa / Order Anthomedusae / Family Velellidae
Springtime visitors to much of the coast of California are frequently mystified by the appearance of long bluish rows consisting of jellyfish-like creatures that litter the beaches. These are actually masses of thousands of unusual mobile hydroids that normally travel at the surface with the aid of buoyant float tissue. Propelled by winds that act on a somewhat rigid triangular sail held above the float, Velella normally inhabit open ocean waters. The sail is made of a chitinous material and has a distinctive cellophane-like texture. Wind patterns in spring and early summer may cast thousands of these long-distance wayfarers onto beaches all along the U.S. West Coast. Individuals with two types of sails that are mirror images of each other exist in a population – they are thus pushed in opposite directions by the wind. Although previously classified in the Order Chondrophora, recent considerations indicate an alliance with the anthomedusae.
The float and surrounding tissues are endowed with an attractive deep blue pigment. The float contains a series of sealed air chambers that provide buoyancy. Total width of the floating polyp is usually less than 6 cm. Beneath the float is a grouping of several types of zooids, colored brown by the presence of zooxanthellae. A large central mouth is surrounded by shorter reproductive stalks with mouth openings that bud tiny adult medusae that produce eggs and sperm. Multitudes of tiny brownish-green medusae that never grow to more than 3 mm tall are cast off (last photo). These then release the eggs and sperm that produce free-swimming larvae which eventually develop into more floating polyps. It’s not known if a planula larva is produced initially, but during the early stages oil droplets are formed that bring the young Velella to the surface. Dangling beneath the rim of the float are hollow tentacles that ensnare fish and invertebrate eggs, copepods and appendicularians. Velella is found in warm and temperate seas throughout the world. Although not dangerous to people, it’s best not to handle them or touch your face or eyes if you’ve been touching beached individuals since some irritation may result.