Velella velella (Va-le-lia)
- Mobile hydroids that normally travel at the surface with the aid of buoyant float tissue.
- Propelled by winds that act on a rigid triangular sail held above the float, inhabit open ocean waters.
- The sail is made of a chitinous material and has a distinctive cellophane-like texture.
- Individuals with two types of sails that are mirror images of each other exist in a population - pushed in opposite directions by the wind.
- 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.
- 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.