Steve Haddock of the the Monterey Bay Aquarium Research Institute (and author of the fantastic book, Practical Computing for Biologists) sent me a link to MBARI's latest video, about the wonderfully weird Velella jellyfish, aka the by-the-wind sailor.
In the spring, beaches can be covered by thousands or even millions of blue jellyfish relatives called Velella velella, the by-the-wind sailors. Velella typically live on the surface of the open ocean far from shore, propelled by winds pushing on their tiny sails.
Velella is best described as a hydroid colony which has flipped itself over. It is unlike a traditional jellyfish (medusa), but rather like the benthic stage of a hydroid. Instead of living attached to rocks on the bottom, its "substrate" is the ocean's surface. These hydroid colonies bud off tiny medusae, little "jellyfish", just like many benthic hydroids do.
A particularly striking feature of Velella is their blue pigmentation. In fact, most animals that live on the surface of the water (snails, jellies, fish) have blue pigmentation. It may serve different purposes for different organisms, but is likely a combination of camouflage and protection from the sun's rays.
For more information on Velella and to report your own sightings go to jellywatch.org.