Their scientific name is Velella velella, or V. velella. But they also go by sea raft, by-the-wind sailor, purple sail, little sail, or simply velella. And right now, they're strewn about the beaches of San Francisco, numbering in the thousands.

The odd-looking blue globs look like jellyfish, but they're not jellyfish. They're a member of a class of animals called hydrozoans, which includes jellyfish and coral. But though they're related to jellyfish, it's a relationship comparable to mammals and birds -- both vertebrates, but not all that similar.

The hockey-puck-sized creatures sail about the ocean surface. A little flap of translucent material acts as a sail and relinquishes their fate to the whims of the ocean winds, which have decided to deposit a whole bunch of them along the coast near San Francisco -- most of them among the sands of Ocean Beach.

Another cool photo of my favorite bridge: These Velella Velella are cruzing all over ocean beach. #bythewind #sai... pic.twitter.com/NhUEG6OjMJ— aSFOTaxiCab (@aSFOTaxiCab) July 31, 2014

That's good news for those who enjoy the many curious sights of nature; they are beautiful in their own way. But it's bad for velellas; they'll die if they're not soon carried back out to sea by the tides. Many of the creatures that washed ashore are likely already expired.

"If you pick these guys up and put them in the water and look at the under side, (you'll see) these tiny little tubular polyps and tentacles and other sort of things, which is the living part of the animal," explained Jim Watanabe, a lecturer at Stanford University's Hopkins Marine Station in Pacific Grove. "If it isn't face-down in the water then they can't make their living -- they'll dry out on beach quickly."