These are sea nettles, part of the Monterey Bay Aquarium's huge collection of jellyfish. As the aquarium puts it, "A sea nettle is well armed for capturing food," reads a sign at the aquarium. "See those wispy tentacles? They fire thousands of tiny stinging cells that paralyze prey. Then the jelly transfers its catch to those frilly mouth-arms and finally to its mouth, where the jelly eats its meal."