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Moon jelly, Monterey Bay Aquarium.
This alien-looking creature is named for its translucent, moonlike circular bell. Instead of long, trailing tentacles, moon jellies have a short, fine fringe (cilia) that sweeps food toward the mucous layer on the edge of the bell. Prey is stored in pouches until the oral arms pick it up and begin to digest it. Found worldwide in temperate and tropical waters, moon jellies feed in quiet bays and harbors. Although moon jellies have a sting, they pose little threat to humans.