Chrysaora fuscescens, the Pacific sea nettle or West Coast sea nettle, is a widespread planktonic scyphozoan cnidarian—or medusa, "jellyfish" or "jelly"—that lives in the northeastern Pacific Ocean, in temperate to cooler waters off of British Columbia and the West Coast of the United States, ranging south to Mexico.

Since about the mid-20th century, C. fuscescens has proven to be a very popular cnidarian to feature at aquariums (and even some zoos with aquatic exhibits), mainly due to the public's fascination with their bright colors and extremely long tentacles.

The origin of the genus name Chrysaora lies in Greek mythology, with Chrysaor, brother of Pegasus, the son of Poseidon and Medusa.

[4] C. fuscescens feeds on a wide variety of zooplankton, crustaceans, salps, pelagic snails, small fish as well as their eggs and larvae, and other jellyfish.

Despite having a potent sting, some animals, apparently, are not bothered or affected by the defense mechanism at all; C. fuscescens often falls prey to many marine birds, large fish and some cetaceans, and is especially relished by leatherback turtles.

Sometimes they pick up hitchhikers, including small fish and crabs, which hide inside the sea nettle's bell and may feed on it.

[5] The Chrysaora fuscescens use light sensing organs called ocelli to migrate from the deeper waters of the ocean to the surface.

The life cycle of C. fuscescens begins when females catch sperm released by the males to fertilize the eggs she has produced and is holding in her mouth.