Chrysaora achlyos

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Southern California to Baja California, occasionally as far north as the Monterey peninsula.
0.50 - 1.50 m bell diameter, as adults.
Zooplankton, other jellies, possibly small fish.
Useful Facts or Characters: 

Dark purple, red, or black in color.  Oral arms may be 5 to 6 meters in length.

Natural History: 

Common name is the black sea nettle. Blooms occur periodically, generally in the summer (June to September).  There is some suggestion that the appearance of blooms may be associated with environmental disturbances such as El Nino and red tides.  Only recently described (1997), it was the largest invertebrate to be described in the 20th century.