Cannonball jellies are a rare sight on the Pacific Coast, occasionally appearing off San Diego and areas south down to Ecuador.  They are a far more common coastal species during late spring and summer along the U.S. Gulf Coast and other areas in the Gulf of Mexico, tropical Atlantic and Caribbean.  Often they litter beaches during these months.  Fortunately the sting is barely felt by most people, although it's still a good idea to avoid contact.  If you pick one up off the beach it feels distinctly unlike a typical jellyfish - the tissue is dense and rigid and holds its shape even when not supported by water.  Cannonball jellies are strong active swimmers.  They are impressive beasts, with a bell diameter up to 18 cm.  Like other rhizostome jellies, they lack marginal tentacles, and use 8 oral arms that are compacted into a stiff feeding structure.  The bell color is variable, being bluish or yellowish, and typically darker around the margin.  A variety of small zooplankton prey are collected by the oral arms.  This jelly is one of the few that are commercially harvested for food.  It can be eaten after treatment with salt and alum.  

All photographs © David Wrobel and may not be used or copied without permission!