Yes, they do. All jellies have specialized structures called cnidoblasts. Inside the cnidoblasts are capsules called nematocysts. Inside each nematocyst is a coiled, hollow thread. Nematocysts are triggered by mechanical (touch) or chemical stimuli. When they fire, the thread turns inside out, pierces its prey and delivers its venom. A jelly’s tentacles and oral arms are covered with thousands of these spring-loaded little death traps.
But not all nematocysts are created equal. The sting of a sea wasp can be deadly inside of five minutes. The famous “stingless” jellies of Jellyfish Lake in Palau however, have a venom so weak; you’d have to give them a good lick to have any effect at all.
But we’ve only scratched the surface here. Check back often at http://www.beachchairscientist.com for more insight about your favorite beach discoveries.
Vice President, Education Division, Director, Center for School and Public Programs, Mote Marine Laboratory