Jellyfish aren’t actually fish at all but are invertebrates in the phylum cnidaria, named after their stinging cells. See their stinging cells in action in this videomicrograph.

The largest jelly, the lion’s mane, was suspected of stinging 150 people on the same day. Jellyfish aren’t aggressive towards humans but use their stinging cells as a defense mechanism. Each cell can only fire once so they don’t release nematocysts at every object that crosses their path. The cnidocytes have both mechanical and chemical receptors that control discharge. Hair cells detect touch while chemoreceptors sense chemicals released by predators and prey. When the jellyfish encounters something that doesn’t have the appropriate chemical scent the nematocyst doesn’t fire. This adaptation ensures that they don’t sting themselves! Lycra bodysuits have become the first line of human defense against jellyfish stings because they block chemical detection of human skin which prevents nematocyst discharge.

In most cases a vinegar rinse is recommended to prevent nematocyst discharge but it is important to know what type of jellyfish you may encounter before entering the ocean to prepare for proper first aid. Recent research has stirred controversy about the use of vinegar, however, authorities assert that findings are not strong enough to change public safety guidelines and more research is necessary. Those stung by the Australian box jellyfish will likely need CPR. Learn how its venom, the world’s deadliest, damages blood cells and about the discovery of a promising new treatment.

Some jellyfish are harmless to humans either because their nematocysts can’t penetrate the skin or their venom is too weak. In Palau’s Jellyfish Lake, visitors can swim safely surrounded by golden jellyfish. There’s a common myth that this species has lost its ability to sting but if its tentacles graze delicate areas, such as lips or eyelids, the nematocyst encounter might cause a tingling sensation.

Recent research has revealed that moon jellyfish ephyrae, their flower shaped larvae, can rearrange their bodies after injury to reestablish symmetry. Learning about the mechanisms driving this form of self-repair may help inform engineers trying to build self-healing robots in the future. Jellyfish research is also advancing the medical field with studies underway on the suitability of using nematocysts as needles for drug delivery.

Check out the amazing mouth of the leatherback turtle, with backwards pointing spines called papillae, and the ocean sunfish’s gill arch teeth. Both the sunfish and turtle use these adaptations to feast on jellyfish. Sometimes these animals mistakenly eat indigestible plastic bags because they look very similar to jellyfish underwater. This can lead to intestinal blockage, starvation and death. We can help keep them safe by keeping litter out of the ocean. Make sure waste gets into the proper receptacle, recycle, or replace plastic bags entirely with reusable shopping bags.

Learn more about how nudibranchs steal the jellyfish’s stinging cells and store them in their cnidosacs.

See a slipper lobster hitch a ride on a jellyfish! Many organisms associate with jellyfish for protection, transportation or to have a meal.

What’s it like to be stung by a jelly? Check out Diana Nyad's firsthand account of extreme swimming with the world’s most dangerous jellyfish.

Due to overfishing and climate change, jellyfish populations are on the rise. Lisa-ann Gershwin discusses the implications of jellyfish dominated oceans.

Next Section »