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Here’s a tricky one: a jellyfish is neither jelly nor a fish! If you’ve ever seen one drifting about in the water, you might think it was made of jelly, because it has such a floaty, flexible appearance.

In fact, jellyfish are 97% water, and have no heart, blood, brain or gills. However, they can smell, taste and remain balanced in the water. The bell, or body, of a jellyfish has at least one mouth on its oral surface, and they feed on tiny zooplankton, which drift about in the ocean much like jellyfish do.

The tentacles of the jellyfish dangle from the bell like long, stringy arms. Tentacles help to trap food for the creature and can—in the case of the arctic lion jellyfish—extend as long as 100 feet in length. Some jellyfish carry poisonous stinging cells in their tentacles. The stinging cell contains a capsule with a sensory hair, a lid and a nematocyst that does the stinging. When the sensory hair is stimulated by another creature’s movements, the nematocyst fires like a harpoon from the capsule. This stinging reaction occurs in just seconds, and is one of the fastest cellular processes in nature. Not bad for a creature without a brain!

Not all jellyfish are poisonous, however. There are over 200 types of jellyfish found throughout the world’s waters. Because they have no backbones, jellyfish are categorized as invertebrates. Their phylum name is Cnidaria, which comes from the Greek word, cnidos, meaning “stinging nettle.” Guess the Greeks figured out the nematocyst reaction way back when.

Jellyfish swim using jet propulsion whereby the coronal muscles, found on the underside of the bell, force water out of the domed bell. As the water is pushed out in one direction, the jellyfish is propelled in the opposite direction. A simple yet effective mode of transportation, wouldn’t you agree?

Although you must be wary of unidentified jellyfish—even if they appear to be dead on the shore—most jellyfish are not poisonous. In fact, some are beneficial to other animals, such as some types of tiny fish and crabs. These creatures are able travel under the protective bell of the jellyfish host. Believe it or not, some types of jellyfish are being used in cancer and heart disease treatment! Keep your eyes open for jellyfish the next time you are out on the ocean, now that you know a bit about these graceful creatures. Not everything is as it appears!