Jellyfish are also known as cnidarians, and they are found in nearly every ocean in the world. While they may look harmless, most jellyfish have stinging tentacles that allow them to paralyze or even kill their prey before they pull the creature up to digest it.
Jellyfish are opportunistic predators. This means that they are likely to eat whatever they come across, and though some jellyfish species are confined to eating only small fish eggs, others can kill and eat entire fish.
When you want to figure out what different kinds of jellyfish eat, you should look at their structures. Jellyfish have round, jelly-like bodies and at the center of this body along the bottom, you will find a small hole. The tentacles feed the food up into that hole, and in the case of some jellyfish, which are transparent, the food can be seen even after it enters the jellyfish's body. No matter what the jellyfish eats, it has to be able to push the food through that small hole. In some cases, jellyfish will kill their prey and then be unable to devour it as it is too large.
When asking "What do jellyfish eat?" it is important to remember that they are carnivores. This means that they do not eat any sorts of plants or growing things. Instead, they can eat a wide range of animals. Some smaller jellyfish will only eat plankton, a term which refers to very tiny, floating sea animals, like brine shrimp. Other jellyfish, which are larger, will eat fish eggs, while others that are larger still will devour crustaceans like sea snails and crabs. The very largest jellyfish will eat small fish. Jellyfish may also be cannibalistic, meaning that they will easily eat their own kind. Once again, this is all a matter of size; if the jellyfish believes that it can push the smaller animal into its mouth, it will attempt to do so, even if the other animal is a jellyfish.