Jellyfish are not really fish at all! They are relatives of the anemones and corals. A jellyfish has no ears or eyes or nose and no brain or heart! They do not even have a head. Their body is almost totally made of water and is soft having no bones at all. Jellyfish are invertebrate animals because they do not have a spine or backbone. Their body is gooey, jelly-like, which is how they got the name “jellyfish” – even though they are not part of the fish family.
Scientists think that jellyfish have been on earth since before the dinosaurs. Some only live a few months, while others can live longer than 30 years. There are more than 200 different species of jellyfish. Some even give off light (which is called “bioluminescence”).
Jellyfish are not great swimmers and mostly drift and go with water currents. They can also swim very slowly by opening and closing the bell- shaped part of their body.
Jellyfish are found in every ocean of the world. They can have a variety of colors and come in all different types and sizes. They are usually shaped like a bowl or like a parachute, but can also be just a blob or small like a cup. They can not really hide or get away from animals that want to eat them.
Most jellyfish have tentacles, but some do not. They use these tentacles to catch food or to defend themselves. The tentacles have small special cells that can sting. Jellyfish tentacles can be smaller than one inch or more than 200 feet (longer than 2 basketball courts). The number of these tentacles also ranges from just a few to many hundred. The main body part can be very small, like the size of a grape or very large like the size of small car. Some of the largest jellyfish have been reported to weigh almost 500 pounds (almost the same weight as 3 normal size men)! Also, their bodies can detect touch and light by a kind of “net” of nerves. They eat small fish and zooplankton.