This is a photograph of a freshwater jellyfish called medusa found in bodies of water such as Keystone lake in Pennsylvania. This is a ventral (or underside) view of a mature medusa. The whitish structure near the center is the mouth of the jellyfish. The four structures surrounding the mouth are the gonads (organs that produce reproductive cells). A mature medusa is 20 to 25 millimeters in diameter (about the size of a quarter).

Most jellyfish are marine animals, although some, such as the special medusa above, have adapted to fresh water. The medusa begins its life as a polyp-like structure. In its mature stage, it is a predator, with stinging cells that can kill small creatures.

Pictures and text provided by scientist Terry Peard. Check out the Freshwater Jellyfish Page.

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