May 17, 2022

A meduse is one of two morphological stages of a cnidarian. The meduse is the motile, free-swimming life stage capable of sexual reproduction. The meduse is also called the jellyfish stage, because all jellyfish (especially the disc jellyfish) can mainly be recognized by their meduse. The meduse stage probably originated with the common ancestor of the Medusozoa. The other life stage of a cnidarine is called the polyp. This is the perennial phase that settles in the seabed and reproduces asexually by means of budding. The polyp stage has been secondarily lost in evolution in some cnidarians.


Cnidarians are a large group of marine animals. Four major classes are distinguished: Scyphozoa (large medus), Cubozoa (box jellyfish), Hydrozoa (small medus) and Anthozoa (flowers, with only the polyp stage). Scyphozoa have a four-part symmetry and often have a well-developed whorl of tentacles around the mouth and rim of the body. Cubozoa have a box-shaped body and can often move quickly. Hydrozoa medus are small and have reduced tentacles. Although the jellyfish show a great wealth of shapes, all representatives have the same building plan in simple lines. The body of a meduse is made up of a translucent, jelly-like substance (the mesoglea) and is generally umbrella- or bell-shaped. A stem-like structure hangs down from the center, the manubrium, which contains the mouth opening. The mouth is connected to the gastrovascular cavity, the place where digestion takes place and nutrients are absorbed.

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