Hydra are simple invertebrates, with two layers of body cells. They live in fresh water. Their body is radially symmetric. They have a central cavity through which they take in food and expel waste.
As Cnidaria they have stinging cells on their tentacles. They are hydrozoa, and belong to the same order as other polyps. Most Hydra are microscopic in size. Hydras can be found in almost any unpolluted body of water. Hydras reproduce by budding. In budding, the offspring forms as a lump on the parent and eventually becomes big enough to break off and live by itself. They can move if they need to by a kind of slow somersaulting motion.
Recent research has found they produce an antimicrobial protein hydramacin, which protects their outer layer from bacterial infection.
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