Editing Hydra (genus) (section)

==Motion and locomotion==
[[File:Hydras (8).JPG|thumb|upright|''Hydra'' attached to a substrate]]
If ''Hydra'' are alarmed or attacked, the tentacles can be retracted to small buds, and the body column itself can be retracted to a small gelatinous sphere. ''Hydra'' generally react in the same way regardless of the direction of the stimulus, and this may be due to the simplicity of the nerve nets.

''Hydra'' are generally [[Wiktionary:sedentary|sedentary]] or [[Sessility (zoology)|sessile]], but do occasionally move quite readily, especially when hunting. They have two distinct methods for moving – 'looping' and 'somersaulting'. They do this by bending over and attaching themselves to the [[Wiktionary:substrate|substrate]] with the mouth and tentacles and then relocate the foot, which provides the usual attachment, this process is called looping. In somersaulting, the body then bends over and makes a new place of attachment with the foot. By this process of "looping" or "somersaulting", a ''Hydra'' can move several inches (c.&nbsp;100&nbsp;mm) in a day. ''Hydra'' may also move by [[Amoeboid movement|amoeboid motion]] of their bases or by detaching from the substrate and floating away in the current.