Motion and Locomotion
If Hydra is 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 net.
Hydra are generally sedentary or sessile, but do occasionally move quite readily, especially when hunting. They do this by bending over and attaching themselves to the substrate with the mouth and tentacles and then release the foot, which provides the usual attachment, this process is called looping. 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. 100 mm) in a day. Hydra may also move by amoeboid motion of their bases or by simply detaching from the substrate and floating away in the current.
Read more about this topic: Hydra (genus)
Famous quotes containing the word motion:
“All the phenomena which surround him are simple and grand, and there is something impressive, even majestic, in the very motion he causes, which will naturally be communicated to his own character, and he feels the slow, irresistible movement under him with pride, as if it were his own energy.”
—Henry David Thoreau (1817–1862)