Answer : 3. "tentacles"
Explanation :

Actually, the locomotor part of a hydra is not its tentacles. Hydras move by a remarkable way called "looping." They attach one end of their body to a surface and then release the other end, allowing it to move and attach again. This looping movement is facilitated by the contraction and expansion of the body, rather than the use of tentacles. Tentacles are specialized structures primarily used for feeding and defense in hydras.