Final answer:
Hydras have nerve and muscle fibers that enable them to move directionally due to the fascicular organization of their muscles and the stimulation of specific muscle fibers by motor neurons.
Step-by-step explanation:
Hydra asymmetry and directional movement are made possible by the presence of nerve fibers and muscle fibers in hydras. These nerve and muscle fibers are found in the axial and appendicular muscles of the hydra's body.
Inside each skeletal muscle, muscle fibers are organized into individual bundles called fascicles by a connective tissue called the perimysium. This fascicular organization allows the nervous system to trigger specific movements of the muscle by activating a subset of muscle fibers within a fascicle.
The motor neurons that tell the skeletal muscle fibers to contract originate in the spinal cord and brainstem. These neurons have long processes called axons, which form nerves that transmit action potentials from the spinal cord to the muscles.