[Turning over in the ophiuroid Amphipholis kochii].

The reaction of turning over in the ophiuroid A. kochii Lütken begins when the ambulacral legs are detached from the substrate. At the bottom, when aboral side of the animal touches the substrate, turning over begins with oral flexion of three arms. In water, turning over begins with aboral flexion of all the arms. The organism takes the shape of a ball, its center of gravity being shifted to the side of a disc which outer surface is formed by the oral part. As a result, when dropped into the water with its oral side upwards, the ophiuroid passively turns over due to the gravity force. Single arm isolated together with the adjacent part of the nervous ring is capable of turning over. After sectioning the nervous ring, coordinated activity of the arms during turning over is disturbed.