THE PHOTOTACTIC BEHAVIOR OF THE STARFISH, ASTERIAS AMURENSIS LÜTKEN

¹ Tamano Marine Laboratory, Shibukawa, Tamano, Okayama, Japan

1. The starfish, Asterias amurensis, was positively phototactic when light-adapted.

2. Shading four arms caused animals to start moving with the illuminated ray forward. The direction of changes in locomotion of moving animals was highly predictable when the animals were properly stimulated by partial shading.

3. The response of changing direction involved two phases, the initial and the later. In the initial phase, animals tended to move opposite to the shaded arm(s) and in the later phase, the direction gradually returned towards the original leading arm.

4. When moving, animals assumed a typical advancing posture. Shadows cast on them induced off-responses in the anterior three arms, but when animals were stationary, the off-response appeared in all the five arm tips. The relation of these reactions with the changing direction has been discussed.

5. Experiments using preparations lacking ocelli or arms, as well as those with the radial nerve transected, suggested that the apparent positive phototaxis was induced mainly by shadows which were perceived through ocelli. Light seemed to play a secondary role. The function of an extra-ocellar light sense was recognized, but it appeared only when all the ocelli were removed.

6. The central mechanism involved in controlling the locomotory direction has been discussed.