Scallops track moving visual stimuli with their extensible sensory tentacles

Above, a bay scallop (Argopecten irradians) tracks a moving visual stimulus with its extended sensory tentacles. The stimulus is a black vertical stripe 24° wide (as measured from the center of the behavioral arena) moving at an angular velocity of 2.5°/s. The video is a loop showing the visual stimulus moving from the scallop’s dorsal (hinge) side to its ventral side, and then moving back in the opposite direction. From the video, it can be seen that the sensory tentacles on the side of the scallop facing the visual stimulus (the posterior side of the animal) are responding differently than those on the opposite (anterior) side of the animal: more of the sensory tentacles are extended, the extended tentacles reach further away from the scallop, the extended tentacles display more motion, and most of the extended tentacles track the moving visual stimulus along at least part of its path.