Locomotion and visual behaviour of mid-Water crustaceans

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Abstract
Video recordings were made of the behaviour of hyperiid amphipods and other mid-water crustaceans in a tank lit from above with a dim VDU screen, and from behind with infra-red light. Computer-generated stimuli could be moved across the VDU screen. Amphipods swam at speeds up to 19 body lengths per second. Some (Brachyscelus, Phrosina) consistently swam inverted, rolling from side to side. Others (Platyscelus, Parapronoe) spent periods of time rotating in the water with the dorsal acute zone of the eye pointing upwards. Both behaviours are interpreted as forms of visual scanning. Different species were active at different light levels, Phronima preferring the dimmest illumination. Three kinds of visual behaviour were seen consistently. The animals dropped from the surface as a dark square passed above them; they tracked other individuals (Hyperiids) or, in the case of Euphausiids, the stimuli on thescreen above; and they occasionally swam towards each other and collided, apparently deliberately.