Phototaxis in Two Shallow-Water Species (Crustacea: Tanaidacea).

Different crustacean species can differ in their response to light. In Tanaidacea, a small group of aquatic, benthic crustaceans, previous studies suggested that several species may be positively phototactic based on their attraction to nocturnal light traps, but no experimental investigations of phototaxis had been conducted on this group. Here we show experimentally that two species in the genus are phototactic but exhibit opposite reactions to light; , which inhabits the blades and stipes of seaweeds, was positively phototactic, whereas , which inhabits muddy sediments overlying bedrock, was negatively phototactic. This differential response may reflect differences in photoenvironment between these species' microhabitats.