ABSTRACT
There is still relatively little known about the natural history of gelatinous animals in the plankton, and their sensory ecology remains largely a matter of surmise, based on limited morphological, physiological and behavioral data. Pelagic tunicates are among the most widely distributed and abundant of the gelatinous zooplankton, and display a range of behavior that is apparently cued by aspects of their environment. Different kinds of information may be important for different scales of behavior. Feeding and predator avoidance are likely to be affected by near-field stimuli from visual, chemical or mechanical sources, while far-field information such as gravity, light, temperature, or pressure are likely to cue behavior spanning larger time and space scales, such as vertical or ontogenetic migration, aggregation and reproductive cycles. A variety of sensory structures have been described in pelagic tunicates, including photoreceptors of varying complexity, and several structures that have been suggested to be mechano- or chemoreceptors. Focussing on salps, this paper describes behavior that depends on sensory information, reviews the known structure and function of sensory receptors, and suggests some hypotheses on mechanisms defining the sensory ecology of these planktonic organisms.
