Chemically regulated feeding by a midwater medusa

Planktonic cnidarians are principal predators in the vast habitats between the ocean's surface and the deep‐sea floor. Almost nothing is known, however, about the chemical ecology of these fragile midwater animals because of difficulties associated with collecting healthy specimens and con‐ducting experiments in the field. With the use of a remotely operated vehicle, we found that the hydromedusa Mitrocoma cellularia is not a passive “drift‐net” predator. This relatively simple gelatinous organism reacted to both the taste and smell of prey in the laboratory and in situ. Our results comprise the first definitive demonstration that a species of pelagic cnidarian responds behaviorally to chemical signals, and they lend new insight into the role of chemoreception in structuring mid‐water communities.