The sensory mediation of symbiosis between hyperiid amphipods and salps

Abstract

Hyperiid amphipods are open ocean crustaceans which use gelatinous planktonic animals for food, shelter, and brooding space for their offspring. These associations involve varying degrees of host specificity; and there are few obvious correlations between gross morphology of the amphipods and the types of host they choose. The mechanisms which allow hyperiids to find and select specific hosts in the water column were investigated through the sensory and behavioral basis of these symbioses in three genera of hyperiids, Vibilia, Lycaea, and Phronima, which differ in the nature of their association with a common host - salps. The investigation included the description of the distribution and morphology of sensilla on the dorsal surface of the exoskeleton and antennules of the three genera of hyperiids with speculation on their functions. The ultrastructure of the aesthetasc. sensilla of Vibilia sp. was determined for comparison with other crustacean aesthetasc sensilla, making a chemosensory function plausible. Behavioral experiments were conducted at sea which demonstrated a chemosensory basis for the host-specific associations between species of Vibilia and Lycaea and salps. Observations on the internal anatomy and behavior of Phronima are described which underscore the importance of salps to their general ecology.