A Comparison of Antennulestructure in a Surface- and a Cave-dwellingcrayfish, Genusorconectes (decapoda,astacidae) By

CrayŽ sh show many behavioral and morphological adaptations that serve to exploit chemical information in an aquatic environment. The primary chemosensory structure, the outer branch of the antennule, varies morphologically among species. A reasonable approach to the study of these variations is to compare morphological structures from crayŽ sh living in different environments. The potential of this approach was evaluated by comparing the morphology and distribution of chemosensory sensilla (aesthetascs) along antennules of a caveand a surface-dwelling crayŽ sh. In comparison to the surface-dwelling species (Orconectes cristavarius), the cave-dwelling species (O. australis packardi) had longer antennules and longer individual aesthetasc sensilla. The surface species, however, had signiŽ cantly more aesthetascs per annulus and a higher density of aesthetascs towards the distal end of the antennule.These data are discussed in terms of chemical sensitivity and chemoreception in turbulent environments.