SENSORY SPECIALIZATION ALONG THE FIRST ANTENNA OF A CALANOID COPEPOD,PLEUROMAMMA-XIPHIAS (CRUSTACEA)

A morphological map of the sensory setae on the first antennae of Pleu romamamma xiphias was made utilizing light and electron microscopy. Ou r results indicate that: 1) purely mechanoreceptive setae are located only on the most distal segments; and 2) chemoreceptive and mixed-moda lity mechano-/chemoreceptive setae are located along the entire antenn a with the greatest abundance in the proximal third of the antenna. Th e aesthetasc-like chemoreceptive setae are thin-walled and are innerva ted by many small dendrites. The mixed-modality setae, which comprised the most abundant type, are characterized by an apical pore, and they are innervated by large mechanosensory dendrites as well as smaller c hemosensory dendrites. The purely mechanoreceptive setae lack both api cal pores and the smaller sensory dendrites. We hypothesize that the f unction of the mixed-modality setae is ''gustatory'', that is, they ma y be sensing particles by tasting (chemoreception) and mechanical cont act (mechanoreception) combined. These setae may be involved in the ac ceptance and/or rejection of potential food particles which come into physical contact with the first antenna.