Antennal sense organs of Natatolana borealis (Lilljeborg 1851) (Crustacea : Isopoda)

In this study, the antennal sense organs of the scavenging isopod Natatolan a borealis are described for the first time, based on scanning electron mic roscope observations. The peduncles of the two pairs of antennae both show the same kind of organization. The sensory organs on the flagellum consist of several kinds of specialized setae possibly having a uni- or plurimodal function. These setae are either specific to one pair of antennae, or commo n to both pairs. Various types of ornamentation present on the antennae 1, such as teeth, ps eudochaetal formations and micropores, may either play a role in grooming o r serve to maintain the functional integrity of the antennae 1, which is of great importance for scavenger species such as Natatolana, in which the fi rst antennae seem to be the main chemoreceptor organs. The most important o rgans, in terms of their number and size (300 mu m), are the aesthetascs. T hese are carried by the flagellum, and seem to play a mainly chemosensitive role. It is hypothesized that the whole of the antennae 1 flagellum may co nstitute a specialized organ which is involved in chemoreceptive processes. This organ seems to be homologous to the callynophore described in amphipo ds. Natatolana borealis is endowed with setae of many other kinds. Some of them , the pocilliform setae, have a subapical pore and may have a chemosensitiv e function, while the bifid setae probably have a plurimodal function; the apical setae constitute the most frontally located chemoreceptor organs in this animal. Other morphologically different setae complete the antennal se nsory equipment: these are the tufted setae which probably participate in c ollecting particles; and the plumose setae, which have a mechanoreceptive f unction. Some kinds of setae occur in groups, forming a functional unit (tu fted setae/digited organ; tufted setae/pocilliform setae). A brief histolog ical study of the antennules showed a rather similar pattern of organizatio n to that observed in other crustacean species. The meaning and the functio n of the various structures observed here are discussed.