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

Abstract

In this study, the antennal sense organs of the scavenging isopod Natatolana borealis are described for the first time, based on scanning electron microscope 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 common to both pairs.

Various types of ornamentation present on the antennae 1, such as teeth, pseudochaetal formations and micropores, may either play a role in grooming or serve to maintain the functional integrity of the antennae 1, which is of great importance for scavenger species such as Natatolana, in which the first antennae seem to be the main chemoreceptor organs. The most important organs, in terms of their number and size (300 μm), are the aesthetascs. These 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 constitute a specialized organ which is involved in chemoreceptive processes. This organ seems to be homologous to the callynophore described in amphipods.

Natatolana borealis is endowed with setae of many other kinds. Some of them, the pocilliform setae, have a subapical pore and may have a chemosensitive 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 sensory equipment: these are the tufted setae which probably participate in collecting particles; and the plumose setae, which have a mechanoreceptive function. Some kinds of setae occur in groups, forming a functional unit (tufted setae/digited organ; tufted setae/pocilliform setae). A brief histological study of the antennules showed a rather similar pattern of organization to that observed in other crustacean species. The meaning and the function of the various structures observed here are discussed.

Keywords:

• Crustacea Isopoda Natatolana Scavenger Sense Organs Antennae Scanning Electron Microscope