The multifunctional sensory complex in the antennae ofAllacma fusca (Insecta)

Abstract

The antennal-tip sensory complex inAllacma fusca (Collembola) was reconstructed from serial ultrathin sections. The complex contains 16 sensory cells which belong to three spatially separated subunits: (1) a sensory hair; (2) a cuticular protrusion, containing two highly-specialized dendritic outer segments from a single sensory cell encapsulated by an enveloping cell and a gland cell (Figs. 4 and 5); and (3) two sensory cells with partly lamellated, double dendritic outer segments located well away from the cuticular surface (Fig. 3). A phylogenetic evaluation reveals a mosaic of apparently primitive characters, and trends toward higher structural complexity as well as toward reduction (Table 1). There is support for a hypothesis that the receptors of the sensory hair are chemosensitive. The functional interpretation of the other components of the complex is problematic due to their unusual structural properties. The sensory cell beneath the cuticular protrusion is considered to be proprioceptive.