ASSOCIATION IN A CRUSTACEAN SENSORY ORGAN OF 2 USUALLY MUTUALLY EXCLUSIVE MECHANOSENSORY CELLS

The external mechanosensory cells of Arthropoda are classified into tw o groups which are structurally and functionally different. One of the two types of cells is characteristic for exteroceptive sensory organs of terrestrial Arthropoda (mechanosensitive cell with a tubular body) , while the other type is typical of Crustacea (chordotonal-type mecha nosensitive cell). However, we show that, in an exteroceptive sensory organ of a terrestrial Crustacea (Isopoda), both types of cells coexis t. Only one sensory cell seems to be functional. These observations ar e discussed with respect to hypotheses concerning the functioning of t he two types of sensory cells, the physical environment and the evolut ionary position of Isopoda.