Comparison of crustacean and insect mechanoreceptive setae

Mechanosensitive cells of crustacean setae show important cytological differences compared with those of insects. The mechanosensitive cells in arthropod setae can be classified in 2 groups, which are structurally and functionally different. The typical mechanosensitive cells of insect setae show a tubular body at the tip of their dendrites, whereas mechanosensitive cells of aquatic crustaceans never show such a structure and are characterized by a 9 + 0 cilium, a large ciliary root and a scolopale cell. Among crustaceans, mechanosensory cells with a tubular body are observed only in terrestrial isopods. Therefore, it seems that the type of mechanosensitive cell associated with an arthropod seta is linked more to the physical environment than to the systematic group. It is also linked to differences in the kind of mechanosensitivity of the 2 types of cells: dendrites with a tubular body are compression-sensitive, whereas dendrites with a 9 + 0 type cilium would be stretch-sensitive, The presence of one type of cell in the terrestrial organisms and of the other in the aquatic animals may be explained by the physical characteristics of the environment. (C) 1997 Elsevier Science Ltd.