Arthropod sensilla: Morphology and phylogenetic considerations

The structures of different types of arthropod sensilla are compared and th eories regarding the evolution of these sensory organs are presented. Arthr opod sensilla are built according to a common plan, and are probably homolo gous to scolopidia. Certain similarities in the structure of sensilla in di fferent arthropod groups can be the result of adaptations to specific envir onments. The structure of sensilla in insect groups, which are regarded to be ancestral, do not appear to be less sophisticated than in groups conside red to be more advanced. The different types of pare systems, as well as th e structural differentiations of insect olfactory sensillar types remain un explained. Olfactory sensilla display a large degree of similarity among te rrestrial arthropods, whereas crustacean sensilla diverge in structure. In holometabolous insects larval sensilla appear to be structurally quite adva nced, and more complex than in the adult. During the ontogeny of both sensi lla and scolopidia, these are differentiated in an epithelial layer, result ing in the formation of both sensory and enveloping cells. The developmenta l patterns of sensilla in the studied insect groups are similar. During the development of sensilla apoptotic process are usually active. (C) 1999 Wil ey-Liss, Inc.