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This study describes and quantifies the ultrastructural design of some cuticular protuberances in the Diptera-Brachycera that appear to have a specialized mechanical function. The microsculpture of membranes in the transitional areas of prothorax-neck, neck-head, head-mouthparts, and in the articulations thorax-coxa and coxa-trochanter was investigated in eight species from six families (Tabanidae, Stratiomyidae, Calliphoridae, Syrphidae, Muscidae and Drosophilidae) by means of scanning electron microscopy. The membrane armatures are single or grouped microtrichia, often located on microplates in the flexible membrane. The different membranes were compared using the following details: microtrichia length, microplate length and width, the shortest distance between microplates, and the number of microtrichia per microplate. Five different types of microstructure were observed: (1) single short papilla-like microtrichia directly arising from the flexible membrane, (2) single elongated microtrichia directly arising from the flexible membrane, (3) single microtrichia located on small areas of the inflexible cuticle, here called microplates, (4) microtrichia groups located on the microplates, and (5) microplates without microtrichia in the flexible membrane. The study reveals the differences in the surface ultrastructure of membranes between different parts of body and between different taxa of flies. The prothorax-neck transition is less specialized in membrane armature as compared with the head-neck articulation, and especially with that of the head-proboscis. The head-proboscis transition has the most complex membrane armature of those species studied. The membrane of the basal joints of the legs has larger plates and a higher number of microtrichia per plate than that of the more distal joints. The complexity of the membrane armature depends on the dimensions of the animal: the smallest species have short ungrouped microtrichia or micropapillae, whereas large species have the highest degree of grouping, the longest microtrichia, and the largest microplates. Three main mechanical functions served by the different armored membranes are suggested, based on the specific characteristics of the microsculptural design: (1) fixation of the folds, (2) prevention of folding, and (3) determination of direction of folding.
