Ultrastructure of the neck membrane in dragonflies (Insecta, Odonata)

This study describes and quantifies the microsculpture and ultrastructural design of the neck membrane of adult Odonata using scanning and transmission electron microscopy. The membranous cuticle has a complex pattern of microfolds, which appear to have a specialized mechanical function. The membrane has two layers of cuticle: the epicuticle and exocuticle. The outermost layer is the electron-opaque epicuticle, which repeats the shapes of the microfolds. The epicuticle has no fibrillar elements. The exocuticle is electron-lucent and rather thin (0.5-1.5 mu m) compared with the sclerite cuticle. The cuticle microfibrils in successive lamellae are at angles to each other. The epidermal cells underlying the membrane have an electron-lucent matrix filled with electron-opaque spherical vesicles of 0.1-0.4 mu m in diameter. The behaviour of the membrane folds under loading was studied by shock-freezing experiments; these showed that the shape of the folds changed in response to head movements, and stretched under loading. A comparison of the surface patterns of the membrane in 10 odonate species from seven families (Zygoptera: Coenagrionidae, Lestidae, Megapodagrionidae; Anisoptera: Cordulegastridae, Aeshnidae, Corduliidae, Libellulidae) had not revealed any correlation of the measured parameters with the size, sex or systematic position of species studied.