Integumentary "rosette-like structures" in Microcoryphia and Zygentoma (Insecta): SEM morphological and topographic surveys

Abstract

"Rosette-like structures" (RS) were found previously on integument of different body regions of Microcoryphia and Zygentoma. Their putative functions, either as sensilla or as openings of epidermal glands, are still not clear. This study was carried out as the initial descriptive stage of a special investigation of RS. For the first time, the morphology and topography of RS in nine species of wingless insects, including enigmatic silverfish Tricholepidion gertschi, were examined specially by means of scanning electron microscopy. Rosette-like structures were found in all studied species except for an atelurid Nipponatelura shirozui. They were numerous, mainly on the unscaled body appendages. Solitary RS were distributed randomly on most surfaces of the insect body, except for the antennal flagellum of all studied representatives and the caudalia of zygentomans where RS were arranged among rows of bristles and sensillae. Some of clustered RS were closely positioned to joints or articular membranes. The female genital appendages exhibited quite a peculiar pattern of RS distribution. The RS were tentatively categorized into five basic morphological types. There is considerable variation in morphology of RS among members of the Microcoryphia, which probably reflects functional heterogeneity of RS. On the contrary, RS of zygentomans mainly belong to one morphological type, whereas another one of RS-types was found in T. gertschi only. The homologization between highly variable RS in Microcoryphia and morphologically uniform those in Zygentoma currently seems to be unfeasible. © 2010 The Entomological Society of Japan.