Ultrastucture and functional morphology in mites: current knowledge and future perspectives

Ultrastructure in biology is the study of the minute structures characterizing cells or tissues. These features are not visible through an ordinary microscope but can be seen only with the high resolution and magnification range of a transmission electron microscope (TEM) or with scanning electron microscopy (SEM). On the other hand, functional morphology uses these structures to understand the connection between an organism form and its behavior: function from form. The first electron microscope was realized in 1931 increasing immensely the range of observable structures. Nevertheless, electron microscopy came into use in Acarology in the late 1960s with SEM the most widely used. Textbooks and many research papers in biology anatomy and morphology used electron micrographs of the whole specimens (SEM) or ultra-thin sections (TEM) to support evolutionary and functional interpretations. Moreover, during the 21st century, several new techniques for two-dimensional (2D) and three-dimensional (3D) ultrastructural studies of cells, tissues, and organs have been developed. Still, detailed knowledge of internal features of functional relevance is limited or even lacking in several groups of mites and it is essential to acquire much more comparative information from a variety of groups before meaningful generalizations can be made.