Fine structure of spermiogenesis, spermatozoa and spermatophore of Saxidromus delamarei (Saxidromidae, Actinotrichida, Acari).

Ultrastructural details of spermiogenesis, spermatozoa and the spermatophore of the early derived actinedid mite Saxidromus delamarei are described. Spermatids and mature sperm cells are provided with up to four acrosomal complexes and nuclei derivatives (chromatin bodies). Due to this reason, the sperm cells may be classified as synspermia, a sperm type found only in some spiders until now. The acrosomal complex is composed of a remarkably complicated vacuole and filament. Other peculiarities of sperm structure correspond to those found in prostigmatic mites, i.e. penetration of the chromatin body by the acrosomal filament and the presence of peripheral invaginations of the plasmalemma. The sperm cells are covered by a thin secretion layer of probably proteinaceous material. Stalked spermatophores are rather large, but simply structured and contain relatively few sperm cells. The results are discussed taking systematical and behavioural aspects into account. In particular, it is suggested that the peculiar mating behaviour of these mites secures both sperm transfer and first male's sperm priority and that this allowed reduction of sperm numbers.

Moulting and morphogenesis of sensilla in a prostigmate mite (acari, actinotrichida, actinedida: caeculidae) I. Mechanoreceptive bristles.

In the prostigmate mite Microcaeculus steineri delamarei moulting and morphogenesis of mechanoreceptive sensilla were studied by electron microscopy and compared to corresponding sensilla of other arthropods. Dendritic contact with the cuticular parts of old sensilla breaks down during apolysis. Two groups of cells are engaged in the formation of new sensilla: 1) several trichogen and two tormogen cells in a semicircular arrangement, and 2) two sheath cells surrounding the mechanoreceptive dendrites. Cells ensheathing the dendrites do not play any part in the formation of bristles. These observations differ from those on insect sensilla during moulting.