Organization of dermal glands and characteristic of secretion in the freshwater mite, Limnesia maculata (O. F. Müller, 1776) (Acariformes, Limnesiidae).

Abstract

The presence of dermal glands is a synapomorphy in the freshwater mites-the large branch of the hyporder Parasitengonina. Dermal glands of the mite Limnesia maculata (O. F. Müller, 1776) (Acariformes, Limnesiidae) were studied using light and electron microscopy (TEM and SEM) for the first time. Two types of dermal glands were recognized in adult mites-14 pairs of the uniformly organized common dermal glands scattered throughout the entire body volume, and one pair of the characteristic so-called idiosomal dermal glands centrally located and stretched along the ventral body wall, supposedly corresponding to the epimeroglandularia 4. The common dermal glands are composed of a single large alveolus with the basally located columnar epithelium. An intra-alveolar lumen is positioned above the epithelium and packed with a secretion in the form of long curved electron-dense bands. These bands are directed to the excretory opening and released to the outside in the form of strongly coiled bands. The cytoplasm of the common dermal glands is filled with short RER cisterns and shows few characteristic Golgi bodies with round dense secretory granules at the distal pole. In contrast, a large elongated sac represents the idiosomal dermal glands having a relatively thin secretory epithelium on the periphery. The cuboidal epithelial cells contain areas with tightly packed RER cisterns and weakly recognized Golgi bodies. The apical cell surface bears irregular short microvilli. The large intra-alveolar lumen always contains an electron-dense secretion with myriads of small lighter particles. This kind of secretion was never seen released through the opening. The excretory opening of the common and the idiosomal dermal glands shows differences in its organization but basically is represented by a cuticular "bell" narrowing to the opening and showing a particular kind of valves at the inner side of the flaps of the orifice.