Ultrastructural investigations of the salivary glands in adults of the microtrombidiid mite Platytrombidium fasciatum (C. L. Koch, 1836) (Acariformes: Microtrombidiidae)

Abstract

The organization of the salivary glands in ad libitum-fed adult females of the microtrombidiid mite Platytrombidium fasciatum (C. L. Koch, 1836) was observed using transmission electron microscopy. In all, four pairs of large simple alveolar salivary glands were determined, which have been named due to their position as posterior, ventral, medial and dorsal. These glands occupy a body cavity behind, around the base and partly inside the gnathosoma. The posterior glands are largest and possess large nuclei with greatly folded nuclear envelope. Secretory granules are electron-light, containing fine granular material and are partly provided with various lamellar inclusions inside the granules. The latter tend to be placed predominantly in the middle parts of the gland around the central (intra-alveolar) cavity. The remaining glands, conversely, are typically filled with tightly packed electron-dense secretory granules, except for the ventral glands, the granules of which may show a compound organization. The nuclei of all these glands occupy a peripheral position and are mostly pressed between the granules. No prominent endoplasmic reticulum or conspicuous Golgi bodies were observed within the salivary glands. The salivary glands are provided with a complex apparatus of the intra-alveolar cavity (acinar lumen) with the excretory duct base provided by a system of branched special cells producing the duct walls. The ventral glands open by separate ducts into the most posterior part of the subcheliceral space. Ducts of the posterior glands immediately fuse with the ducts of the tubular (coxal) glands. The common duct of each side of the body joins with the ducts of the medial and dorsal glands respectively, and opens into the subcheliceral space far anterior to that of the ventral glands.