Anatomy and ultrastructure of mitgut in the water mite Piona carnea (Koch, 1836) (Acariformes: Hydrachnidia)

Abstract

Midgut of adult mites Piona carnea (Koch, 1836) was investigated in transmission electron microscope and on semi-thin sections. The midgut ends blindly and is composed of the middle portion (ventriculus) and two paired diverticula running forward and backward as well as of the middle unpaired diverticulum located in the frontal body region. The midgut epithelium is formed of one type of digestive cells throughout the ventriculus and diverticula being, however, in different physiological conditions and located freely in the midgut epithelium. The cells in different physiological conditions may be conventionally characterized as (1) the reserve cells, (2) the cells rich in nutrition vacuoles and (3) the excretory cells. The reserve cells are flat cells forming the midgut wall. They are inactive with respect to the digestive processes. The cells rich in nutrition vacuoles are strongly hypertrophic and contain numerous nutrition vacuoles, reserve nutritive such as glycogen and lipids as well as spherites. The apical cell zone shows intensive endocytotic processes. Digestion is realized by the intracellular type. The excretory cells are the cells, which have already completed the intracellular digestion. They are characterized by the very thin cytoplasmic layer applied to the cell membrane, whereas the remaining cytoplasm is filled with the extremely large clear vacuoles. These cells are mostly devoid of organelles.