A light and electron microscope study of the hindgut of the herbivorous isopod, Dynamene bidentata (Crustacea: Peracarida).

Abstract

The tubular hindgut of the intertidal herbivorous isopod, Dynamene bidentata, consists of a long dorso-ventrally flattened anterior region, surrounded by a network of muscles, and a short muscular sphincter which grades into a pair of anal flaps. The monolayer of epithelial cells forming the wall of the hindgut appears to take no part in the production of digestive enzymes, food absorption, or glycogen and lipid storage. One function of the hindgut is to propel undigested food material, enclosed within a peritrophic membrane, to the sphincter and anal flaps where faecal pellets are formed and ejected. At the fine structural level lateral plasma membranes, often partially obliterated by microtubules, are visible. The basal plasma membrane of a typical epithelial cell is deeply infolded, associated with mitochondria, and pinocytotic. The apical plasma membrane is irregularly folded, engaged in pinocytosis, and often encloses subcuticular spaces containing an acid mucopolysaccharide substance. An intima, composed of a thin double-layered epicuticle, and a thick acid mucopolysaccharide-positive endocuticle, overlies the cells. The endocuticle may selectively bind substances to the apical plasma membrane before they are engulfed by pinocytosis. The cells resemble those of osmoregulatory organs and may help counterbalance changes in the haemolymph concentration resulting from the intertidal existence of this isopod.