Ultrastructure of the midgut epithelium of Wirenia argentea (Mollusca: Solenogastres)

Abstract

The midgut epithelium of Wirenia argentea Odhner is composed of two cell types: dorsal ciliary cells and digestive cells. Ciliary cells bear simple locomotory cilia with a pair of rootlets and without an accessory centriole. Digestive cells are the site of intracellular digestion and are characterized by an extensive endosomal and lysosomal system. The midgut epithelium shows a plasticity in digestive cell size and contents, depending on the amount of absorbed food material. Additionally, digestive cells produce membrane-bound mineralized granules as well as glandular vesicles, which most probably contain extracellular digestive enzymes. Four stages within the digestive cycle are defined. Cell types and cell cycles are compared with those known for digestive epithelia of other molluscs.