Morphology and ultrastructure of the excretory organs in larvae of Ischnura elegans Vander Linden (Zygoptera: Coenagrionidae)

The production of urine in larvae of Ischnura elegans involves both Malpighian tubules and transport epithelia in the ileum. In final instar larvae 12 groups of mainly 5 Malpighian tubules occur. They discharge their contents into the intestine just anterior to the sphincter which separates midgut and hindgut. The Malpighian tubules show neither in their morphology nor in their ultrastructure any clear differentiation into segments as is found in many other insects. The luminal side of the tubule cells has an elaborated microvillous border. The basal cell membrane shows infoldings. Many mitochondria, sometimes concentrated just beneath the microvilli, occur in the tubule cells. The ultrastructure of the cells suddenly changes anterior to the confluence into a common duct (also called bursa or receptacle). The microvillous border disappears and the cells, containing fewer mitochondria, are filled with numerous vesicles and are typical mucus cells. The ileum has two types of epithelia; one is thin, the other is much thicker and has the features of a transport epithelium. Apically the cell membrane is much infolded. The basal membrane has many infoldings closely related to mitochondria. The presence of such epithelia suggests that reabsorption of electrolytes from the fluid produced by the Malpighian tubules occurs here.