Ultrastructural studies on microfilariae (Nematoda: Filarioidea)

Abstract

The ultrastructural morphology of selected microfilariae from four genera is described and compared. 1. The sheath is composed of a thick layer of material not limited by membranes. 2. The cuticle is composed of a trilaminate membrane, a dense cortical layer and an inner fibrous layer. The outer leaflet of the trilaminate membrane is covered with a dense surface layer. 3. The hypodermis is formed of four components, and the outer membrane of each component is castellated. 4. Muscle cells are located in the four quadrants of the worm; each cell is divided into a contractile and a non-contractile region. Anterior muscle cells are probably involved in the movement of the hook. 5. A buccal capsule is situated at the anterior tip of the microfilaria; it is connected to the pharyngeal thead. The thread is already surrounded by the future oesophageal cells. It is not yet known whether these structures are functional in the microfilaria. 6. Three kinds of sensory organelle have been identified; they all contain modified cilia. The hook is associated with one of the amphids. 7. The excretory vesicle opens through a pore in the cuticle and is surrounded at its base by an elongate cell. The apparatus may possibly have an excretory, secretory or osmoregulatory function. 8. The inner body is composed of dense, granular material; it is already surrounded by the future intestinal cells. The inner body is thought to represent some kind of reserve material. 9. Apart from its size the G1cell shows no unusual characteristics. 10. The anal vesicle opens through a pore in the cuticle and is surrounded at its base by the three R cells. The anal apparatus may be instrumental in the removal of waste materials, or it may be involved in some secretory activity.