Ultrastructure of the Buccal Cavity Region and Oesophagus of the Insect Parasitic Nematode, Heterorhabditis Bacteriophora1)

Abstract

The cheilostom of the buccal cavity of third stage infective juveniles of Heterorhabditis bacteriophora is supported by an invaginated body cuticle. The buccal ring constitutes the junction between the cheilostom and the prostom which is supported by arcade cells of hypodermal origin. The mesostom cuticle is surrounded by non-muscular tissues comprising the anteriormost region of the oesophagus. Posteriad, the metastom and telostom cuticle or rhabdions are underlain by two tiers of oesophageal muscles designated as M 1 and M2. The lumen of the triangular cylindroid buccal cavity is continuous with a triradiate lumen that extends through the narrow musculooesophageal tissues of the corpus and postcorpus and continues through an enlarged basal bulb. Radial cells have broad to narrow strands of myofilaments that make hemidesmosomal contacts with the lumen cuticle and outer membranes. Based on the location of muscle insertions on the cuticle of the stoma and midregions of the triradiate lumen of the oesophagus, radial cell muscles are apparently contractile. Whereas myofilaments of marginal cells attached to terminal arms of the cuticle and the outer membranes appear to be primarily, but not exclusively, supportive. Electron lucent granules are present in oesophageal glands that surround a corrugated valve in the basal bulb.