ULTRASTRUCTURE OF THE BUCCAL CAVITY REGION AND ESOPHAGUS OF THE INSECT PARASITIC NEMATODE, HETERORHABDITIS-BACTERIOPHORA

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 cheilost om and the prostom which is supported by arcade cells of hypodermal or igin. The mesostom cuticle is surrounded by non-muscular tissues compr ising the anteriormost region of the oesophagus. Posteriad, the metast om and telostom cuticle or rhabdions are underlain by two tiers of oes ophageal muscles designated as M1 and M2. The lumen of the triangular cylindroid buccal cavity is continuous with a triradiate lumen that ex tends through the narrow musculo-oesophageal 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 loc ation of muscle insertions on the cuticle of the stoma and midregions of the triradiate lumen of the oesophagus, radial cell muscles are app arently contractile. Whereas myofilaments of marginal cells attached t o terminal arms of the cuticle and the outer membranes appear to be pr imarily, but not exclusively, supportive. Electron lucent granules are present in oesophageal glands that surround a corrugated valve in the basal bulb.