ИСТИНА

Halichoanolaimus robustus is a peculiar predatory nematode. Its alimentary tract is characterized by a voluminous complicated stoma equipped with solid rhabdions, muscular pharynx and conspicuous brown blind intestine lacking rectum and anus. This species feeds on other nematodes swallowed whole. In our research we study stoma and gut ultrastructure. Buccal cavity (pharyngostoma) consists of two compartments, anterior cup-shaped chamber and posterior narrow cylindrical part. Walls of the anterior chamber are reinforced by six longitudinal rhabdions terminating posteriorly with small sharp teeth. Walls of the posterior chamber are made with three thick rhabdions. A prey nematode is evidently grasped by the teeth and then swallowed down into the pharynx lumen and intestine. Midgut cells may differ even on the same cross-section. In the anterior intestine, two cell types occur differing in that which function predominates, absorption or secretion. Cells of presumable predominating absorbing function possess a developed microvillar brush and abundant inclusions while the cells of presumable secretory function have sparse microvilli, many dictyosomes and many small vesicles. Absorbing cells outnumber the secretory cells in the medium region of the intestine. Intestine epithelium of the posterior region is made up of only absorbing cells containing numerous electron-dense inclusions. Lumen of the posterior midgut can be filled with undigested remnants including such well-identified parts as copulatory spicules or buccal armatures of the ingested preys. By absence of rectum and anus, these remnants can be stored there throughout the life of the predatory nematode. However, enterocytes of H. robustus do not differ principally from those of species with normal through alimentary tract, possibly because of the short life span.