Ultrastructural features of the body wall of the helminth Heterakis dispar (Schrank, 1790) (Nematoda, Heterakidae)

Abstract

The structure of the body wall (cuticle, hypoderm, and muscle layer) of the nematode Heterakis dispar (Schrank, 1790) from the family Heterakidae was studied using light and electron microscopy methods and compared with other species of the same family. The cuticle of the adult nematode H. dispar consists of 8 layers: 1 - an outer membrane layer or epicuticle; 2, 3 - outer and inner cortical layers; 4, 5 - outer and inner homogeneous or middle layers; 6, 7 - outer and inner fibrous or fibrillar layers; 8 - basement membrane. The cortical, homogeneous and fibrillary layers constitute 12.4, 45.3 and 42.3% of the all cuticle, respectively. The homogeneous layer of the cuticle in the lateral ridges in both male and female and near the bursa of the male is several times as thick as other parts of the helminth cuticle. Unlike other species of the family, males of H. dispar possess 3 different forms of cuticular structure in different parts of the body. In the basal layer of the cuticle, sustaining structures consisting of dense fibrils and microtubules were found, which were not previously noted in other species of the family. It is likely that they provide strength to the body wall of the helminth. In the hypodermis of the nematode, dorsal, ventral, and 2 lateral ridges are traced, the lateral ridges being twice as large as others. Ultrastructural features of the excretory channels and nerve cords located in the hypodermal ridges, were also revealed. The nervous system of the helminth is orthogonal. The ventral nerve cord is wider than the dorsal one. Muscle layer is of the polymyar type, number of muscle cells arranged in groups varies from 17 to 26, depending on the sex and body part of the helminth.