[Cytoarchitecture of the vitellaria of two monogenean species, parasites of the holocephalan fish Chimaera monstrosa L. with analysis of vitelline structure in the Neodermata].

The ultrastructural features of the vitelline follicles of ectoparasitic monogenean Chimaericola leptogaster Leuckart, 1830 (Polyopisthocotylidea, Chimaericolidae) and endoparasitic Calicotyle affinis Scott, 1911 (Monopisthocotylidea, Monocotylidae), parasites of the gills and cloaca of a holocephalan fish, Chimaera monstrosa L., are described. The vitelline follicles of the studied monogenean species are composed of the cells of a single type, vitellocytes at various stages of development. Special isolation of the vitellarium from the surrounding tissue in C. leptogaster is absent. Instead, a close relationship between bordering vitelline cells and intestinal cells of numerous branches of the caecum diverticula is observed. However, vitelline follicles of C. affinis are enclosed in a thin fibrous sheath. Some differences in the composition of the vitelline material in mature vitellocytes of C. leptogaster and C. affinis are revealed, these include the presence of different number of vitelline globules within a cluster, up to 30 globules in C. leptogaster cluster and up to 50 globules in C. affinis, and the presence of moderately electron-dense homogeneous lipid droplets in C. affinis and heterogeneous droplets in C. leptogaster. The mature vitelline cells of C. leptogaster are recognised by the presence of clusters with granular bodies inside them, these bodies have the same size as vitelline globules. In developing vitellocytes of C. affinis, the glycan vesicles about 3.5 μm in diameter are present; in mature vitellocytes, these vesicles are destructed; this process is accompanied by liberation of glycogen rosettes and agglomerate of the dark material. Morphological variations of vitelline cytoarchitecture in the Neodermata are discussed.