Excretory system of representatives from family Diplozoidae (Monogenea).

Diplozoons are representatives of blood-feeding ectoparasites from the family Diplozoidae (Polyopisthocotylea, Monogenea). Although these worms have been the subject of numerous taxonomical, phylogenetic, and ecological studies, the detailed study of their excretory system has remained relatively neglected. Our observations focused on the morphological and ultrastructural features of the excretory apparatus of four diplozoid species: Diplozoon paradoxum, Eudiplozoon nipponicum, Paradiplozoon bliccae, and Paradiplozoon homoion. Observations were obtained using two microscope methods: light microscopy, equipped with differential interference contrast (Nomarski DIC) and transmission electron microscopy (TEM). The ultrastructure of two basic compartments which forms the excretory apparatus, flame cells with filtration apparatus, and canal cells forming the protonephridial ducts is revealed in this study. A unique consecutive sequence of longitudinal semi-thin sections of the excretory pore of E. nipponicum is visualized there for the first time.

Ultrastructure of the digestive tract of Paradiplozoon homoion (Monogenea).

Paradiplozoon homoion is a representative of blood-feeding ectoparasites from the family Diplozoidae (Polyopisthocotylea, Monogenea). Although these worms have been the subject of numerous taxonomical, phylogenetic and ecological studies, the ultrastructure of the alimentary system and related structures, as well as the mechanisms of essential processes like fish blood digestion, remain mostly unknown. Our observation of P. homoion using a transmission electron microscopy (TEM) revealed two main types of digestive cells-U-shaped haematin cells and connecting syncytium. Particular structures such as mouth cavity with specialised receptors, two oval-shaped muscular buccal suckers, pharynx surrounded with the glandular cells, oesophagus, the intestinal caeca with intact erythrocytes in the lumen, the apical pinocytotic fibrous surface complex and haematin vesicles of U-shaped cells have been shown in detail. According to our results, the P. homoion is degrading the blood components predominantly intracellularly.