Phenotypic and genomic characterization of Tylodelphys sp. metacercaria (Diesing 1850) (Trematoda: Diplostomidae) recovered from Lates niloticus (Linna

: Metacercaria of Tylodelphys sp. a member of the Diplostomidae, was isolated naturally from the gas bladder of Lates niloticus (Nile Perch), found in Lake Nasser (southern Egypt) . The morphology, ultrastructure, and genomic characterization were investigated and described. The main characteristics were shown by the light microscope and these were confirmed by the electron microscope. The examined fish were found to be infected with Tylodelphys sp., with prevalence of 86%, with the highest prevalence shown to be in summer (26%) and the lowest in winter (16%). Morphologically, by light and scanning electron microscopy, the parasite was found to be linguiform, where the fore body comprised most of the worm and the hind body was reduced to a small, conical, pointed end. The tegument was unarmed and smooth. A small oral and a large ventral sucker were detected. The body contained two types of papillae; a fine anterior and a coarse posterior one. The genetic analysis of Tylodephys sp. showed it was similar to those of the species of fish origin found in GenBank, and a description of a new Egyptian genotype (accession number MH367017) was provided. The morphotype detected was found to have about 99% genetic similarity in the 12S rRNA region with other helminthes. The obtained results support an evolutionary addition of the Egyptian species of Tylodelphys sp. aiding in its taxonomy and diagnosis.