Systematic resolution of Crossobothrium Linton, 1889, and taxonomic information on four species allocated to that genus.

The systematic status of the tetraphyllidean genus Crossobothrium is resolved. The description of the type species Crossobothrium laciniatum is emended to include new information from light and electron microscopy. Orygmatobothrium dohrnii is transferred to Crossobothrium and its description is emended. Crossobothrium dohrnii n. comb. differs from C. laciniatum in the morphology of large microtriches on the distal bothridial surface, the presence of irregular papillose projections on the distal bothridial surface, the possession of irregular, incomplete loculi on the bothridial margin morphology, and exhibiting oblong testes. The genital pore position of C. dohrnii also differs from C. laciniatum. Species of Crossobothrium differ from species in other sampled tetraphyllidean genera in apical sucker tegumentary surface morphology. The 2 species differ from species in all tetraphyllidean genera in possessing a field of deep longitudinal muscles and a greater number of follicles in the vitelline field at the level of the ovary. Two species formerly allocated to Crossobothrium, Phyllobothrium filiforme, and Phyllobothrium triacis, are transferred to Paraorygmatobothrium, and their descriptions are emended. Three other species previously allocated to Crossobothrium, namely Orygmatobothrium angustum, Phyllobothrium squali, and Tetrabothrius longicolle, are considered incertae sedis. As a taxonomic entity, Crossobothrium has suffered from a case of mistaken identity with tetraphyllidean species consistent in morphology with the genus Paraorygmatobothrium.