title: Taxonomy and biology of Diplozoidae (monogenea).
Creators: name: A.-M. Rasheed, A.-R.
Publisher: name: University of Liverpool Repository
Year: 2023

description: The study is divided into two parts. The first considers the taxonomy of species of Diplozoidae in the British Isles and the world. The second investigates the biology of Diplozoon homoion in field and experimental conditions. As a result of an extensive literature survey, the distribution of species of Diplozoidae has been assessed. About 63 species were found on 78 species of fishes of the families Cyprinidae and three of Characidae. The species of parasites occurred in Asia, Europe and Africa but not in Australia or North and South America. The factors effecting this distribution were discussed. Critical taxonomic studies on British materials revealed that there are two species, D. paradoxum from Abramis brama distinguished especially by an invagination and a few ridges (deep folds) on the posterior parts of the adult stages, and, D. homoion from various species of Cyprinidae, including A. brama, with an absence of these two characters on the adults. A study of the morphology of all stages in the life cycle of D. homoion revealed that most of the characters currently used in systematic work on Diplozoidae showed great variation and were therefore unreliable. As a consequence, many species which have been described are synonyms. Proposals made by other authors for new genera, subgenera and subspecies of parasites are critically discussed with special reference to phylogeny. The genera Diplozoon, Eudiplozoon and Inusiatus are thought to be valid. The genus Neodiplozoon requires further investigation. All the other genera, subgenera and subspecies are considered invalid. The Diplozoidae probably originated from both Microcotylidae and Discocotylidae, with the genera Eudiplozoon and Inusiatus ancestral to the other members of the family. The life cycle of D. homoion from Llyn Tegid was studied experimentally under laboratory conditions. At water temperatures of 18o_21 oC, the life cycle took 1~-20 days from egg laying to formation of the gravid worm. The prevalence, relative density, mean intensity and intensity of infection of Rutilus rutilus with D. homoion from Llyn Tegid were investigated from September, 1982 to December, 1983 and in June and July 1984. Infections were almost constant on all male, female and unsexed fishes throughout the year. The level of infection of fishes of different fork lengths was also investigated. Infections were minimal in fishes less than 10 cm long, but increased progressively with increasing lengths up to 20 cm but declined thereafter. The distribution of adult D. hornoion on the gills of R. rutilus fJ...( from Llyn Tegid was also examined in relation toLserial number of Qt.ft ht l the gil¥; the side of the fish, tte inner and outer hernibranchs, the segment of the gill and the manner of attachment of the clamps to one or two consecutive primary lamellae. It was found that the adult parasites were randomly distributed in relation to the gills' structures except for a preference for attachment to the first 3 gills and to the dorsal segments of the gills. Two consecutive primary lamellae were used for attachment twice as often as attachment to a Single lamella. Season, sex and fork length of the fishes had no effect on the distribution of the parasites on the gills