M.Sc. (Zoology) / The trilobic processes lateral on the cephalon were found not to be a constant feature and varied from well developed to nearly absent. A conical structure and minute openings on the dorsal surface of the antennae were found, as well as a number of small openings ventrally on the cephal on and abdomen. Mouthparts including the labrum, mandibles, maxillules and maxillae were described with the aid of electronmicrographs. An additional seta was found on the second leg, changing the original armature formula. All recorded host fishes infested by species of Mugilicola are estuarine fishes, and with the exception of two, the host fishes are mullets (Mugilidae). A diagnostic species compendium of the genus Mugilicola is presented, and is composed from available literature as well as additional information obtained from the study. The family Therodamasidae and genera are placed within the family Ergasilidae. Ecological data were obtained from five surveys conducted between January 1995 and January 1996. Mean intensity, abundance and prevalence were determined. The influence of the physical water quality parameters on AI. smithae were analyzed. Results showed no preference towards male or female host fishes. Mean intensity, abundance and prevalence showed no correlation to small changes in the physical parameters. Infested hosts were between 200 - 300mm in length and the lengths of the parasites varied throughout the year. There was no correlation between the above mentioned and seasons. From the results obtained it became clear that AI. smithae is a continious breeder. Histological studies were conducted on the alimentary canal. Results showed that the alimentary canal consists of three parts: a foregut, midgut and hindgut. The foregut is composed of the mouth and a chitinized oesophagus, terminating in a muscular bulbus. The midgut is composed of three regions: the anterior midgut with little differentiation in the epithelium cells, a middle zone with epithelium cells that vary greatly in size and shape, and a posterior region. A short chitinized hindgut opens into a dorsally situated anus.