The systematics and life-cycles of the helminths of a local population of Gammarus lacustris in a eutrophic lake near Edmonton, Alberta, is reported as part of a larger study of the composition and seasonal dynamics of the helminth fauna of gammarids.A total of 12 species of helminths, including eight cestodes, one nematode and three acanthocephalans, were recovered. Of these, eleven were new host records, ten were assigned to an intermediate host species for the first time, and one, Hymenolepis albertensis sp.nov., was described for the first time.Adults of all twelve helminths were raised in experimentally infested birds and the life-cycles of five species (Lateriporus clerci, L. skrjabini, Hymenolepis albertensis sp.nov., Fimbriaria fasciolaris and Polymorphus marilis) were completed in the laboratory. The larvae are described, and the developmental period in the gammarids, prepatent period and life span of the adults are given for many of the helminths.The rate of development of the cysticercoids of Lateriporus skrjabini was shown to be directly related to the size of the gammarid and inversely related to the intensity of infestation.The proboscis-hook formula was not a good diagnostic character for the separation of the three acanthocephalans, Polymorphus contortus, P. marilis and P. paradoxus; however, the size of the largest hook and the structure of the cystacanth body-wall were good diagnostic characters.I am indebted to Dr J. C. Holmes for advice and encouragement at all stages of the study. I also wish to thank Drs S. Prudhoe and D. R. R. Burt for their editorial assistance, Mr L. Graham for many helpful suggestions and information on the natural definitive hosts of the species encountered, Mr R. Podesta for his laboratory assistance, and Miss E. D. Senio for caring for the ducklings during their first few days of life. The study was supported by the Francis F. Reeve Foundation Graduate Bursary, the Queen Elizabeth Education Scholarship Fund, by the Department of Zoology through a Teaching Assistantship, by a grant from the R. B. Miller Biological Station Fund and by an N.R.C. operating grant (A–1464) to Dr J. C. Holmes.
A multivariate “inv” hook formula for forests