Hymenolepidid Cysticercoids in Hyalella azteca of Cooking Lake, Alberta: Life Cycles and Descriptions of Four New Species

Abstract

Hyalella azteca (Saussure, 1858) in Cooking Lake, Alberta, serve as intermediate hosts for 10 species of hymenolepidid cestodes. Life cycles of Fimbriaria fasciolaris (Pallas, 1781), Hymenolepis hopkinsi Schiller, 1951, H. tuvensis (Spassky and Spasskaja, 1960), and three new species, H. pusilla sp. n., H. spinocirrosa sp. n., and H. trombidacantha sp. n., have been completed in the laboratory. Cysticercoids produced in experimentally infected H. azteca from eggs of adult Wardium paraporale sp. n. in grebes were identical to cysticercoids recovered from naturally infected H. azteca. Only the cysticercoids of the remaining three species were recovered. This article covers part of a study designed to reveal the role played by Hyalella azteca (Saussure, 1858) in the circulation of helminths at Cooking Lake, Alberta. During these investigations, natural infections with hymenolepidid cysticercoids were encountered in H. azteca. Attempts to identify and determine the life cycles of these cestodes were made during the summers of 1967 and 1968. MATERIALS AND METHODS The materials and methods were modified only slightly from those described by Podesta and Holmes (1970). The cysticercoids are small and occur in large numbers in each infected amphipod. When the head of an infected amphipod was taken off, only a few cysticercoids were removed from the hemocoel for identification. The remainder of the cysticercoids, still within the body of the amphipod, were force-fed to ducks. The measurements and drawings of the cysticercoids were made on unfixed specimens mounted in tap water. Hook squashes were made in Aquamount. Adult specimens were stained in Semichon's acetocarmine or Delafield's or Ehrlich's hematoxylin and mounted in balsam. Drawings were made with the aid of a camera lucida and phase contrast microscopy. Unless stated otherwise, the descriptions are based on 20 specimens. Measurements are in microns unless otherwise stated. The range of measurements is given, followed by the average in parentheses. The types of structure of rostellar hooks and the types of location of genital glands are after Skrjabin and Mathevossian (1945).