The role of marine amphipods in the life cycles of the cestode genus Microsomacanthus at Bering Sea coast of Chukchi Peninsula. First results of the investigation

Investigation of the helminth fauna was carried out in different amphipode species at Bering Sea coast of Chukchi Peninsula in July-September 2004. More than 3700 amphipode specimens of the following three species were examined: Lagunogammarus setosus Dementieva, 1931 (n = 2772 specimens) (Gammaridae), Eogammarus barbatus Tzvetkova, 1965 (n = 471), and Spinulogammarus subcarinatus (Bate, 1862) (n = 509) (Anisogammaridae). Numerous metacestodes of four hymenolepidid species from the genus Microsomacanthus Lopez-Neyra, 1945 were found, namely gull parasites M. ductilis (Linton, 1927) and M. lari (Yamaguti, 1940) comb. n., and eider parasites M. minimus Ryjikov, 1965 and M. somateriae Ryjikov, 1965. Relative selectivity of cestodes in the choice of intermediate host is revealed: M. ductilis and M. somateriae are found on L. setosus only, while M. minimus and M. lari are found in both species of anisogammarids. Brief descriptions and figures of metacestodes are given; data on extensiveness and intensity of the intermediate hosts invasion in six collection localities are provided. The greatest extensiveness of invasion is recorded in L. setosus (E. I. in M. ductilis was 1.98 %, in M. somateriae - 1.84 %). The identification of metacestodes is confirmed by the finding of mature cestodes of all above species in two Pacific eider specimens (Somateria mollissima var. nigrum) and three gull specimens (one Larus argentatus and two L. hyperboreus) captured in the area where the largest sample of Gammaridae was collected.