Studies on the helminth fauna of Alaska. XLIV. Revision of Ogmogaster Jägerskiöld, 1891, with a description of O. pentalineatus sp. n. (Trematoda:Notocotylidae).

Discrepant conclusions in the literature concerning the specific distinction of the two species assigned to the genus Ogmogaster Jagerskiold, 1891, necessitated a reevaluation of the taxonomic characters used in separating these trematodes. Study of material from baleen whales from North Pacific waters and from baleen whales and lobodont pinnipeds from the southern hemisphere disclosed the existence of two species which can be distinguished by consistent differences in numbers of ventral ridges, ratio of length of cirrus sac to length of body, and by other morphological characters. Since the original description of 0. plicatus (Creplin, 1829) does not permit certain identification of the species, and since the description of O. plicatus by Jagerskiold (1891) is a composite, including data for two species, the latter is redescribed on the basis of specimens from baleen whales (Balaenoptera spp.) from northern waters. The description of 0. antarcticus Johnston, 1931, is emended to encompass the range of variation observed in specimens from baleen whales from both hemispheres and from pinnipeds from the Antarctic. In addition, 0. pentalineatus sp. n. is described from the gray whale, Eschrichtius gibbosus (Erxleben), from waters near St. Lawrence Island, in the Bering Sea. The latter is distinguished from its congeners by its small size, few ventral ridges (five), and by other morphological characters. Parasite-host relationships and other aspects of the biology of these trematodes are briefly discussed. Since 1937, following a period of exploitation during which its numbers were seriously reduced, the gray whale, Eschrichtius gibbosus (Erxleben), has been protected by international agreement. Although these mammals are taken occasionally in arctic waters by aboriginal methods, few have been available for scientific study. Largely because of these circumstances, the gray whale is one of the few species of baleen whales from which no helminths have been previously identified