THE MORPHOLOGY AND LIFE-HISTORY OF THE DIGENETIC TREMATODE, AZYGIA SEBAGO WARD, 1910

¹ New York University, New York, N. Y., and The Marine Biological Laboratory, Woods Hole, Massachusetts

A chronological account of the genus Azygia discloses discordant observations and divergent opinions. Dawes (1946) recognized only a single species, A. lucii, in Europe. In it he included A. robusta Odhner, 1911, which reaches a length of 47 mm. and Ptychogonimus volgensis von Linstow, 1907, which measures 5 to 6 mm. in length and had been transferred to Azygia as a valid species by Odhner (1911). In America several species have been described, but there is no agreement on the number that are distinct and valid. In fact, there is no adequate information on the extent of variation that occurs in a natural species, and consequently on the features that can be relied on to distinguished between species. This situation is not peculiar to Azygia, but obtains in many genera. It is the natural result of development by members of a parasitic species in different hosts, invertebrate and vertebrate, often of different taxonomic groups, which differ in their nutritional and other physiological conditions, and accordingly influence the development and morphological features of the parasite. Until the life-cycle is known and the variation that normally occurs in each possible host is measured, the precise limits of specificity will remain uncertain. Comparison of specimens and descriptions indicates that A. lucii may be endemic in North America, that possibly it is distinct from A. longa (Leidy), that A. angusticauda (Stafford) is a valid species, and that the species described by Goldberger (1911) may be identical with A. sebago Ward. Information concerning the life-history of species in the genus Azygia is meager. Szidat (1932) showed that Cercaria mirabilis Braun is the larva of A. lucii. He described a second larva, Cercaria splendens, presumably another species of Azygia, but the adult stage remains unknown. Sillman (1953a) reported the life-cycle of a species that he identified as A. longa and the present paper presents data on the morphology and life-history of a species believed to be A. sebago. Stages in the cycle are described and figured.