THE MORPHOLOGY, LIFE-HISTORY, AND SYSTEMATICS OF THE DIGENETIC TREMATODE, HOMALOMETRON PALLIDUM STAFFORD, 1904

¹ The American Museum of Natural History, New York 24, New York

The successive stages in the life-history of Homalometron pallidum, a parasite of Fundulus heteroclitus, described by Linton, 1901 and named by Stafford, 1904 have been discovered and identified. The asexual generations are in Hydrobia minuta and the metacercarial stages are encysted in Gemma gemma, H. minuta, and small polychaete annelids which serve as secondary intermediate and transfer hosts. Knowledge of larval as well as adult stages gives a better basis for determination of the evolution and systematics of the allocreadiid-leprocreadiid trematodes. The subfamily Homalometroninae contains marine, brackish-, and fresh-water species. Manter (1963) discussed the geographical dispersal of the group and the possible significance of present distribution for the phylogeny and evolution of the parasites and of their hosts. In his opinion, the subfamily illustrates an evolution from marine ancestors, through secondary-division hosts, to become parasites of fresh-water fishes. Results of the present investigation support his hypothesis.