INVESTIGATIONS OF THE LIFE CYCLE OF POLYPODIUM HYDRIFORME USSOV (COELENTERATA), A PARASITE OF THE EGGS OF ACIPENSERIDAE

Abstract

This chapter highlights the investigations of the life cycle of Polypodium hydriforme ussov (coelenterata), a parasite of the eggs of acipenseridae. Polypodium hydriforme has been found within the oocytes of several species of Acipenseridae in the Volga, other rivers in East Europe, and also in the Amur. The sterlet proved to be the most infected host. Each maturation stage of the fish ovaria corresponds to a definite stage of the parasite development. The earliest known stage of Polypodium is a binuclear cell, with a large polyploid nucleus and a small haploid one, which inhabits young yolkless sterlet oocytes. While the oocyte grows, the large nucleus forms a deep cavity and surrounds the small nucleus, with a portion of cytoplasm. The small cell thus formed gives rise to the blastomeres of the future embryo, while the large nucleus, with the main portion of the cytoplasm, forms a capsule surrounding the parasite. The large hollow nucleus of the capsule fragments later into many polymorphic nuclei.