Germinal development in the sporocysts and rediae of the digenetic trematodes

Abstract

In the vertebrate-dwelling adults of the digenetic trematodes spermatogenesis and oogenesis are not fundamentally different from these processes in other metazoan groups. The fertilized ovum in the egg develops directly into the miracidium which contains in its body cavity a varying number of germinal cells. After entering the molluscan intermediate host the miracidium metamorphoses into the primary germinal sac, the mother sporocyst. In its body cavity the germinal cells multiply and develop into secondary germinal sacs which may be either rediae or daughter sporocysts. There may be one, two, or in a few cases even more generations of rediae, but only one generation of daughter sporocysts is present in those groups that have this type of secondary germinal sacs. In each generation there is multiplication of germinal cells in the body cavity of the germinal sacs. However, the number of embryos produced varies greatly in different trematode groups. Ever since Steenstrup in 1842 presented the theory of alternation of generations for the life cycle of the digenetic trematodes, the method of reproduction in the germinal sacs has been a subject of controversy. Steenstrup's view that this reproduction is an asexual process of internal budding was soon discarded by most workers because of the finding of specific reproductive cells. Grobben in 1882 first proposed the hypothesis that the alternation of generations in the digenetic trematodes is a heterogeny, and that the reproductive cells in the germinal sacs are true parthenogenetic ova. Later, several workers described and figured the for-1 A joint contribution from the

An ultrastructural study of reproduction in the parthenogenetic metacercariae of Cercaria margaritensis Ching, 1982 (Digenea: Gymnophallidae)

“…The undifferentiated cells could give rise to the germinal cells that, in turn, cleave to give rise to embryo cells. The same can be seen in developing rediae and daughter sporocysts (up to the point of brood sac development), when some cells in the undifferentiated central cell mass become specialized as germinal cells (the so called primary germinal cells) and begin to cleave (Cort, Ameel & Van der Woude, 1954 ;Galaktionov & Dobrovolskij, 1998).…”

“…In many digeneans that have rediae in their lifecycles, and in the majority of those having daughter sporocysts, embryo development from primary germinal cells is accompanied by the formation of a specialized reproductive organ known as the germinal mass (Cort et al 1954 ;Galaktionov & Dobrovolskij, 1998). Nothing structurally similar to the germinal masses of rediae and sporocysts was found in the M1 and M2 investigated in this study.…”

Parthenogenesis and asexual multiplication among parasitic platyhelminths

“…As a general rule, many of the more primitive digenean groups have a restricted capacity for germinal cell division with small numbers of discrete, totipotent cells being formed within each germinal sac. Cort et al (1954) described limited multiplication of the germinal cells in several amphistome digeneans and this would appear to be correlated with low cercarial outputs in this group. Paramphistomum cervi and Cotylophoron cotylophorum, for instance, have been calculated to produce as few as 180 and 225 cercariae respectively from a single miracidium (Bennett, 1936).…”

Studies on Egyptian Trematodes with Special Reference to the Heterophyids of Mammals. II. Embryonic Development of Heterophyes aequalis Looss

“…With few exceptions, rediae are of 2 types: those that produce additional generations of daughter rediae, and others that give rise only to cercariae. Cort et al (1948Cort et al ( , 1954 Although a number of cercariae of the pleurolophocercous and closely related types have been described, those for specific trematodes of the family Heterophyidae are few. Sonsino in 1892 described Cercaria pleurolophocerca from a freshwater snail in Egypt.…”

“…Observation of the formation of germinal material at 2 sites in the redia is not entirely new Cort et al (1948). have shown that germinal masses consisting of unicellular and multicellular components may occur in the lateral as well as posterior walls of the body cavity in the mother rediae of Notocotylus urbanensis and Psilostomum ondatrae.…”