Ultrastructural observations on oogenesis and shell formation in Gyrinicola batrachiensis (Walton, 1929) (Nematoda: Oxyurida)

Abstract

SUMMARYIndividual females of Gyrinicola batrachiensis produce 2 types of eggs: thin-shelled auto-infective eggs are produced in the ventral horn of the reproductive tract and thick-shelled eggs (transmission agents) are produced in the dorsal horn. Fine structure of oogenesis and egg-shell formation in the 2 horns of the reproductive tract were studied and compared. Early stages of oogenesis were similar in both horns but mature oocytes differed considerably. Those in the dorsal horn were larger than those in the ventral horn; they contained large numbers of lipid droplets, peripheral patches of glycogen and several types of cytoplasmic granules presumably acting as yolk or playing a role in shell formation. Mature oocytes in the ventral horn contained large amounts of glycogen, relatively few lipid droplets and large multivesicular bodies. Four shell layers formed around ova in the dorsal horn: a vitelline layer, a lipid layer, a chitinous layer and an outer protein coat similar to that described in other oxyurids. Only the vitelline layer formed around thin-shelled eggs. Thick-shelled eggs did not embryonate in utero but thin-shelled eggs nearest the vagina contained larvae. The first moult in eggs of G. batrachiensis was described in a previous communication and it is suggested here that the thin fibrous layer loosely applied to the cuticle of infective larvae in thin-shelled eggs is the moulted 2nd-stage cuticle.