Ultrastructural studies on vitellocytes of Allostoma sp (Prolecithophora, Plathelminthes)

The general organization of the vitellocytes in Allostoma sp. is described. In all the species of prolecithophorans studied, and therefore also in All ostoma sp., the eggshell globules have the same ultrastructure consisting o f highly electron-dense granules embedded in a medium-electron-lucent grey matrix (multigranular pattern) and mainly contain polyphenols. The type of yolk bodies principally characterized by membrane whirls in Allostoma sp. i s unknown for the other neoophoran taxa. This peculiar yolk originates from Golgi-derived vesicles, presumably containing lysosomal enzymes, which fus e with membrane-bound substrates. This characteristic is hypothesized as an autapomorphy of the Prolecithophora.