Differentiation of cytoplasmic organelles and storage of yolk during vitellogenesis in Hemidiaptomus ingens and Mixodiaptomus kupelwieseri (Copepoda, Calanoida)

Abstract These investigations concern two freshwater calanoid copepods Hemidiaptomus ingens and Mixodiaptomus kupelwieseri . The first aspect of the research relates to the processes involved in the formation and the differentiation of the ooplasmic organelles at the time of primary vitellogenesis. During this phase, a number of complex associations develop in the ooplasm. They consist chiefly of nuage‐like structures, corresponding to extruded nuclear material, and vesicular formations, some arising from the nuclear envelope and the others neoformed in the ooplasm. These associations represent centers of maturation for ribosomes and synthesis for reticulum membranes. Annulate lamellae may be observed near these associations. Biogenesis of the reticulum always precedes the differentiation of the Golgi apparatus. Indeed, the dictyo‐somes develop in characteristic complexes including endoplasmic reticulum cisternae and numerous vesicles resulting from intensive blebbing from cisternae. The second aspect of this research concerns yolk synthesis and accumulation of hyaloplasmic inclusions. A preliminary synthesis of yolk occurs early in these complexes and becomes more important after achievement of Golgi apparatus biogenesis. However, the most important yolk storage results from exogenous molecules and consists of complex globules, which develop into the ooplasm during secondary vitellogenesis. Formation of these globules is associated with the accumulation of two categories of inclusions in the hyaloplasm, i.e., lipid droplets and clusters of glycogen particles. At the end of vitellogenesis, a new type of endogenous material develops into small cisternae localized in the cortical ooplasm. © 1993 Wiley‐Liss, Inc.