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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 7572

Jean-Pierre Mignot; [Etude Ultrastructurale de la Pedogamie chez Actinophrys sol (Heliozoaire) III. Gametogenese, Fecondation, Enkystement]. Protistologica XVI(4):533-547, 1980

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Two types of cells which correspond to the male and female gametes have been observed by the electron microscope. The first can be recognised by the typical pseudopodium already noted by Belar (1923). In the second, a depressed cortical zone with a network of canalicules filled with tubules seems to constitute the complementary fertilization structures. Its differentiation appears prior to the fixation of the pseudopodial lobes on the female gamete. It is confirmed that these structures are operative in the first phases of plasmogamy. The karyogamy preceded by the flattening of each of the pronuclei on the faces which are going to make contact is achieved by fusion in the centrifugal direction of the two nuclear envelopes. The oocyst which accumulates osmiophilic granules, analogous to vitellin granules, has three concentric envelopes: a mucous ectocyst secreted by the young gamont, a mesocyst formed from silicified scales which develop at the start of the sexual process in the cortical vacuoles and are excreted at the end of plasmogamy, an endocyst of composite structure with in particular a stratum of fibres arranged like liquid crystals and secreted at the end of encystment by vesicles budding off perinuclear reticulum and golgi cisternae.