VARIATION IN THE EGG CELL FORMING REGION OF GYRODACTYLUS-KOBAYASHII HUKUDA, 1940 (MONOGENEA, GYRODACTYLIDAE)

The egg cell forming region of Gyrodactylus kobayashii from goldfish ( Carassius auratus) is a thin nucleated cytoplasmic layer surrounding t he developing egg cell (=oocyte). The cytoplasm contains numerous elon gate membranes, As parasites age, the egg cell forming region becomes electron lucent. The epical membrane of the egg cell forming region be comes disrupted in places, A basal matrix is indistinct in new-born an d young worms, becoming more evident as worms grow older. Numerous pit s (=basal pits) are found along the basal plasma membrane of worms wit h a mature male system. These pits appear to be stable components of t he membrane and resemble hemidesmosomes. Basal pits were co-incident w ith sperm in the egg cell forming region in 3 of 5 worms examined. The function of the basal pits of G. kobayashii could not be determined, It is postulated, however, that they either assist sperm to traverse t he egg cell forming region to fertilize the egg cell or stabilize the egg cell forming region against damage by sperm traversing this layer. The egg cell forming region encloses a large egg cell and 1 or more s maller differentiating egg cells. The ripening egg cell has a large nu cleus and extensive cytoplasm, The cell has a thickened membrane. Larg e vacuoles and invaginations at the periphery of the egg cell appear t o engulf cytoplasm of the egg cell forming region. (C) 1997 Australian Society for Parasitology.