Ultrastructural aspects of the ovarian follicle and egg envelope of the sea-grass goby Zosterisessor ophiocephalus (Osteichthyes, Gobiidae)

The development of the ovarian follicle, the chorion, the attaching filamen ts apparatus, and the egg surface are described in the grass goby Zosterise ssor ophiocephalus by transmission and scanning electron microscopy. The fi rst appearance of the zona radiata externa is followed by the apposition of a canalicular lay er in the outer zona radiata interna, and then of a fibr ous tangential network in the inner zona radiata interna, reaching an overa ll thickness of 5.6 mum in mature eggs. Both zona radiata interns component s are likely secreted by the oocyte, whereas the apparently mucopolysacchar idic Zona radiata externa is produced early by flattened granulosa cells. D uring maturation. granulosa cells become cubic in cross section and elongat e from the animal pole, marked by the prospective micropyle and oriented al ong the oocyte meridians. Their cytoplasm is markedly engulfed with enlarge d cisternae of the rough endoplasmic reticulum involved, together with mito chondria and well-developed Golgi complexes. in adhesive filaments protein matrix secretion and the making of the basal plate. Filament matrix aggrega tes in the granulosa cells intercellular spaces, where it is confined by in tercellular junctions The basal plate is hollow in the centre surrounding t he micropylar pit and supports a cribriform column of netted filaments even tually fraying off and becoming the egg adhesive apparatus. The comparative functional and systematic relevance of these features among teleosts is di scussed and related to environmental and life style adaptations.