Comparative studies on the histology of the ovotestis in Hypselodoris tricolor and Godiva banyulensis (Gastropoda, Opisthobranchia), with special reference to yolk formation

Abstract

The histology of the ovotestis was studied by light and electron microscopy in two nudibranch gastropod species. While in Hypselodoris tricolor the ovotestis is intimately associated with the digestive gland tissue, the large gonadal mass of Godiva banyulensis is placed freely in the haemocoele. This fact results in great histological differences between both species. As is common among Mollusca, the immature yolk granule in Hypselodoris and Godiva presumably originates from membrane-rich cytoplasmic inclusions, which we have termed dense multivesicular bodies. Such inclusions consist of an outer membrane enclosing membrane remnants and a granular, electron-dense material. These elements are accumulated and mixed in the center of the dense multivesicular body and could be actually transformed into the paracrystalline core of the immature yolk granule, the cortex of which is made up of part of the central accumulation materials that have not spread into the crystal. During vitellogenesis, some mitochondria are subjected to a process of transformation affecting mainly their inner membrane (including mitochondrial cristae) and matrix. However, the conversion of modified mitochondria into yolk precursors, as reported for other gastropod species, could not be determined with absolute certainty on the basis of our observations on static material. The mature yolk granule consists of a central paracrystalline core, similar in structure to that of the immature yolk granule, and a peripheral membranous cortex, which seems to spread centripetally, thus permitting the crystal to grow. The cortical material consumed in synthesizing the central core appears to be restored by addition of degenerative mitochondria to the yolk granule surface.

Ultrastructure of the ovary and oogenesis in six species of patellid limpets (Gastropoda: Patellogastropoda) from South Africa

“…Evidence of incorporation of exogenous yolk precursors through endocytosis in mollusc oocytes has not been widely documented (Jong-Brink et al 1983;Eckelbarger & Blades-Eckelbarger 1989), although it has been reported in one opisthobranch (Eckelbarger & Blades-Eckelbarger 1989), some cephalopods (Selman & Wallace 1978), pulmonates (Hill & Bowen 1976Bottke et al 1982;Jong-Brink et al 1983;Khan & Saleuddin 1983;Bottke 1986), two caenogastropods (Bottke 1973;West 19Sl), and a neritid (Eckelbarger & Young 1997). In contrast, autosynthetic yolk formation has been widely reported and is viewed as the primary yolk-forming process in the Mollusca (Jong-Brink et al 1983;Medina et al 1986).…”

Phylogeny of the Nudibranchia

“…This state is considered to be plesiomorphic. But in many nudibranchs, the gonad spreads over the digestive gland dorsally and is more or less strongly connected to it (Medina et al, 1986). In some genera (e.g.…”

Ultrastructural studies of spermatogenesis in Antalis entalis (Scaphopoda, Mollusca)

“…In bivalves, both single and multiple Golgi complexes occur, for example, a single Golgi complex has been described in Laternula limicola (Kubo 1977), Neotrigonia (Healy 1989), Musculus discors, Nucula sulcata, Dreissena polymorpha (Franzen 1983), Donax (Hodgson et al 1990) and multiple ones in Mytilus edulis (Longo & Dornfeld 1967), Spisula solidissima (Longo & Anderson 1969) and galeommatoid bivalves (Eckelbarger et al 1990). In mollusc classes with modified spermatozoa, for example, Opisthobranchia (Eckelbarger & Eyster 1981;Kubo & Ishikawa 1981;Medina et al 1985), Pulmonata (Takaichi & Dan 1977) and Cephalopoda (Maxwell 1974(Maxwell , 1975, only multiple Golgi complexes occur. Our studies of spermatogenesis in A. entalis provide confirmation of the primitive phylogenetic position of the Scaphopoda.…”