Study On The Development Of Sex Gonad And Reproduction Cycle Of Marphysa Sanguinea

The germ cells' origin , morphological studies and development characteristics of Marphysa sanguinea , were examined by the histological section, light microscopy and the transmission electron microscopy. The yearly change of its reproductive cycle was also examined.Marphysa sanguinea 's male and female can be distinguished with our naked eyes during its maturing stage. The histological section suggests that Marphysa sanguinea has no definitive sex gonad and its germ cells originate from ventral coelomic epithelium . No nurse cells were found during its gametogenesis, and at an early stage in their development the nutriment comes from blood vessel near genesis location, and then from the coelomic fluid after dispersing into the coelom. The germ cells were successively produced except at the resting stage and were realeased in several times during maturing stage. The spermatogonia which derived from male germinal epithelium form syncytium after mitoses. With the development, the volume of the syncytium gradually enlarges and also the cells increase in quantity and volume. Primary spermatocyte , second spermatocyte and spermatid develop in the coelom as syncytium and separate from each other at the sperm stage. Dormal spermatogenesis is faster than the ventral spermatogenesis. The female germ cells don ' t form syncytium during their development. Oogonia adjacent to germinal epithelium have a high N/C ratio and deep nucleus stain. With the development, N/C ratio falls and the nucleus stain abates. At the same time a prominent nucleolus appears, cytoplasm become more and more, and the yolk granules and the lipid dropletsgradually add. Primary oocyte develops in the coelom.Ultrastructure studies shows Marphysa sanguinea ' s spermatozoon belongs to 'primitive type' and has flagellum. The longitudinal section of the mature spermatozoon shows that its head' s length is 3. 5 y m, in the front of the head is cap-like or cone-shaped acrosome and at the back of the head is the nucleus. The tail is 8-9 times as long as the head' s. The main structure of the tail is the axial filament which has "9+2" canal iculus structure. The cross-section of the back end of the head shows that there are six mitochondria and the distal centriole is perpendicular to the proximal centriole. At the syncytium stage the germ cells join together with the help of the cytoplasmic projections and the cytoplasmic bridge. The cells derive from the same syncytium keep the synchronization of their development. The lipid droplets and the cortical granules can be found inside the mature ootid, and the yolk granules density reaches the biggest. The membrane whose surface has microvilli is thick.According to the development of the germ cells and the proportion of different germ cells in the coelom , the sex gonad development of Marphysa sanguinea can be divided into the following five stages: proliferating and growing stage, pre-maturing stage, maturing stage, spawning stage, and resting stage. By observing the changes of sex gonad on histological sections, it is considered that the sex gonad development of Marphysa sanguinea has only one cycle in a year in Rushan area, Shandong Province. The proliferating and growing stage is from December to the next year' s April, pre-maturing stage from May to June, maturing stage from July to September, spawning stage from late July to September, resting stage from October to November and the reproduction peaks from July to August.