Generation of two types of spermatozoa, eusperm and parasperm is a common feature in most Prosobranch snails. In addition, Cipangopaludina Japonica produces two different sized parasperms, micro and macro parasperm. The eusperm is a uniflagellate cell with a normal haploid nucleus, participating directly in fertilization. In contrast, the parasperm is a multiflagellate cell with a small amount of DNA in the head, and does not genetically contribute to fertilization.
In present study, the in vitro motility initiation of parasperm has been temporally investigated. There was a remarkable difference in the motility between micro and macro parasperms. At the start of culture, all the micro parasperms have actively moved, while the macro parasperms have never shown any motion. After ward, the micro parasperms gradually began to stop the motion. Since several hours had passed after the preparation of sperm suspension, some population of micro parasperms stopped the motion and macro parasperms began to move. This fact suggests that macro parasperms of Cipangopaludina Japonica acquire the motile capacity after they were discharged from the testis.
The number of flagella in the parasperms from three males which were different from each other was examined on the motility of macro parasperms, resulting that there was no correlation between the number of flagella and the time for the motility initiation in macro parasperms.