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. Recently, we have reported that there was a remarkable difference in motility initiation in vitro between micro and macro parasperms, that is, at the start of culture, all the micro parasperms have actively moved, while the macro parasperms have never shown any motion. After then, the fact was newly observed in some individuals that both micro and macro parasperms had actively moved at the start of culture. About these differential patterns of motility initiation were divided into two type, namely, the former is type A and the later is type B.
In present investigation, the motility initiation pattern of the macro parasperms was type A in individuals with well-developed testis in which almost all the eusperms were on the way of metamorphosis, indicating that the spermatogenesis is very active. In contrast, the motility initiation pattern was type B in individuals with underdeveloped testis in which almost all the eusperms have done metamorphosis. Furthermore, the motility activity of eusperm was very low in individuals which parasperm indicate the motility initiation pattern of type B. These findings indicated that the motility initiation pattern of parasperm is type A in the bleeding season of this species and it is important for reproductive advantage.