Studies On The Gonad Development And Fertilization Of The Nemertean Procephalothrix Simulus

The annual cycle of gonad development and the fertilization of the nemertean, Procephalothrix simulus, were studied by histological method.1. Gonad development: During July 15, 2005 to October 15, 2006, P. simulus were sampled monthly or semimonthly (in reproductive seasons) at Taiping Jiao, Qingdao, China. Specimens were examined by histological method to determine the cycle of the gonad development of this nemertean. The results showed that: The sex ratio (female: male) was about 1: 1. The sizes (body width and body weight) of mature males and females were not significantly different; females are rosy in colour and males are white, largely owing to the metamerically arranged gonads. Gonads, which were not detected in samples of autumn months, arose in December, but sexes were indistinguishable until middle January. Both ovaries and testes appeared mature on March 15, and disappeared on April 15. Then P. simulus immediately started another upgrowth stage of gonads. The gonad development of both sexes reached the maximum in June, and disappeared in September to October. These results suggested that P. simulus are likely to spawn twice a year, in the early spring and the early summer, respectively.2. The fertilization of Procephalothrix simulus: Sperm penetration occurred at the metaphase of the first meiosis of oocyte. About 30～35 min after insemination the first polar body was ejected and the second polar body was ejected about 10 min later. The female and male pronucleus formed and fused about 45～50 min after insemination. The first and the second cleavages finished about 60 and 80 min after insemination, respectively.