The mature Sipunculus nudus individuals were selected for parents on the 10th day of June, July and August,and the ratio of female and male was 5:1. Observations on its spawning habits, fecundity and changes of germ cells in body cavity after 20-day temporary rearing were made. The results showed that the Sipunculus nudus was dioecism and showed in vitro fertilization. Oocytes matured and spawned in batch. The spawning time of Sipunculus nudusis was not fixed, but night fecundity was higher than the day. The Sipunculus nudus spawned in cluster movement. The average fecundity of Sipunculus nudus was 3. 20 x 10 , 4.43 × 10 , 3.46 × 10 cell respectively in June, July and August. Cumulative number of eggs (x) with time change (y) equation was y = 0. 430 5χ 3 - 25. 971χ 2 + 503. 39χ - 582. 56(r2 R0. 982 0), y = 0. 583 3 x3 - 33. 942χ 2 + 659.04χ -712.43(R2 =0. 984 7) ,y = -0. 31χ 3 + 1.467 6x2 + 245. 11χ - 278. 22(R2 = 0. 994 3) respectively in June, July and August. Relative content of mature oocytes decreased 4. 8% , 9. 0% , 26.0%(P<0.01)- According to the results of germ cell changes, the postpartum Sipunculus nudus has better fecundity after spawning in June and July.%2011年6、7、8月每月10日,挑选9∶6为5∶1的性成熟光裸方格星虫(Sipunculus nudus)亲体,在水泥池中暂养20 d,观察其产卵习性、产卵量及其体腔中生殖细胞的变化.结果表明,光裸方格星虫雌雄异体、体外受精；卵母细胞分批成熟,分批产卵；产卵时间不固定,昼夜皆可产卵,但夜间产卵次数和产卵量均高于白天;大量产卵时集群游动；6、7、8月的雌光裸方格星虫平均产卵分别为:3.20×104、4.43×104、3.46×104 cell,平均受精率达98.3％；6、7、8月日累计产卵量y与时间x的变化方程分别为:y=0.430 5x3-25.971x2+503.39x- 582.56(R2=0.982 0)、y=0.583 3x3- 33.942x2+ 659.04x- 712.43( R2 =0.984 7)、y=-0.31x3+ 1.4676x2+ 245.11x-278.22(R2=0.994 3).6、7、8月成熟卵细胞相对百分含量分别降低4.8％、9.0％、26.0％(P＜0.01)；6、7月的光裸方格星虫产后具有较已的再繁殖能力.
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