The Life-history of a Commensal Copepod, Ostrincola koe, in Japanese Marine Bivalves

1. The morphological and ecological difference between the both sexes and the sex ratio are described. 2. The breeding begins in April and ends in November and the main spawning occurs from June to November. 3. The females in early summer are the largest in body length and the most prolific, each bearing an average of 15 eggs in a pair of ovisacs; the females in August and September, however, are the smallest and lay about 11 eggs. 4. The length of time required for a bred female to grow mature (to her first spawning) is about 27-28 days at water temperature of approximately 25-26℃. 5. The life span of females and males seems to be 1.5-2 months and less than one month respectively at water temperature of about 25-26℃. The over-wintering females probably live as long as 5-6 months; a few individuals of the males and the 5. copepodids sometimes occur during winter. 6. It is presumed that 5 generations occur in succession in a year.共生橈脚類Ostrincola koeの生活史の概略を報告した. 1. 雌雄の形態上,生態上の差異および性比について述べた. 2. 産卵期間は4月から11月であり,産卵の盛期は6月から11月である. 3. 初夏の産卵個体は最も大型で抱卵数も最大であり,8・9月には体長最小で,抱卵数も少ない. 4. 雌が産出された後,最初に抱卵する迄の期間は,水温25～26℃前後でほゞ27～28日である. 5. 短期世代の雌雄の寿命は水温25～26℃前後で普通夫々1ヶ月半乃至2ヶ月,および1ヶ月弱であり,越冬雌個体では5乃至6ヶ月と見られる. 6. 年間世代数は越冬世代を含めて5世代と推定される