Swamp leech - Helobdella stagnalis

Japanese: ヌマビル(沼蛭) - ヌマビル（英語表記）Helobdella stagnalis

An annelid of the family Glossiphonidae in the class Hirudinae. It is widely distributed throughout the world, and can be found in various parts of Japan. It inhabits ponds, swamps, and lakes, but prefers hard water (calcium carbonate _CaCO3 content of 60 mg/l or more) where food is abundant. The body is slightly elongated and ovoid, 6 to 12 mm long and about 4 mm wide, translucent grayish white, and has no spots or papillae, but has one yellowish-brown chitinous platelet in the center of the anterior dorsal surface. The anterior sucker is small, with a mouth at its base. The posterior sucker is large. It is hermaphroditic, with both the male and female genital openings opening at the 12th segment, but the male genital opening is located slightly forward.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

ヒル綱グロシフォニ科の環形動物。世界中に広く分布し，日本でも各地に見られる。池，沼，湖などに生息するが，とくに食物が豊富な硬水(炭酸カルシウムCaCO₃含量60mg/l以上)の場所を好む。体は，やや細長い卵形で体長6～12mm，体幅約4mm，灰白色の半透明で，斑紋や乳頭などはないが，前方の背面中央に1個の黄褐色のキチン質の小板をもっている。前吸盤は小さく，その底に口がある。後吸盤は大きい。雌雄同体で雄生殖口と雌生殖口はともに第12体節に開くが，雄生殖口がやや前方に位置する。

出典　株式会社平凡社世界大百科事典第２版について　情報

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