Shizukugai (droplet shell) - Shizukugai (English spelling) Theora fragilis (= T. lubrica)

Japanese: シズクガイ(雫貝) - シズクガイ（英語表記）Theora fragilis(＝T.lubrica)

A bivalve mollusk of the family Paraprionospidae that is an indicator of pollution. The shell is long and oval, very thin, glassy and translucent, and the dead shell is white. It is about 20 mm long, 10 mm high and 4 mm wide. The front end is rounded and tapers toward the rear end. The apex of the shell is low and slightly tilted forward. The shell surface is smooth and shiny. The inner surface has a small interlocking below the apex, and the edge of the mantle membrane is deeply indented. It is distributed from southern Hokkaido to Kyushu, and is found in the intertidal zone of the bay to muddy bottoms at depths of about 50 m. Along with the sandworm Paraprionospio pinnata , it is highly resistant to oxygen deficiency and lives in the inner part of the bay where the water quality is the poorest.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

汚染の指標となるアサジガイ科の二枚貝。殻は長卵形で非常に薄く，ガラス様の半透明，死殻は白色。長さ20mm，高さ10mm，幅4mmくらい。前端は丸く，後端のほうへ細くなる。殻頂は低く，多少前方に寄る。殻表は平滑で光沢がある。内面は殻頂の下に小さいかみ合せがあり，外套（がいとう）膜の縁は深く湾入する。北海道南部から九州に分布し，湾内の潮間帯から水深50mくらいの泥底に分布する。ゴカイ類のヨツバネスピオParaprionospio pinnataとともに酸素の欠乏にたいへん強く，湾の奥のもっとも環境の悪い水質のところにすむ。

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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