Chiton (Stone Turtle Shell) - Chiton

Japanese: ヒザラガイ(石鼈貝) - ヒザラガイ

A general term for Polyplacophora mollusks, or one of the species in the Polyplacophoridae family. There are about 800 extant species of Polyplacophora, mostly found in Australia. About 100 species are found in Japan. The etymological name "chiton" means "knee shell," as it has eight shells lined up front and back on its back, and when removed from the rock it curves ventrally in a circular shape resembling a bent knee. Because of this position, it is also known by the names jiigase (old man's back) and kogoma (bent-back). The body is oval and thin dorsally and slightly bulging dorsally.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

多板綱の軟体動物の総称，またはその中のクサズリヒザラガイ科の1種を指す。ヒザラガイ類Polyplacophoraは現生は約800種でオーストラリアに多い。日本産は約100種。ヒザラガイの名は語源的には膝皿貝の意で，背面に前後にならぶ8枚の殻があり，これを岩から離すと腹側にまるく曲がるのがひざを曲げた状態に似るからである。その状態からまたジイガセ(爺ガ背)，コゴマリ(屈まり)の別名もある。体は楕円形で背腹に薄くて背側が多少膨らむ。

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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