Umbonium

...A snail shell of the family Celastridae, common on the sandy bottom of inland seas (illustration). It is also called Kishago, Shitadami, or Zezegai. The shell is 1 cm high and 1.5 cm wide. The upper surface of the shell is shiny and has thin grooves along the length of the shell, but the lower surface is smooth and has reddish lime deposits in the center. The shell pattern varies from individual to individual, but most have a yellow background with black spots arranged in a faint pattern. The edge of the shell opening does not thicken even in adult shells, and the inside has a pearlescent luster. As it burrows into the sand, the edge of the mantle membrane at the front of the soft body becomes water tube-like, and it draws in water through it. ...

*Some of the terminology explanations that mention "Umbonium" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…内海の砂底に多いニシキウズガイ科の巻貝（イラスト）。キシャゴ，シタダミ，ゼゼガイなどともいう。殻の高さ1cm，太さ1.5cm。殻表の上側は光沢があり，巻きに従って細い溝があるが，下側はなめらかで，中央部に赤みのある石灰が沈着している。殻の模様は個体によって変異があるが，多くは黄色の地に黒斑がかすり状に並んでいる。殻口は成貝でもその縁が厚くならず，内面には真珠光沢がある。砂中に潜るので軟体の前方の外套（がいとう）膜縁が水管状となり，そこより水を吸いこむ。…

※「Umbonium」について言及している用語解説の一部を掲載しています。

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