殻かく頂ちょう

noun

apex of a shell; umbo

Zoological term for the pointed tip or earliest part of a mollusk shell, often used in descriptions of bivalves and gastropods.

• 二に枚まい貝がいの殻かく頂ちょうは、成せい長ちょうの起き点てんとなる部ぶ分ぶんです。

  The umbo of a bivalve is the part that serves as the starting point of growth.

• この巻まき貝がいの殻かく頂ちょうは鋭するどく尖とがっている。

  The apex of this gastropod shell is sharply pointed.