These holes are used to discharge excrement, eggs and sperm as well as water inhaled into the mantle in the process of branchial respiration, and the number of the holes is always within a certain range as the oldest hole becomes clogged up as a new hole is created during the growth of the shell.
この穴はえら呼吸のために外套膜に吸い込んだ水や排泄物、卵や精子を放出するためのものであるが、殻の成長に従って順次形成された穴は古いものからふさがっていき、常に一定の範囲の数の穴が開いている。