• 貝かい — shell / shellfish
• 貝殻かいがら — seashell
• 貝類かいるい — shellfish category
• 巻貝まきがい — spiral shell
• 二枚貝にまいがい — bivalve
• 赤貝あかがい — ark shell

More examples ▼

• 貝細工かいざいく — shell craft
• ムール貝がい — mussel
• ほら貝がい — conch shell

“貝” originally represented a cowrie shell, which was widely used as money in ancient times. Because of this, 貝 appears in many kanji related to value, cost, and exchange — such as 買 (buy), 費 (expense), and 賞 (reward).