oyster
蠙 centers on the oyster, a shellfish that produces pearls. The meaning is specific to this mollusk.
蠙 combines 虫 (insect/creature) with 賓, which likely contributes the sound. The character specifically refers to the oyster, a type of shellfish.
The insect radical 虫 on the left suggests a small creature, and the right side 賓 looks like a guest under a roof with a shell (貝). Picture an oyster as a guest creature hiding a pearl inside its shell.
For ヘン, imagine a hen pecking at an oyster shell to get the pearl inside: hen -> ヘン, and the oyster is the creature with the treasure.