mussels, various shellfish
蚍 centers on shellfish, especially mussels and similar bivalves. The meanings are closely related, covering various shellfish as a category.
蚍 combines 虫 (insect/creature) with 比, which likely contributes the sound. The character is used for shellfish, though the exact historical development is uncertain.
The insect radical 虫 often appears in characters for small creatures, including shellfish. The right side 比 suggests a pair, like the two shells of a mussel. Picture a mussel with its two shells side by side, labeled with the insect-like creature radical.
For ヒ, imagine a mussel making a soft 'hee' sound as it opens its shell: hee -> ヒ.