Where does “毛蟹” come from?

毛蟹 (Japanese) comes from Japanese 毛, from Middle Chinese 毛.

毛蟹 (Japanese): a horsehair crab

Definitions

Step	Language	Word	Meaning
1	Japanese	毛	hair, fur; a kind of unit
2	Middle Chinese	毛	—

毛蟹 — Etymology, Origin & Word History | Etymology Explorer