Julia japonica is a species of a sea snail with a shell comprising two separate hinged pieces or valves. It is a marine gastropod mollusk in the family Juliidae.
The type locality for this species is Wakayama, Honshà «, Japan.
It eats green alga Microdictyon japonicum.
Its shell was also found in the intestine of fish Pacific yellowtail emperor (Lethrinus atkinsoni).