I don't know specifically about the pom pom crab, but in general ocean critters have a planktonic stage that we can't keep alive in our tanks. They drift around and are delicate enough that touching stuff like pumps and filters damages them. They also need food that we don't have in our water. The list of critters that we can breed in our tanks (and we pay a lot for) is pretty short. If I could figure out how to raise shrimps that go for $25 at the store I sure would.