My chihuahua puppy has 5 toes on one of his paws?

It's just like a extra toe for my puppy, it's just and ecsessive, extra, unneeded part of his body? Why though? I got him from a pet store, he had lived in a cage for the first three months of his life until I fell in love with him. The cage was so small he hasn't ran around AT ALL in his life and he had NEVER seen, touched or felt grass. he was taught to pee where he was standing and poop where he was standing. He was bad at avoiding corners, obstacles and walls as he had NO experience of what it was like to walk normal and naturally like any other dog would. The toe hasn't effected him at all. But will he be harmed by it later on in life? Do you think I should get it removed or not? See a vet, or leave it? Its really useless, luckily hasn't harmed my puppy. 

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