I just noticed my new albino clawed frog is missing an "arm."?

So, I bought an albino clawed frog today. It is very small (like less than the size of a penny), and I have read that they grow to the size of your fist. So, I figure it is a juvenile. These are aquatic frogs, that live their entire life underwater (unlike common frogs). I picked this one because it was so... show more So, I bought an albino clawed frog today. It is very small (like less than the size of a penny), and I have read that they grow to the size of your fist. So, I figure it is a juvenile. These are aquatic frogs, that live their entire life underwater (unlike common frogs).

I picked this one because it was so feisty - it was swimming around really fast. Funny thing - it was swimming so fast that I didn't notice it was missing half of one arm until I got half way home from the store. Now, I wonder - is this an injury, and is it part of this young frog's life cycle/development? I don't know a lot about these frogs, but if they start out like tadpoles, is it possible the this young frogs arm is still in the process of forming?
Update: P.S. - the store won't take it back/exchange it unless it is dead. So, that's out! It seems healthy.
Update 2: It wasn't with any tank mates when I bought it - it was isolated in a small cup (like they sell bettas). So, I do not think it had exposure to another animal that would cause injury.
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