When I got my axolotl a few years ago, she developed a lump on her belly. I was new to axolotls so I took her to an exotic vet (you've never had an experience with a vet until you've taken your pet to the vet in a bucket). She put her in a small tank and angled it to see. She said that my axi looked healthy, the lump wasn't inflammed and not to worry about it. My axolotl is albino, so it was easier to see that. Anyway, in a few months I thought it was going to grow into another leg, but one day it was gone! I think it just fell off. She has no mark where it was at all. I would suggest that you go to a vet to reassure yourself though.
