Dark Ages

So, do I have the internal structure of an amphibian?

Yes.

And what are the benefits? Can I breathe underwater?

Depends. I decided to leave such details to the players' imagination. Well, in any case, the body temperature will be lowered, for example. Gills – I should say, not all amphibians have them, but I think that also fits the internal structure. You can. Well, not very effective (a weak trait), but you can.