my personal pick for most underrated animal is the european legless lizard, which i think is often taken to just look like a normal and rather plain snake, but if you're familiar with reptile anatomy at all it looks more like some sort of bizarre heraldic fantasy creature than basically anything else on earth
it's called the lateral groove and is literally a sort of seam in it's body that's always present:
I /think/ what's going on is that these evolved from something like alligator lizards, which have very rigid, slippery underbellies next to soft, stretchy skin on their sides (where their legs are situated), but now that they've evolved to be a "snake" and don't have legs that need to move around, that soft skin has decreased and turned into a weird little seam so they can move easier and don't have a big weak point in their sides. it's compensation to have nice smooth scales all over and a flexible size like a snake does, using the lizard anatomy they're working with (edit, just to clarify: it does stretch out and help with movement and such since their scales can't spread like a snake's can, I more mean that this is evolution's weird attempt to create that adaptation out of the place where the legs used to be)
basically it's the leg removal surgery scar evolution dealt them
