Is Piglet (Winnie the Pooh's BFF) a pig or an armadillo?

I've been debating this with my friends for twelve years... He used to be greyish-green in his literary illustrations. The ridges on his body resemble an armadillo's ridged back... and the constant fear thing is an armadillo's main trait, but all the Disney stuff has him pink and calls him pig. So which is it?