I'm no biologist and can't answer your first question. But can tell you that it's definitely edible. The English have Black Pudding, the Spanish have Morcilla; both 'blood suasage' types I've eaten. They were tasty with a slightly soft unusual texture.
Looking here : https://en.wikipedia.org/wiki/Black_pudding - it turns out that it's common all across the world. over 5 years ago