Proteins differ from one another primarily in their sequence of amino acids
In the Scientific name, first word represents "Genus" and as they are same it indicates that their Genus are same
Hope this helps!
The function of the limb is to help them get around and move. They might be similar in the way they’re structured? I don’t have a picture so I can’t tell. And you can assume that at one point these four animals all shared a common ancestor. Hope I helped!