Theory:SJA television discontinuity and plot holes/The Nightmare Man


 * The Raxacoricofallapatorian is credited as a Slitheen family member, but has a few differences. The colour of the skin is a darker green, and the colour also covers the stomach, where as a Slitheen's fades. The fingernails were also green at one point.
 * Different members of the same species can have varying phenotypes/appearances, just like humans. There isn't any reason why all members would look exactly the same.