Full Idea
The standard classification holds that 'animal' is a genus and 'rational' is a specific difference.
Gist of Idea
'Animal' is a genus and 'rational' is a specific difference
Source
David S. Oderberg (Real Essentialism [2007], 3.5)
Book Reference
Oderberg,David S.: 'Real Essentialism' [Routledge 2009], p.60
A Reaction
My understanding of 'difference' would take it down to the level of the individual, so the question is - which did Aristotle believe in. Not all commentators agree with Oderberg, and Wedin thinks the individual substance is paramount.