Here is the taxonomic hierarchy:
Domain
Kingdom
Subkingdom
Infrakingdom
Superphylum/Superdivision
Phylum/Division
Subphylum/Subdivision
Infraphylum/Infradivision
Superclass
Class
Subclass
Infraclass
Superorder
Order
Suborder
Infraorder
Superfamily
Family
Subfamily
Infrafamily
Genus
Species
Subspecies/Variety
Breed/Subvariety
Therefor, Breed and Subvariety are the most complex levels of
biological organization.