'Derived' is the correct term in biology for "specialised" or "advanced". It is used for groups which have evolved from a more basal group. A derived trait is a trait that is present in an organism, but was not in the last common ancestor of the group being considered. Simplicity is often secondarily derived. For example, no mitochondria in the anaerobic protist "Entamoeba histolytica" is a result of their secondary loss.