Flagella are structurally almost identical with the much smaller Cilia. So much so that it has been proposed protists bearing either should be unified in the Phylum "Undulipodia". Previously, Margulis had proposed that the Ciliates alone should be placed in a Phylum "Ciliophora". Admittedly, the Protista is a collection of disparate single-celled forms, but while a more sophisticated taxonomy is in flux (changing), Protista is still a useful term.