The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but in general shorter and present in much larger numbers, with a different pattern than flagella. Cilia occur in all members of the group (although the peculiar Suctoria only have them for part of the life-cycle) and are variously used in swimming, crawling, attachment, feeding, and sensation. Nevertheless, although not a general practice, some authors prefer to call "cilia" both eukaryotic cilia and flagella, reserving the term "flagella" to the bacterial structure. Anywise, the fundamental difference between multiciliate flagellates (e.g., hemimastigids, Stephanopogon, Multicilia, opalines) and ciliates is the presence of macronuclei in ciliates alone.