OPALINA (so named by J.E. Purkinjě and G. Valentin), a genus of Protozoa, without mouth or contractile vacuole, covered with nearly equal flagelliform cilia, and possessing numerous nuclei, all similar. It has been referred to Aspirotricha by Bütschli, but by M. Hartog (Cambridge Natural History, vol. ii., 1906) has been transferred to the Flagellates (q.v.). All the species are parasitic in cold-blooded Vertebrates.