Opalinata

Abstract

The opalinids (Opalinidae: Genera Opalina, Cepedea, Protoopalina, Zelleriella, and Protozelleriella) are highly unusual protists with large cells, multiple flagella, and two to hundreds of nuclei. The name Opalina is derived from the iridescent appearance when light reflects on the delicately folded surface of the cells. Opalinids are found exclusively in the intestines of frogs and some other hosts. They form the group Slopalinida together with two related genera of intestinal flagellates, Karotomorpha and Proteromonas. The former is a tetrakont flagellate that inhabits the intestines of certain amphibians, while the latter possesses only two flagella and is found in a wider spectrum of vertebrate hosts. Both morphol- ogy and molecular data suggest that Karotomorpha is phylogenetically closer to the opalinids, although both flagellates were traditionally classified in a single family, Proteromonadidae. Molecular data have shown that yet another unusual gut protist is closely related to Slopalinida: The genus Blastocystis. Unlike its relatives, it bears no flagella and is usually observed in the form of spherical cells with huge vacuoles. It is quite common in the intestines of many vertebrates (including humans) and invertebrates. Together, these organisms form Opalinata, a diverse assemblage of variously modified unicellular eukaryotes.