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Opalinida(ō'pəlĭn`ĭdə), phylum of unicellular heterotrophic organisms of the kingdom ProtistaProtista
, in the five-kingdom system of classification, a kingdom comprising a variety of unicellular and some simple multinuclear and multicellular eukaryotic organisms.
..... Click the link for more information. . The opalinids are all intestinal parasites of small vertebrates, such as frogs, toads, and fish. Opalinid cells are covered with either short, hairlike structures called cilia or with longer flagella. Each organism has at least two nuclei. Their evolutionary lineage is unknown.
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