Opalina is a genus of parasitic heterokonts found in the intestines of frogs and toads.

They lack mouths and contractile vacuoles, they are covered with nearly equal flagelliform cilia, and they have numerous nuclei, all similar.

[1] All the species are obligate endosymbionts, most likely commensal rather than parasitic, in cold-blooded vertebrates.

They are saprozoic, consuming dead matter, which suggests their commensal role.

The body is flattened, leaf-like and oval in outline and covered by thin pellicle.