Crithidia brevicula is a species of parasitic flagellate protist belonging to the family Trypanosomatidae.

Other one-host trypanosomatids from hemipteran and dipteran insects have been traditionally placed in the same genus or others like Wallaceina, Blastocrithidia, Leptomonas, Herpetomonas, and Rhynchoidomonas.

[3][4] Wallaceina was characterized by endomastigote morphological forms, whereas epimastigotes and opisthomastigotes were features of the genera Blastocrithidia and Herpetomonas, respectively.

[4] Later comparison and phylogenetic analysis of 18S ribosomal RNA and glycosomal glyceraldehyde-3-phosphatedehydrogenase sequences of trypanosomatid taxa revealed that Wallaceina is polyphyletic.

[1] Wallaceina was a taxonomic patronym honoring the protistologist Franklin G. Wallace, a pioneer in the modern taxonomy of trypanosomatids.