The Colpodea are a class of ciliate protozoa, common in freshwater and soil habitats. The body cilia are typically uniform, and are supported by dikinetids of characteristic structure, with cilia on both kinetosomes. The mouth may be apical or ventral, with more or less prominent associated polykinetids. Many are asymmetrical, the cells twisting sideways and then untwisting again prior to division, which often takes place within cysts. Colpoda, a kidney-shaped ciliate common in organic rich conditions, is representative.
Most ciliates placed here were originally considered advanced trichostomes, on the assumption that they lacked true oral cilia. However the Bursariomorphida, large carnivorous ciliates whose oral cavity forms a deep anterior pocket, were considered heterotrichs because of their prominent oral polykinetids. The modern class was first defined by Small & Lynn in 1981, based mainly on the structure of the body kinetids.
Furthermore, it simplifies the complexity of interactions among the sets of transverse microtubular ribbons in the cortex of members of the COLPODEA (Lynn, 1976), and it ignores the more or less longitudinal orientation of the T1 set of transverse microtubules of the members of the LITOSTOMATEA (Lynn, 1991).
Finally, SSrRNA gene sequences strongly suggest that members of the classes COLPODEA and PLAGIOPYLEA (although being members of the same major clade) are not sister taxa (Fig.
Often, the classes LITOSTOMATEA, SPIROTRICHEA, and ARMOPHOREA are in one clade (Fig.
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