Motile stages of some Apicomplexa (e.g., merozoites, sporozoites, tachyzoites, bradyzoites, cystozoites) possess a protrudable conoid, which possesses two preconoidal rings, but it is always absent in similar stages of the genera Plasmodium, Theileria, and Babesia. Besides the ductules of the rhoptries two single (conoidal) microtubules pass the inner of the conoid reaching until the apical cell membrane. Their function is not yet understood. It might be that they are phylogenetic remnants, since they have also been proven recently in non-apicomplexan protozoans such as the photoautotrophic species Chromera velia (lives in coral banks). This flagellated species has also a conoid, which, however, is open along the side (proximal to a groove) of the protruding flagellum.