Circumscription: Marine flagellates, almost all with plastids with chlorophylls a and c, with two flagella and one additional locomotor/feeding organelle, the haptonema. Some mixotrophic, one species exclusively heterotrophic. Many with inorganic (calcareous) scales (coccoliths). Some with polymorphic life cycles. Cytological organization similar in many respects to stramenopiles with chloroplasts, and they have been classified with that group by some. They lack the synapomorphy of stramenopiles, and at this time molecular evidence does not support derivation from that group. Ultrastructural identity: Mitochondria with tubular cristae. Dictyosomes present. Plastids with lamellae comprised of three thylakloids, no stigma; plastid in an extension of endoplasmic reticulum-the periplastidial endoplasmic reticulum. Haptonema with enclosed microtubules not in 9 + 2 arrangement. Two flagella, without hairs, scales, or other excrescences, with up to four major microtubular roots and some non-microtubular materials. Mitosis with spindle nucleating in cytoplasm and nuclear envelope breaking down. Synapomorphy: Tubulocristate flagellates with haptonema. Composition: Several hundred species, with some dispute as to the status of one subset, the Pavlovales.