Heterokont

Circumscription: A major assemblage of tubulocristate protists, including taxa with and without chloroplasts. Plastids if present with chlorophylls a and c. Most flagellated taxa with one short and one long flagellum but some with only one flagellum. The long flagellum usually carrying tripartite tubular hairs that reverse the thrust from the flagellum. In a few cells the hairs are absent and in one lineage they may be attached to the body surface. Cells may also be aflagellated, amoeboid, or mycelial, may be extremely large (some brown algal kelps). Cells may have scales, organic walls, or inorganic walls. Includes parasites, saprophytes, autotrophs, and heterotrophs; includes some taxa with great species diversity (e.g., diatoms). Ultrastructural identity: This group has considerable diversity, with few features common to all species. Mitochondria have tubular cristae, usually with two flagella but one group of lineages have a single flagellum, and another lineage has many flagella arranged in rows (kinetics). if two basal bodies are present, they are typically anchored by four microtubular roots. Plastids are present in many species, with three thylakoids per lamellae and with a stigma usually included within the plastid. Dictyosomes present. Extrusomes may be present or absent. Mitosis typically with fragmenting membrane and microtubules arising from external to the nucleus, most usually from the bases of the flagella. Synapomorphy: Tubulocristate protists with tripartite tubular hairs, but there has been secondary loss of this character in some subsets.