An account of the structure of plants naturally begins with the cell which is the proximate unit of organic structure. The elementary unit of plant structure, as of animal structure, is the cell. Faunistically, although not geographically, the Nearctic and Palaearctic areas must form the two subdivisions of one great unit, for which the  Holarctic region  is now the generally accepted term.
Definition: a subclass considered a phylum of the kingdom Protista in some classifications; includes holozoic or saprozoic flagellates.
Flagellates: Heterotrophic Protists With Flagella. Heterotrophic flagellates are also found in the following taxa : The flagellates are a grade of organisation. Traditionally, they are those protozoa which spend most of their existence moving or feeding with a small number of flagella.This type of organization is the most widespread among protists.Of the 60 lineages of protists identified among the eukaryotes, 27 satisfy the condition of being a protozoan flagellate.ukaryotic flagella are not the same as flagella of bacteria. They have an internal structure comprised of nine doublets of microtubules forming a cylinder around a central pair of microtubules. The peripheral doublets are linked to each other by proteins.