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.
Phylum Mastigophora: These protists move with a whip like extension.called a flagella. The flagella is a long fibril that is spirally wound and beats or rotates in the water to move the protozoan about. Included in this group is the Peranema (shown at left), the Euglena and the Volvox.Click on the image to see more.hylum Mastigophora: These protists move with a whip like extension.called a flagella. The flagella is a long fibril that is spirally wound and beats or rotates in the water to move the protozoan about. Included in this group is the Peranema (shown at left), the Euglena and the Volvox.