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.
Difference between Prokaryotic and Eukaryotic Flagella. Flagella and Cilia are fine vibratile hair like membrane covered protoplasmic outgrowths that occur on the free surface of the cells and take part in producing a current in fluid medium for passage of materials and locomotion. Flagella are longer but fewer(generally 1-4). Flagella occur in group flagellate or protozoan protistans, euglenoids, dinoflagellates, choanocytes of sponges, gastrodermal cells of coelenterates, sperms of animal bryophytes and several pteridophytes, zoospores and gametes of several algae and primitive fungi.