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.
The word phylum (plural: phyla) is a category used to classify marine organisms. In this article, you can learn the definition of phylum, how it is used, and examples of phyla used to categorize marine life.he word phylum (plural: phyla) is a category used to classify marine organisms. In this article, you can learn the definition of phylum, how it is used, and examples of phyla used to categorize marine life.