Originally, there were two subsections in the Protist (a/k/a Protoctista) kingdom: the Phylum_Protozoa (the animal-like protists) and the Division_Algae (the plant-like protists). Both groups were previously members of the animal and plant kingdoms, respectively. When you study zoology and botany, these groups will be included in the review of the animal and plant kingdoms. Since the early days of the Protist kingdom in the 1800’s a few more groups have been added to the kingdom, including the fungus-like (slime_molds and water_molds) protists.
The Protozoa ("first animals") are the animal-like (heterotrophic, motile) Protists and are classified (in part) based upon their method of motility (such as cilia, pseudopods, and flagella). Representatives of this group are primarily unicellular or colonial.
Use pages 18-23 and 32-38 in the Photo Atlas as a reference for your review of the Protists. Recall that the authors of your Photo Atlas do not use the same exact method of classification as the authors of your textbook. Hence, the water molds and most algae are placed in the Protist group by your text authors, but not the Photo Atlas authors.
Dinoflagellates are almost exclusively motile and unicellular. Although these organisms are usually unicellular, a few colonial forms do exist. Their bodies are composed of interlocking cellulose plates that are reinforced with silicon. Most species have one long flagellum that lies in a longitudinal_groove. The groove is located in the girdle region of the body.
A few species (the zooxanthellae) are photosynthetic_symbionts in bodies of marine_invertebrates. This association helps build coral reefs. Some forms are heterotrophic.
Some species are causative agents of Red_Tide, such as Karenia_brevis (formerly Gymnodinium_breve, associated with the coast of Florida) and Gonyaulax (along the coast of New England). Most reproduce asexually by longitudinal_division. Their storage products are usually oils or polysaccharides.
This microslide of Peridinium shows the typical dinoflagellate body organization, which includes the girdle region that houses the flagellar (a/k/a longitudinal) groove.