This biological division contains the algal species Euglena and over 1,000 species of related algae; they are all unicellular (single-celled) and are mainly found in freshwater environments. They are all photosynthetic (though some are secondary heterotrophs) and they all contain chlorophylls a and b. A unique feature of this division is that they store the energy they produce from photosynthesis as paramylum, an unusual carbohydrate. Members of this division have a contractile vacuole and a single flagellum.