Dinoflagellates are tiny, one-celled organisms that live in oceans and freshwater ponds, rivers, and streams. Some dinoflagellates are like plants, depending on sunlight and basic nutrients for growth. Others are like animals, eating bacteria and microscopic organisms. They are part of a large group of diverse organisms that have been classified as "protoctists."

Size: microscopic to 2 millimeters
Habitat: oceans, freshwater ponds, rivers, and streams throughout most of the world
What they can do: make food from the Sun's energy; flash light through bioluminescence
Characteristics: some have protective, plate-like shells; swim in a spiral; can cause water to look golden or red

Image credits: main image: courtesy of Susan Carty.