plankton

Plankton are the beginning of the food chain, starting with small fish, keeps the food chain in the ocean in order. Then as the fish are larger it is beneficial to people as a food source. Plankton also provides oxygen in the ocean, and they can consume carbon dioxide and even bacteria. A diatom is a group of algea that is single-celled and a dinoflagellate is unicellular as well but with two flagellas.

Picture: http://arch.ced.berkeley.edu/hiddenecologies/wp-content/uploads/2006/06/diatom-hhss051009-no6-229.jpg

Diatom:

picture 2: http://microscopetalk.files.wordpress.com/2010/10/dinoflagellate_-ceratium.jpg

Dinoflagellates