There are phytoplankton and zooplankton. There's a good trick for that. And then zooplankton is easy to remember because animals live in a zoo . Dinoflagellates Dinoflagellates are a very old and still very successful group of organisms. They have inhabited the world's ocean for over a billion years.
Most dinoflagellates are single celled autotrophs with two whiplike appendages called flagella.
Although one flagella moves the organism forward and the other lets it rotate, they still are easily classified as plankton because they can not move much. If there was a ripple in the water they would not be able to swim against its current. The flagella are best used for enabling the dinoflagellate to correct their orientation and vertical position, so they can photosynthsize as best as possible in the exisiting light. This is sometimes why filterfeeders are not safe to be eatten by humans. Diatoms Diatoms are biochemically more evolved to dinoflagellates and are therefore the dominate photosynthetic organism.