The microscopic floating population of plants in the ocean are called phytoplankton.
Diatoms are the dominant species of phytoplankton and are a major component in the food web.
The example below shows several different examples of the two types of diatoms. Out at the edges of the image can be seen more narrow or pennate diatom examples. This slide was produced in the 19th. Century by pushing individual diatoms into the pattern shown using a single-haired brush. Then the specimens were mounted under a cover glass.