All are either unicellular or colonial, and may be either autotrophic or heterotrophic . Most dinoflagellates are an important part of the phytoplankton , and contribute significantly to the food sources of filter feeding zooplankton and benthic organisms. Noctiluca sp., a dinoflagellate, from Halstead, 1965. Most Foraminiferans have calcareous tests, and may be very abundant in the plankton or in the benthos . Radiolarian, from VanCleave, 1924.
Radiolarians are also an important component of the phytoplankton , especially in warmer waters.