The depth of the photic zone may very depending on the clarity of the water. Some of the larva found in the plankton do not spend their entire life living in the plankton, this type of plankton is called meroplankton. For example as larval stage of fish cannot swim against the water currents but the adult fish can.
Diatoms are unicellular phytoplankton which have cell walls that are made of silica.
Dinoflagellates are also unicellular organisms, but dinoflagellates are also able to ingest food particles as well as use chlorophyll for photosynthesis. Dinoflagellates have cell walls that are made out of cellulose. Prior to 1974 gelatinous zooplankton was considered to be a relatively small and hard to sample contributor to the marine economy, so it was never studied in depth. In 1974 William Hamner used scuba gear to personally go into the water to observe and collect the organisms there. He found that gelatinous zooplankton was as abundant as crustaceans.