Answer:
Plankton
Step-by-step explanation:
Among the given organisms planktona are placed in the beginning of the aquatic food chain. Planktons are passively free floating on the surfce of on currents of water bodies. They are microscopic organisms. Planktons are of two types -phytoplankton and if they are tiny plants called phytoplanktons and if they are tiny animals called zooplanktons. Dinoflagellates and diatoms are the two classes of phytoplanktons. Copepods, rotifers, tintinnids, and larvaceans are zooplanktons.