Zooplankton

is the first organism next to Phytoplankton in the first cube. If Broth of Life is used, Zooplankton will evolve and Stromatolite will be born. Zooplankton will begin to spawn at 150,000 Phytoplankton.

Game issues
There is a known bug where the Zooplankton population will cap at 8,750 until several million phytoplankton or you load the campaign, which is unfortunate.