Copepod zooplankton and pond snails evolved 500+ million years ago. You can grow & observe these in a planted ecosystem tank, with no air pump and no filter, just calcium (shells) and silica beach sand, with some iron, oak driftwood (boil everything), and Java fern. The pond snails are breeding like crazy so I'm looking for a dwarf pea puffer or other creature that eats baby snails and can live in a planted ecosystem tank with no filtration or pump.