Members of the monerans and protist families are the simplest organisms. Individuals are much too small to be seen without a microscope.
Monera is a unicellular organism, they have a prokaryotic cellular organization, which means they lack well-defined, membrane-bounded organelles and nucleus. On the other hand, Protista is also unicellular organisms, but consist of eukaryotic cellular organization and well defined, membrane-bounded organelles and nucleus.
All forms of life on earth are divided into five categories on the support of the nutrition and energy they obtain, kind of cell (single cell or multi-celled), structural complexity, etc. These five kingdoms are Monera, Protists, Fungi, Plantae, and Animalia. Monera is the most primitive types of organisms which include blue-green algae (cyanobacteria), eubacteria and archaebacteria. While Protista represents the early evolution of eukaryotic cells.
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