Marine life from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. Microorganisms constitute more than 90% of the marine biomass. A microorganism (or microbe) is a microscopic living organism, which may be single-celled or multicellular. Microorganisms are very diverse and include all bacteria, archaea and most protozoa. This group also contains some species of fungi, algae, and certain microscopic animals, such as rotifers. Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists also classify viruses (and viroids) as microorganisms, but others consider these as nonliving. In
Evolutionary history of life identical cells. The red algae called "Bangiomorpha", dated at 1.2 Ga, is the earliest known organism that certainly has differentiated, specialized cells, and is also the oldest known sexually reproducing organism. The 1.43 billion-year-old fossils interpreted as fungi appear to have been multicellular with differentiated cells. The "string of beads" organism "Horodyskia", found in rocks dated from 1.5 Ga to 900 Ma, may have been an early metazoan; however, it has also been interpreted as a colonial foraminiferan. Animals are multicellular eukaryotes, and are distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only