Protist Kingdom

At least a billion years before there were plants, animals or fungi, there were protists, the earliest descendents of the prokaryotes. Modern protists descended from near the base of the eukaryotic tree, and they vary in morphology and lifestyle more than any other group of organisms. They vary so extensively in cellular anatomy, ecological roles and life histories that few general characteristics can be cited without exceptions.
Protists can be found almost anywhere in the water.They are important constituents of plankton, the communities of organisms, mostly microscopic, that swim passively and weakly in the surface of oceans, ponds, and lakes. There are also bottom dwellers that attatch themselves to rocks. or creep through sand and silt. A particularly rich environment is that still water surface of lakes and ponds. Here, photosynthetic protists provide food for some other protists. Many can also be found in damp soil, leaf litter, and other moist habitats. In addition to free-living protists are the many symbionts that inhabit the body fluids, tissues or cells of hosts. These relationships can be parasitic or mutual. Some parasitic protists are important pathogens to animals, including the ones that can cause disease to humans.
Nearly all are aerobic in metabolism. As a group, they are the most diverse. Some use photosynthesis, ingestion or absorption for nutrition. Most had a cilia at one point of their life. All protists can reproduce asexually, but some can also reproduce sexually or at least use the process of meiosis and syngamy (the union of two gametes) to shuffle genes between two individuals that then go on to reproduce asexually.