CHARACTERISTICS: diverse group of species, ranging from single-celled organisms to multi-cellular organisms like the seaweed, kelp; grouped together mainly because they cannot be classified as plants, animals, fungi or bacteria KNOWN SPECIES: 70,000 to 80,000; possibly 600,000 SIZE RANGE: microscopic to about 98 feet (less than 1 micron to about 30 meters) WHERE THEY LIVE: in soils, fresh waters and oceans, and as parasites inside other organisms