Protists are eukaryotic creatures <you-carry-ah-tick>, meaning their DNA is enclosed in a nucleus inside the cell (unlike bacteria, which are prokaryotic <pro-carry-ah-tick> and have no nucleus to enclose their DNA. They’re not plants, animals or fungi, but they act enough like them that scientists believe protists paved the way for the evolution of early plants, animals, and fungi. Protists fall into four general subgroups: unicellular algae, protozoa, slime molds, and water molds.
Water molds are always found in wet environments, especially in fresh water sources and near the upper layers of moist soil.
Officially named Oomycota, they are also known as downy mildews and white rusts.
Water molds were long considered fungi because they produce fungi-like filamentous hyphae and feed on decaying tissue like rotting logs and mulch.
Scientists called to the scene, however, put any fears of menacing goo or alien creatures to rest by identifying the mass as an unusually large (46 centimeters or more than 14 inches in diameter) plasmodial slime mold.
Protozoa have been found in almost every kind of soil environment from peat bogs to arid desert sands. They teem in the deep sea as well as near the surface of waters, and can be found even in frigid Arctic and Antarctic waters.
Some species glow in the dark in a process called bioluminescence. These species contain a compound called luciferin (the same compound found in fireflies). The glow increases markedly if the algae cells are agitated, as when a ship churns through the water.
The most clearly plant-like algae, this species gets its namesake hue from high levels of chlorophyll.
Their cell walls are made up of cellulose, the same material that makes up the cell walls in larger, multicellular plants. Like plants, they store the food they make through photosynthesis as starches. Growing in large masses, these algae can form visible layers of slick, green scum on the surfaces and sides of ponds, puddles or damp soil.
Fossil records suggest that the first green algae originated 500 to 600 million years ago. Early algae probably gave rise to multicellular plants.
Algae also play an important role as the foundation for the aquatic food chain. All higher aquatic life forms depend either directly or indirectly on microscopic gardens of algae.
Most unicellular algae live in water, some dwell in moist soil, and others join with fungi to form lichens.