And what are nematodes? They’re slender round worms; likely the most numerous multicellular animals on earth. Estimates are that a handful of soil will contain thousands of the microscopic worms, many of them parasites of insects, plants or animals. Nematodes have even been found at great depth (0.9–3.6 kilometers) below the surface of the earth in gold mines in South Africa. Free-living species are abundant, including nematodes that feed on bacteria, fungi, and other nematodes, yet the vast majority of species encountered are poorly understood biologically. There are nearly 20,000 described species classified in the phylum Nemata, although the total number of nematode species has been estimated to be about 1 million. Nematodes have been described as a tube within a tube; referring to the alimentary canal which extends from the mouth on the anterior end to the anus located near the tail. Nematodes possess digestive, nervous, excretory, and reproductive systems, but lack a discrete circulatory or respiratory system. In size they range from 0.3 mm to over 8 meters in length. Some can cause diseases affecting human beings, including ascariasis, trichuriasis, and hookworm disease. And now we know they have a brain. I wonder what they "think?" Scary thought!