Nematoda
Nematodes are round worms. Nematodes live anywhere and everywhere. Males are smaller than females, weird right?! Nematodes reproduce sexually. Roundworms have a complete digestive system. They also have a tough-waxy covering called the cuticle. Most roundworms are free-living but some need a host organism, most likely a human or an animal. Most humans have nematodes in them, as shown below in the video. There are about 50 species of parasitic roundworms. There is hookworm, ascaris, heartworm, and trincha. - er