Clonorchis sinensis (a trematode/fluke), Anisakis (a nematode/roundworm) and Diphyllobothrium (a cestode/tapeworm). It is a nematode (roundworm) and a common intestinal parasite or helminth, especially in humans. Loa loa is the filarial nematode (roundworm) species that causes "Loa loa" filariasis. Strongyloides stercoralis is a human pathogenic parasitic roundworm causing the disease strongyloidiasis. "Toxocara canis" (dog roundworm) eggs in dog feces can cause toxocariasis. "T. trichiura" is the third most common nematode (roundworm) infecting humans. Its main use is for protecting livestock against roundworm, strongyles and pinworms. Virchow worked out the life cycle of a roundworm "Trichinella spiralis". Ascaridia galli is a parasitic roundworm belonging to the phylum Nematoda. Six Hox genes are dispersed in the genome of "Caenorhabditis elegans", a roundworm. He established that human roundworm infection occurs via contaminated pork. Small-animal models include the fruit fly, the roundworm "C. elegans", and the zebrafish. Lower invertebrates, such as roundworm "C. elegans", also have only one arrestin. Nematodes, cestodes, paramphistomes; and the roundworm "Setaria labiatopapillosa" have also been isolated from the hartebeest. Fibrates have been shown to extend lifespan in the roundworm "C. elegans".