Ascaris

Ascaris is a genus of parasitic nematode worms known as the "giant intestinal roundworms". One species, "A. suum", typically infects pigs, while another, "A. lumbricoides", affects humans, typically in sub-tropical and tropical areas with poor sanitation. "A. lumbricoides" is the largest intestinal roundworm and is the most common worm infection of humans, an infection known as "ascariasis". Infestation can cause morbidity, and sometimes death, by compromising nutritional status, affecting cognitive processes, inducing tissue reactions, such as granuloma, and provoking intestinal obstruction or rectal prolapse.
The roundworms are members of the phylum Nematoda. They are an extremely successful group; it is estimated that they represent 90% of all life on the seafloor.