Nematodes are roundworms that belong to the phylum NEMATODA. They are characterized by their unsegmented and bilaterally symmetrical bodies. Unlike other worms e.g flatworms, which have a two-way digestive system (food enters and waste comes out via same opening), nematodes have a unique digestive system or alimentary canal.
As rightly stated in this question, nematodes have a one-way or complete digestive tract/system. This means that they take in food through the MOUTH located at one end of their bodies and pass out waste through the ANUS located at the other end.
