Nematoda
Nematodes, or roundworms, are a very diverse animal phylum. They inhabit a very broad range of environments, and consist of approximately one million species. The trait that makes Nematodes distinct from cnidarians and flatworms is that nematodes have tubular digestive systems with openings at both ends. Most species of the nematode phylum are parasitic.
Excretory System
The excretory system of the nematode phylum is unique in the way salt is excreted from the body. In many marine nematodes, one or two unicellular ''renette glands" excrete salt through a pore on the underside of the animal, close to the pharynx. In most other nematodes, these specialised cells have been replaced by an organ consisting of two parallel ducts connected by a single transverse duct. This transverse duct opens into a common canal that runs to the excretory pore.
Examples
Trichinella spiralis is a species of the nematode phylum
Enterobius vermicularis - (The Human Pinworm)
Ascaris lumbricoides (Large Roundworm of Man)