The Caenorhabditis elegans, a roundworm belonging to the phylum Nematoda, is commonly used as a biological model system for research. This information is sourced from the NCI Thesaurus, with the code C14303.The Caenorhabditis elegans, a roundworm belonging to the phylum Nematoda, is commonly used as a biological model system for research. This information is sourced from the NCI Thesaurus, with the code C14303.