C. elegans is a small soil-dwelling nematode. You can get a better idea of it’s anatomy by looking at these interactive 3D models as well as the marvelous WormAtlas. It possesses many advantages as a model animal, including simple growth conditions, rapid generation time with an invariant cell lineage, and well-developed genetic and molecular tools. Importantly, it was the first multicellular animal to have its complete genome sequenced. The C. elegans research community is well served by a comprehensive database, Wormbase (access the local mirror), that seemlessly integrates genetic and molecular data, and a catholic web-server maintained by Leon Avery. It is clear that many of the discoveries made with C. elegans are relevant to the study of higher organisms. This extends beyond fundamental cellular processes, such as transcription, translation, DNA replication and cellular metabolism. For this reason, and because of its intrinsic practical advantages, C. elegans has proved to be an invaluable tool for the understanding of vertebrate neuronal growth and pathfinding, apoptosis and intra- and inter-cellular signaling pathways, to give but a few examples. It is proving to be a powerful model for studying host-pathogen interactions.
The most complete resource for C. elegans is now WormBook.
It replaces "C. elegans II".