Roundworm: Caenorhabditis elegans

Although anatomically and genetically simple, C. elegans mimics the life cycle of humans. Starting from a fertilized egg, it undergoes a complex development that gives rise to excretory, reproductive, digestive, and neuromuscular organ systems. The cell lineages of each of the 959 adult somatic cells have been directly observed, as has the fact that an additional unique set of 131 cells die during development. These deaths would have gone unnoticed, except for their demise was observable under the microscope. These observations led to the concept that apoptosis is a vital feature of development in multicellular organisms, and that it enables the shaping and carving of organs and tissues.

Today C. elegans remains one of the foremost model systems used in genetic research. Advanced descriptions have been made of its anatomy, cell lineages, developmental genetics, neural development, and reproductive cycle. The recent discovery of a mutation that doubles its life expectancy suggests that this "worm" will continue to expand its usefulness as a model system for the study of aging. Its growing significance as a member of the large, evolutionarily successful Nematoda phylum highlights the importance of C. elegans to the study of the genes involved in adaptive evolution.

SEE ALSO APOPTOSIS; CLONING GENES; GENOME; MAPPING; MODEL ORGANISMS.