A genetic model organism: Caenorhabditis elegans (Caeno, recent; rhabditis, rod; elegans, elegant) are hermaphroditic, free-living nematodes. The adult hermaphrodite is ~1 mm in length. Each hermaphrodite produces oocytes and sperm and can internally self-fertilize. Few males are also produced at low rate by unbalanced meiosis.

Easy cultivation: In the laboratory, C. elegans is cultivated in agar dishes seeded with Escherichia coli bacteria, which serve as a food source for the animals. It can be easily housed and cultivated in large numbers (>10,000 worms/petri dish) or can be frozen in liquid nitrogen and recovered many years later. C. elegans combine the practical advantage of hermaphrodite reproduction (large number of genetically identical animals and ease of maintaining strains by self fertilisation) with the experimental advantages of classical sexual reproduction (to transfer mutations, outcross, map traits, …).

Short life-cycle: Each hermaphrodite has several hundred self-progeny that reach reproductive maturity in 3–5 days, depending on cultivation temperature. Its lifespan last 2 to 3 weeks under suitable living conditions. This short life cycle greatly facilitates biological study of development and ageing.

A compact genome: The genome size of C. elegans is surprisingly compact: approximately 1/30 of that of human for roughly the same number of genes. ~80% of its genes have human homologues. Compactness, facilitate Next Generation Sequencing and cis-regulatory studies.

Many mutants and transgenic strains: Starting with an initial mutagenesis screen for mutations affecting worm shape & locomotion in the 70’s, labs and consortium around the world have now generated millions of mutants and transgenic strains available to the community for analysis.

Great for microscopy: C. elegans is transparent to light, turning it into a perfect organism to observe development or cell biology in-vivo, using contrast or fluorescent microscopy. Each individual contain a constant 959 somatic cells, including 302 neurons. The number and position of these cells during development and in the adult is constant.

diagram of connectivity of a neuron subset

A model for neuroscience: Unique to C. elegans is its compact nervous system consisting of just 302 neurons with reproducible location, functions and synaptic connectivity. The complex network made of ~8000 synapses and ~600 gap junctions is entirely described at the EM resolution. Neuronal differentiation and circuit assembly is well understood.