Caenorhabditis is a genus of nematodes which live in bacteria-rich environments like compost piles, decaying dead animals and rotting fruit. The name comes from Greek: caeno- (καινός (caenos) = new, recent); rhabditis = rod-like (ῥάβδος (rhabdos) = rod, wand). In 1900, Maupas initially named the species Rhabditis elegans, Osche placed it in the subgenus Caenorhabditis in 1952, and in 1955, Dougherty raised Caenorhabditis to the status of genus.[3]
The genus Caenorhabditis contains the noted model organism Caenorhabditis elegans and several other species for which a genome sequence is either available or currently being determined. The two most-studied species in this genus (C. elegans and C. briggsae) are both androdioecious (they have male and hermaphrodite sexes) whereas most other species are gonochoristic (they have male and female sexes).[4]
Caenorhabditis occupy various nutrient and bacteria rich environments. They do not form self-sustaining populations in soil, as it lacks enough organic matter. Juvenile worms and also dauer larvae can be transported by invertebrates including millipedes, insects, isopods, and gastropods. Some species also appear to be associated with vertebrates including zebu cattle, although the nature of this association is not clear. The species can be classified as 'phoretic' or 'necromenic' based on their relationships to their invertebrate hosts. A phoretic worm rides on the host until it finds a favorable environment, and then leaves. A necromenic worm waits for the host to die, and lives on the bacteria which thrive in the dead animal. Many species are capable of both phoretic and necromenic lifestyles.[6]
There are about 50 known species in this genus, some of them not yet formally described and named,[7] in spite of 15 of the species being named in one article 2014.[8] Based on ITS2 sequence comparison, these can be grouped like this:[8]
The Caenorhabditis species group with the 'Protorhabditis' group, containing species in the genera Protorhabditis, Diploscapter and Prodontorhabditis, on the one hand, and with Oscheius species, on the other hand, to form the 'Eurhabditis' group of Rhabditidae genera.[26]
Members of Caenorhabditis exclusively share 39 conserved signature indels that are found in the conserved regions of various proteins, such as the Rab44 protein and a poly ADP-ribose glycohydrolase protein (PARG-1), and are specifically located on surface-exposed loops.[27] These molecular markers help distinguish this genus from all other species, and their presence on surface-exposed loops suggest implications in protein-protein or protein-ligand interactions.[27]