Roundworm

Caenorhabditis elegans is a free-living, transparent nematode about one millimetre long that lives in temperate soil environments and serves as the type species of its genus, an unsegmented pseudocoelomate with no respiratory or circulatory system. Most individuals are hermaphrodites, though rare males occur with tails specialised for mating. Sydney Brenner championed research into the organism beginning in 1963, and it became the first multicellular organism to have its whole genome sequenced and, in 2019, the first to have its complete neural wiring diagram, or connectome, mapped; research using it has contributed to four Nobel Prizes as of 2024.