The coelom (or celom) is the main body cavity in many animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, it remains undifferentiated. In the past, and for practical purposes, coelom characteristics have been used to classify bilaterian animal phyla into informal groups.
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Caenorhabditis elegans (/ˌsiːnoʊræbˈdaɪtəs ˈɛləɡæns/) is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek caeno- (recent), rhabditis (rod-like) and Latin elegans (elegant). In 1900, Maupas initially named it Rhabditides elegans. Osche placed it in the subgenus Caenorhabditis in 1952, and in 1955, Dougherty raised Caenorhabditis to the status of genus.
C. elegans is an unsegmented pseudocoelomate and lacks respiratory or circulatory systems. Most of these nematodes are hermaphrodites and a few are males. Males have specialised tails for mating that include spicules.
The Aschelminthes (Aeschelminthes or Nemathelminthes), closely associated with the Platyhelminthes, are an obsolete phylum of pseudocoelomate and other similar animals that are no longer considered closely related and have been promoted to phyla in their own right. The term Aschelminth is now generally only used as an informal name for any member of the approximately ten different invertebrate phyla formerly included within Aschelminthes.
It is a polyphyletic group.