These organisms are free-living, typically very small and microscopic, although some species can reach up to one centimeter in size. Their bodies are cylindrical and covered with a hard coat, with both the anterior and posterior ends being as narrow as a needle. This body coat is composed of thick elastin proteins. Beneath the body coat, there are four layers of glands. The mouth opening is located at the front of the body and is surrounded by lips. Additionally, two unicellular glands called phasmid glands may or may not be present at the periphery of the organism. The tail is notched and divided into three parts, and cilia are present.