These are free-living, very small and microscopic in size. However, the size of some species of animals is up to one centimeter. The body is cylindrical and covered with a hard coat. The anterior and posterior ends of the body are as narrow as a needle. The body-coat is made up of thick elastin proteins. Underneath the body-coat are four layers of glands. The mouth opening in the front of the body of animals is surrounded and characterized by lip. Two unicellular glands, phasmid glands, may or may not be present at the periphery of the organism. THe pharynx is progressively enlarged. Amphid looklike a cup.