Eucoelomata in which:-
The body is not clearly differentiated into regions, although there is some evidence of metamerism.
There is no definite head.
The gut is straight and the anus is terminal.
The nervous system consists of pre-oral ganglia joined by circum-oesophageal commissures to a double ventral nerve cord which has four ganglia along its length.
Sense organs consist of eye spots, bristles and spines.
The cuticle is non-chitinous.
There are four pairs of short unjointed legs, each with terminal claws.
Muscles of the body wall are single and smooth; they occur in bands.
The body cavity is a fluid-filled pseudocoelom.
Excretory organs are Malpighian tubules.
There is no blood vascular system.
The products of the gonads are shed through the terminal part of the intestine.
The sexes are separate.
The immature stage resembles the adult.