Archiannelida is also called Haprodrili. Two different zoologists gave it different names at roughly the same time and both names stuck. It is a form of marine worm in the phylum Annelid. Different members of this group use different methods of locomotion. Some use muscle contraction of the muscles lining the body cavity to move. Others use cilia lining the outside of the body to move. Another uses setae, or bristles, to help with locomotion. These setae prevent the organism from sliding backwards. These setae are mostly made of chitin, a carbohydrate polymer chain.