Priapulida, phylum consisting of 17 species of predatory, unsegmented marine worms that live in the sand and mud at the sea bottom. The largest are 4 to 6 in. (10–17 cm) long, but the majority of species are less than .05 in. (.13 cm) in size. The animals consist of a spiny body with an anterior that can be everted or inverted into the trunk for locomotion or feeding. Spines around the mouth and in the pharnyx are everted to capture prey. The sexes are separate and the egg is fertilized externally, hatching into a larval stage in all but one species. Fossil species can be traced to the Cambrian period, but zoologists do not agree on an interpretation of the lining of the body cavity. This would determine if priapulids are coelomates or pseudocoelomates.