Their name is derived from the eight rows of cilia that resemble the teeth of a hair comb. The cilia beat in waves for propulsion. In addition, two long tentacles extend from the body for gathering prey. Although closely related to cnidarians, ctenophorans lack nematocysts and have slightly more advanced tissues. This phylum includes the free-living turbellarians and the parasitic flukes and tapeworms.
Pharynx tube extends to feed on whole small animals or to suck tissues from dead or wounded prey.
Protonephridia, with flame cells, regulate body fluid volume and composition. They are internal or external parasites of living vertebrate hosts. The body consists of an anterior scolex solely for attachment to the host's gut and a string of proglottids, each of which possesses both male and female organs. They are likely related to turbellarians because of the external cilia and tissue organization. Unlike flatworms, ribbon worms have a complete gut, a circulatory system, and separate sexes.