Polyps have little mesoglea but use the water in their guts as a hydrostatic skeleton. Physalia consists of a collection of polyps and medusae specialized for feeding, defense, and reproduction. The life cycle of a cnidarian may have a polyp and medusa stage, or it may have just the polyp. The medusa is usually the sexual form with either epidermal or gastrodermal gonads. The zygote develops into a swimming larva called a planula.
Polyps reproduce by asexual budding.
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.