The sponges (phylum Porifera)  are free-living, sessile, mostly marine, filter feeders.  They are considered to be primitive animals because they do not have cells organized into tissue layers. The Cnidarians do have tissue layers, most notably, nervous tissue.  They are radially symmetrical, and mostly carnivorous. Most are marine.   The Ctenophorans are similar to the Cnidarians in many ways but do not have cnidocytes, the cells that give Cnidarians their phylum name.  Ctenophorans have comb plates.