The only surviving parazoans are the sponges , which belong to the phylum Porifera . Some include Placozoa , a phylum that consists of only one species , Trichoplax adhaerens , in the division , but they are also sometimes placed in the subkingdom Agnotozoa . The only surviving parazoans are the sponges , which belong to the phylum Porifera , and one surviving species ( Trichoplax adhaerens ) in the phylum Placozoa .