The enigmatic phylum Placozoa
is the only animal phylum harboring a single species, Trichoplax adhaerens
(live photograph of an adult specimen), only. New genetic methods, however, have revealed that this phylum indeed harbor more than 100 to 200 yet undescribed species. This case of under-represented diversity in a phylum is unique. These animals are of particular importance to systematics and evolution since they might represent the ancestors of all other metazoans.