What is Bilateria?
{{Automatic Taxobox | name = Bilateria | image = Animal_diversity_October_2007.jpg | image_width = 300px | image_caption = Diversity of bilaterians. | fossil_range = [[Ediacaran]] &ndash; Recent | taxon = Bilateria | phylum_authority = Hatschek, 1888}} The '''Bilateria''' are [[animal]]s which are bilaterally [[symmetry|symmetrical]]. They have front and a back end, an upside and downside, and a left and right side. Most animals are bilateral. == Main subgroups == * [[Deuterostome|Deuterostomia]] ** [[Echinodermata]] (20,000 species, 7000 living) ** [[Chordata]]. mostly [[Vertebrata]] (63,000 species) ** [[Hemichordata]] * [[Protostome|Protostomia]] ** [[Ecdysozoa]] (6 to 20 million species) <ref>Erwin T.L. 1982. Tropical forests: their richness in [[Coleoptera]] and other arthropod species. ''Coleopterists Bulletin''. '''36''', 74/5. See also [[Coevolution#Numbers of species]]</ref> ***[[Nematoda]] (20,000 species known +many more) ***[[Arthropoda]] (one to 10 million species) ** [[Lophotrochozoa]] ***[[Annelida]] (17,000 species) ***[[Platyhelminthes]] (20,000+ species) ***[[Mollusca]] (85,000+ species) ***[[Brachiopoda]] (5,000 fossil species) ***[[Rhombozoa]] ** [[Platyzoa]] ** Minor phyla (like [[Chaetognatha]]) Numbers are approximate; extinct species numbers cannot be known for most [[phyla]]. == Related pages == *[[List of animal phyla]] == References == {{Reflist}} [[category:Groups of phyla]]