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Temporal range: Ediacaran – Recent
Bilateria are all animals having a bilaterally symmetrical animals, they have front and a back end, as well as an upside and downside.
- Chaetognatha (affiliation uncertain) 
- Erwin T.L. 1982. Tropical forests: their richness in Coleoptera and other arthropod species. Coleopterists Bulletin. 36, 74/5. See also Co-evolution#Numbers of species
- Helfenbein, Kevin G. et al. 2004. The mitochondrial genome of Paraspadella gotoi is highly reduced and reveals that chaetognaths are a sister group to protostomes. Proceedings of the National Academy of Sciences of the United States of America 101(29), July 20 2004: 10639-10643
- Papillon, Daniel et al. 2004. Identification of chaetognaths as protostomes is supported by the analysis of their mitochondrial genome. Molecular Biology and Evolution 21(11), November 2004: 2122-2129