Taxonomy
Over the last decade, the work of developmental biologists and molecular phylogeneticists spawned new ideas about bilaterian relationships resulting in a paradigm shift.
The current widely accepted hypothesis, based on molecular data (mostly 18S rRNA sequences), divides bilateria into the following four superphylums : Deuterostomia, Ecdysozoa, Lophotrochozoa, and Platyzoa (sometimes included in Lophotrochozoa). The last three groups are also collectively known as Protostomia.
However, many skeptics emphasize the pitfalls and inconsistencies associated with the new data. Claus Nielsen, a professor of evolutionary invertebrate embryology at the Zoological Museum University of Copenhagen champions one of the most prominent alternative views based on morphological evidence. In his 2001 book Animal Evolution: Interrelationships of the Living Phyla, he maintains the traditional divisions of Protostomia and Deuterostomia.
Read more about this topic: Eumetazoa