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This tree represents the view of bilaterian relationships as it is currently emerging from analyses based on molecular data (mostly 18S rRNA sequences). For an alternative hypothesis of bilaterian relationships based on morphological data, see the Discussion of Phylogenetic Relationships.

Containing group: Animals

Discussion of Phylogenetic Relationships

Due to new evidence from developmental biology and molecular phylogenetics, ideas about bilaterian relationships have undergone a major paradigm shift within the last decade. The new hypotheses shown in the tree above are now widely accepted, but there are also many sceptics who emphasize the pitfalls and inconsistencies associated with the new data. One of the most prominent alternative views based on morphological evidence is championed by Nielsen (2001):

Other Names for Bilateria

• Triploblastica

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Information on the Internet

• Assembling the Tree of Life: An Integrated Approach to the Origin and Diversification of Protostomes.