The dawn of bilaterian animals: the case of acoelomorph flatworms
Abstract
The origin of the bilaterian metazoans from radial ancestors is one of the biggest puzzles in animal evolution. A way to solve it is to identify the nature and main features of the last common ancestor of the bilaterians (LCB). Recent progress in molecular phylogeny has shown that many platyhelminth flatworms, regarded for a long time as basal bilaterians, now belong to the lophotrochozoan protostomates. In contrast, the LCB is now considered a complex organism bearing several features of modern bilaterians. Here we discuss an alternative view, in which acoelomorph (Acoela + Nemertodermatida) flatworms, which do not belong to the Platyhelminthes, represent the earliest extant bilaterian clade. Sequences from ribosomal and other nuclear genes, Hox cluster genes, and reinterpretation of some morphological features strongly support the basal position of acoelomorphs arguing against a complex LCB. This reconstruction backs the old planuloid–acoeloid hypothesis and may help our understanding of the evolution of body axes, Hox genes and the Cambrian explosion. BioEssays 26:1046–1057, 2004. © 2004 Wiley Periodicals, Inc.
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Acoel flatworms are recognized as the sister group to the remaining bilaterians.
“the fact that acoel flatworms are now recognized as the sister group to the remaining bilaterians (Bagun ˜a ` & Riutort 2004; Peterson et al. 2005; Sempere et al. 2007)”
From The Ediacaran emergence of bilaterians: congruence between the genetic and the geological fossil records (2008) · cites this paper as Bagunà & Riutort 2004
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- Authors
- Baguñà, J., & Riutort, M.
- Affiliations
- Universitat de Barcelona (ES)
- Corresponding author
- Baguñà, Jaume
- ORCID
- Riutort, Marta
- Venue
- BioEssays
- Publisher
- Wiley
- Published
- 2004-09-20
- Volume
- 26
- Issue
- 10
- Pages
- 1046-1057
- ISSN
- 0265-9247 (ISSN-L)
- 1521-1878
- OpenAlex
- W2043656979
- Cited by
- 164
- References
- 12
- Citations by year
- 2026: 1 · 2025: 1 · 2024: 1 · 2023: 2 · 2022: 1 · 2021: 3 · 2020: 1 · 2019: 4 · 2018: 3 · 2017: 2 · 2016: 5 · 2015: 7 · 2014: 4 · 2013: 5 · 2012: 4
- FWCI
- 2.31
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- BioEssays (publishedVersion)
- PubMed (publishedVersion)
- Funders
- Generalitat de Catalunya and the Ministerio de Ciencia y Tecnologia
- Topics
- Physical Sciences › Earth and Planetary Sciences › Paleontology › Marine Invertebrate Physiology and Ecology
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Developmental Biology and Gene Regulation
- Life Sciences › Agricultural and Biological Sciences › Ecology, Evolution, Behavior and Systematics › Invertebrate Taxonomy and Ecology
- Keywords
- bilaterian origin, Acoela, Nemertodermatida, Hox genes, Cambrian explosion, molecular phylogeny, ribosomal genes
- MeSH terms
- Animals, Biological Evolution, Genes, Homeobox, Multigene Family, Models, Biological, Phylogeny, Platyhelminths
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