The New View of Animal Phylogeny

Halanych, Kenneth M.

doi:10.1146/annurev.ecolsys.35.112202.130124

Cited by 428 publications

(291 citation statements)

References 177 publications

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“…A major result was to shift all acoelomate and pseudocoelomate groups, traditionally considered at the base of the Bilateria, into the Ecdysozoa and Lophotrochozoa (Adoutte et al 2000). Further nuclear and mitochondrial markers and combined morphological-molecular studies also support these findings (Peterson & Eernisse 2001;Halanych 2004).…”

Section: Molecular Phylogeny Of the Bilateria: New Datamentioning

confidence: 89%

Back in time: a new systematic proposal for the Bilateria

Baguñà

Martinez

Paps

et al. 2008

Phil. Trans. R. Soc. B

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Conventional wisdom suggests that bilateral organisms arose from ancestors that were radially, rather than bilaterally, symmetrical and, therefore, had a single body axis and no mesoderm. The two main hypotheses on how this transformation took place consider either a simple organism akin to the planula larva of extant cnidarians or the acoel Platyhelminthes (planuloid-acoeloid theory), or a rather complex organism bearing several or most features of advanced coelomate bilaterians (archicoelomate theory). We report phylogenetic analyses of bilaterian metazoans using quantitative (ribosomal, nuclear and expressed sequence tag sequences) and qualitative (HOX cluster genes and microRNA sets) markers. The phylogenetic trees obtained corroborate the position of acoel and nemertodermatid flatworms as the earliest branching extant members of the Bilateria. Moreover, some acoelomate and pseudocoelomate clades appear as early branching lophotrochozoans and deuterostomes. These results strengthen the view that stem bilaterians were small, acoelomate/pseudocoelomate, benthic organisms derived from planuloid-like organisms. Because morphological and recent gene expression data suggest that cnidarians are actually bilateral, the origin of the last common bilaterian ancestor has to be put back in time earlier than the cnidarian-bilaterian split in the form of a planuloid animal. A new systematic scheme for the Bilateria that includes the Cnidaria is suggested and its main implications discussed.

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Section: Molecular Phylogeny Of the Bilateria: New Datamentioning

confidence: 89%

Back in time: a new systematic proposal for the Bilateria

Baguñà

Martinez

Paps

et al. 2008

Phil. Trans. R. Soc. B

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“…Current molecular phylogenies based on several markers place the Bryozoa along with the annelids, mollusks, brachiopods, and phoronids within the Lophotrochozoa (Halanych, 2004;Passamaneck and Halanych, 2006). Although their position relative to other phyla within the Lophotrochozoa has not been well resolved, it is plausible that the bryozoans occupy a more basal position within this supraphyletic clade (Waeschenbach et al, 2006).…”

Section: Larval Morphology and Phylogenymentioning

confidence: 99%

The morphology and evolutionary significance of the ciliary fields and musculature among marine bryozoan larvae

Santagata

2007

Journal of Morphology

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Despite the embryological and anatomical disparities present among lophotrochozoan phyla, there are morphological similarities in the cellular arrangements of ciliated cells used for propulsion among the nonfeeding larval forms of kamptozoans, nemerteans, annelids, mollusks, and bryozoans. Evaluating whether these similarities are the result of convergent selective pressures or a shared (deep) evolutionary history is hindered by the paucity of detailed cellular information from multiple systematic groups from lesser-known, and perhaps, basal evolutionary phyla such as the Bryozoa. Here, I compare the ciliary fields and musculature among the major morphological grades of marine bryozoan larvae using light microscopy, SEM, and confocal imaging techniques. Sampling effort focused on six species from systematic groups with few published accounts, but an additional four well-known species were also reevaluated. Review of the main larval types among species of bryozoans and these new data show that, within select systematic groups of marine bryozoans, there is some conservation of the cellular arrangement of ciliary fields and larval musculature. However, there is much more morphological diversity in these structures than previously documented, especially among nonfeeding ctenostome larval types. This structural and functional diversification reflects species differences in the orientation of the apical disc during swimming and crawling behaviors, modification of the presumptive juvenile tissues, elongation of larval forms in the aboral-oral axis, maximizing the surface area of cell types with propulsive cilia, and the simplification of ciliary fields and musculature within particular lineages due to evolutionary loss. Considering the embryological origins and functional plasticity of ciliated cells within bryozoan larvae, it is probable that the morphological similarities shared between the coronal cells of bryozoan larvae and the prototrochal cells of trochozoans are the result of convergent functional solutions to swimming in the plankton. However, this does not rule out cell specification pathways shared by more closely related spiralian phyla. Overall, among the morphological grades of larval bryozoans, the structural variation and arrangement of the main cell groups responsible for ciliary propulsion have been evolutionarily decoupled from the more divergent modifications of larval musculature. The structure of larval ciliary fields reflects the functional demands of swimming and substrate exploration behaviors before metamorphosis, but this is in contrast to the morphology of larval musculature and presumptive juvenile tissues that are linked to macroevolutionary differences in morphogenetic movements during metamorphosis.

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“…This period culminated with the proposition of a new view of animal phylogeny at odds with the traditional paradigm of a steady increase toward morphological complexity, and revealing instead the major role played by secondary simplification from complex ancestors (Adoutte et al, 2000;Lwoff, 1944). Despite these undeniable achievements, the resolving power provided by 18S rRNA and other single genes is nevertheless limited, and a number of open questions in animal phylogeny remained to be answered (Halanych, 2004).…”

Section: Introductionmentioning

confidence: 99%

Additional molecular support for the new chordate phylogeny

Delsuc

Tsagkogeorga

Lartillot

et al. 2008

Genesis

216

178

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Summary: Recent phylogenomic analyses have suggested tunicates instead of cephalochordates as the closest living relatives of vertebrates. In direct contradiction with the long accepted view of Euchordates, this new phylogenetic hypothesis for chordate evolution has been the object of some skepticism. We assembled an expanded phylogenomic dataset focused on deuterostomes. Maximum-likelihood using standard models and Bayesian phylogenetic analyses using the CAT site-heterogeneous mixture model of amino-acid replacement both provided unequivocal support for the sister-group relationship between tunicates and vertebrates (Olfactores). Chordates were recovered as monophyletic with cephalochordates as the most basal lineage. These results were robust to both gene sampling and missing data. New analyses of ribosomal rRNA also recovered Olfactores when compositional bias was alleviated. Despite the inclusion of 25 taxa representing all major lineages, the monophyly of deuterostomes remained poorly supported. The implications of these phylogenetic results for interpreting chordate evolution are discussed in light of recent advances from evolutionary developmental biology and genomics. genesis 46:592-604, 2008. V V C 2008 Wiley-Liss, Inc.

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The New View of Animal Phylogeny

Cited by 428 publications

References 177 publications

Back in time: a new systematic proposal for the Bilateria

Back in time: a new systematic proposal for the Bilateria

The morphology and evolutionary significance of the ciliary fields and musculature among marine bryozoan larvae

Additional molecular support for the new chordate phylogeny

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