Acoelomorpha and Xenoturbellida

Hejnol, Andreas

doi:10.1007/978-3-7091-1862-7_9

Cited by 8 publications

(7 citation statements)

References 50 publications

(71 reference statements)

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“…A different degree of morphological complexity of the NS is observable in the sister group of the Xenoturbellida: the Acoelomorpha (Acoela plus Nemertodermatida) [11]. There we can see, in some of its constituent taxa, obvious neural aggregations, positioned in the most anterior part of the body.…”

Section: Comparative Analysis Of Xenacoelomorpha Nervous System Morphologymentioning

confidence: 94%

“…Together with nemertodermatids, they constitute a taxon called Acoelomorpha, which is characterized by shared morphological features such as the epidermal ciliation, intestinal organization, certain glandular and sensory structures, and the limited presence of an extracellular matrix [1][2][3][4][5][6][7]. Recent phylogenetic analysis maintains that together with xenoturbellids [8], which form another taxon of considerably larger marine worms, they constitute the phylogenetic group Xenacoelomorpha [9][10][11]. This relationship is also supported by morphological similarities [1,3,7,[12][13][14][15][16][17][18], for instance the ultrastructure of the ciliary tips and the system of epidermal ciliary rootlets [5,6,15,18].…”

Section: The Phylogenetic Placement Of Xenacoelomorphamentioning

confidence: 99%

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Xenacoelomorpha: a case of independent nervous system centralization?

Gavilán

Perea-Atienza

Martı́nez

2016

Phil. Trans. R. Soc. B

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One contribution of 16 to a discussion meeting issue 'Homology and convergence in nervous system evolution'. Centralized nervous systems (NSs) and complex brains are among the most important innovations in the history of life on our planet. In this context, two related questions have been formulated: How did complex NSs arise in evolution, and how many times did this occur? As a step towards finding an answer, we describe the NS of several representatives of the Xenacoelomorpha, a clade whose members show different degrees of NS complexity. This enigmatic clade is composed of three major taxa: acoels, nemertodermatids and xenoturbellids. Interestingly, while the xenoturbellids seem to have a rather 'simple' NS (a nerve net), members of the most derived group of acoel worms clearly have ganglionic brains. This interesting diversity of NS architectures (with different degrees of compaction) provides a unique system with which to address outstanding questions regarding the evolution of brains and centralized NSs. The recent sequencing of xenacoelomorph genomes gives us a privileged vantage point from which to analyse neural evolution, especially through the study of key gene families involved in neurogenesis and NS function, such as G protein-coupled receptors, helixloop-helix transcription factors and Wnts. We finish our manuscript proposing an adaptive scenario for the origin of centralized NSs (brains).

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Section: Comparative Analysis Of Xenacoelomorpha Nervous System Morphologymentioning

confidence: 94%

Section: The Phylogenetic Placement Of Xenacoelomorphamentioning

confidence: 99%

Xenacoelomorpha: a case of independent nervous system centralization?

Gavilán

Perea-Atienza

Martı́nez

2016

Phil. Trans. R. Soc. B

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“…Whether these morphological commonalities are ancestral or derived in either extant acoels or extant planaria remains unknown. Both acoels and planaria exhibit atypical embryonic development [46,47]; whether these characteristics are ancestral or derived also remains unknown.…”

Section: Planaria Exemplify Basal Bilaterian Morphology and Wbr Capabilitymentioning

confidence: 99%

Does regeneration recapitulate phylogeny? Planaria as a model of body-axis specification in ancestral eumetazoa

Fields

Levin

2020

Communicative & Integrative Biology

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Metazoan body plans combine well-defined primary, secondary, and in many bilaterians, tertiary body axes with structural asymmetries at multiple scales. Despite decades of study, how axisdefining symmetries and system-defining asymmetries co-emerge during both evolution and development remain open questions. Regeneration studies in asexual planaria have demonstrated an array of viable forms with symmetrized and, in some cases, duplicated body axes. We suggest that such forms may point toward an ancestral eumetazoan form with characteristics of both cnidarians and placazoa.

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“…Xenacoelomorphs lack several nephrozoan features, including coeloms, excretory organs, a circulatory system, and a through gut, but share their bilateral symmetry with clearly defined body-axes and the mesodermal germ layer as synapomorphic characters with nephrozoans ( Jondelius et al. 2011 ; Hejnol 2015a , 2015b ; Haszprunar 2016 ; Hejnol and Pang 2016 ). Furthermore, xenacoelomorphs display highly diverse neuroanatomies and seem to have evolved clade-specific CNS with multiple nerve cords and brain-like structures, which have evolved convergently to those of other bilaterians ( Achatz and Martinez 2012 ; Hejnol 2015a ; Perea-Atienza et al.…”

Section: Introductionmentioning

confidence: 99%

Xenacoelomorph Neuropeptidomes Reveal a Major Expansion of Neuropeptide Systems during Early Bilaterian Evolution

Thiel

Franz‐Wachtel

Aguilera

et al. 2018

Molecular Biology and Evolution

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Neuropeptides are neurosecretory signaling molecules in protostomes and deuterostomes (together Nephrozoa). Little, however, is known about the neuropeptide complement of the sister group of Nephrozoa, the Xenacoelomorpha, which together form the Bilateria. Because members of the xenacoelomorph clades Xenoturbella, Nemertodermatida, and Acoela differ extensively in their central nervous system anatomy, the reconstruction of the xenacoelomorph and bilaterian neuropeptide complements may provide insights into the relationship between nervous system evolution and peptidergic signaling. Here, we analyzed transcriptomes of seven acoels, four nemertodermatids, and two Xenoturbella species using motif searches, similarity searches, mass spectrometry and phylogenetic analyses to characterize neuropeptide precursors and neuropeptide receptors. Our comparison of these repertoires with previously reported nephrozoan and cnidarian sequences shows that the majority of annotated neuropeptide GPCRs in cnidarians are not orthologs of specific bilaterian neuropeptide receptors, which suggests that most of the bilaterian neuropeptide systems evolved after the cnidarian–bilaterian evolutionary split. This expansion of more than 20 peptidergic systems in the stem leading to the Bilateria predates the evolution of complex nephrozoan organs and nervous system architectures. From this ancient set of neuropeptides, acoels show frequent losses that correlate with their divergent central nervous system anatomy. We furthermore detected the emergence of novel neuropeptides in xenacoelomorphs and their expansion along the nemertodermatid and acoel lineages, the two clades that evolved nervous system condensations. Together, our study provides fundamental insights into the early evolution of the bilaterian peptidergic systems, which will guide future functional and comparative studies of bilaterian nervous systems.

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Acoelomorpha and Xenoturbellida

Cited by 8 publications

References 50 publications

Xenacoelomorpha: a case of independent nervous system centralization?

Xenacoelomorpha: a case of independent nervous system centralization?

Does regeneration recapitulate phylogeny? Planaria as a model of body-axis specification in ancestral eumetazoa

Xenacoelomorph Neuropeptidomes Reveal a Major Expansion of Neuropeptide Systems during Early Bilaterian Evolution

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