@misc{crossref1963the,
    title = "The Evolution of the Metazoa",
    year = "1963",
    url = "https://doi.org/10.1016/c2013-0-08245-x",
    doi = "10.1016/c2013-0-08245-x",
    openalex = "W4256710260"
}

@misc{hadzi1963the,
    author = "Hadzi, J.",
    title = "The evolution of the metazoa",
    year = "1963",
    url = "https://doi.org/10.5962/bhl.title.6821",
    doi = "10.5962/bhl.title.6821",
    openalex = "W2109017224"
}

@article{whitear1964the,
    author = "Whitear, Mary and Hadzi, Jovan",
    title = "The Evolution of the Metazoa",
    year = "1964",
    journal = "The Journal of Animal Ecology",
    url = "https://doi.org/10.2307/2578",
    doi = "10.2307/2578",
    number = "3",
    openalex = "W4229859634",
    pages = "529",
    volume = "33"
}

@article{chapman1965metazoan,
    author = "CHAPMAN, G.",
    title = "Metazoan Evolution",
    year = "1965",
    journal = "Nature",
    url = "https://doi.org/10.1038/207339b0",
    doi = "10.1038/207339b0",
    number = "4995",
    openalex = "W4254937058",
    pages = "339-340",
    volume = "207"
}

@article{newth1965metazoan,
    author = "Newth, D. R.",
    title = "Metazoan Evolution",
    year = "1965",
    journal = "BMJ",
    url = "https://doi.org/10.1136/bmj.1.5435.641-c",
    doi = "10.1136/bmj.1.5435.641-c",
    number = "5435",
    openalex = "W4247941486",
    pages = "641-642",
    volume = "1"
}

@article{doi101111j155856461974tb00804x,
    author = "Hedgpeth, Joel W.",
    title = "EVOLUTION OF THE METAZOAN LIFE CYCLE",
    year = "1974",
    journal = "Evolution",
    abstract = "Journal Article EVOLUTION OF THE METAZOAN LIFE CYCLE Get access Joel W. Hedgpeth Joel W. Hedgpeth Pacific Marine Station Dillon Beach Calif Search for other works by this author on: Oxford Academic Google Scholar Evolution, Volume 28, Issue 4, 1 December 1974, Page 696, https://doi.org/10.1111/j.1558-5646.1974.tb00804.x Published: 01 December 1974 Article history Received: 01 June 1974 Published: 01 December 1974",
    url = "https://doi.org/10.1111/j.1558-5646.1974.tb00804.x",
    doi = "10.1111/j.1558-5646.1974.tb00804.x",
    openalex = "W2617181777"
}

@incollection{crossref1977chapter,
    title = "Chapter 2 General Patterns of Metazoan Evolution",
    year = "1977",
    booktitle = "Developments in Palaeontology and Stratigraphy",
    url = "https://doi.org/10.1016/s0920-5446(08)70322-4",
    doi = "10.1016/s0920-5446(08)70322-4",
    openalex = "W2144968695",
    pages = "27-57",
    references = "doi101086282398, doi101086406830, doi101093aesa383396, doi101111j150239311971tb01864x, doi101130spe89p63, doi1023072405671, openalexw1480175384, openalexw2145250129, openalexw2418669733, openalexw3126336940"
}

@book{crossref1977patterns,
    title = "Patterns of Evolution as Illustrated by the Fossil Record",
    year = "1977",
    booktitle = "Developments in Palaeontology and Stratigraphy",
    url = "https://doi.org/10.1016/s0920-5446(08)x7012-8",
    doi = "10.1016/s0920-5446(08)x7012-8",
    openalex = "W563635432"
}

@book{valentine1977general2,
    author = "Valentine, J. W",
    title = "General Patterns in Metazoan Evolution, in Hallam, A., ed., Patterns of Evolution",
    year = "1977",
    publisher = "New York, Elsevier Science Publishers",
    note = "talkorigins\_source = {true}; raw\_reference = {Valentine, J. W., 1977, General Patterns in Metazoan Evolution, in Hallam, A., ed., Patterns of Evolution: New York, Elsevier Science Publishers.}"
}

@article{cloud1982the,
    author = "Cloud, Preston and Glaessner, Martin F.",
    title = "The Ediacarian Period and System: Metazoa Inherit the Earth",
    year = "1982",
    journal = "Science",
    abstract = "The Ediacarian, here defined as the initial period and system of the Phanerozoic Eon, is characterized by the oldest known multicellular animal life. The distinctive biotal assemblage comprises naked Metazoa, represented in the type region by 26 species in 18 genera and 4 or more phyla, plus simple metazoan surface tracks. Elements of this unique biota appeared worldwide at low paleolatitudes, following terminal Proterozoic glaciation. Ediacarian history lasted from about 670 million to 550 million years ago. This interval, plus Early Cambrian, was the time during which metazoan life diversified into nearly all of the major phyla and most of the invertebrate classes and orders subsequently known.",
    url = "https://doi.org/10.1126/science.217.4562.783",
    doi = "10.1126/science.217.4562.783",
    number = "4562",
    openalex = "W1998183413",
    pages = "783-792",
    volume = "217",
    references = "cloud1976beginnings, cloud1979earliest, doi101017s0016756800155815, doi101038scientificamerican066172, doi101086628416, doi101111j150239311969tb01258x, doi101126science13334591105, doi101126science21044731013, doi101144pygs313211, doi102475ajs2728752, doi105281zenodo16238847, lo1980microbial"
}

@misc{cloud1982the1,
    author = "Cloud, P. and Glaessner, M. F",
    title = "The Ediacarian Period and System",
    year = "1982",
    howpublished = "Metazoa inherit the Earth: Science, v. 217, p. 783-792",
    note = "talkorigins\_source = {true}; raw\_reference = {Cloud, P., and Glaessner, M. F., 1982, The Ediacarian Period and System: Metazoa inherit the Earth: Science, v. 217, p. 783-792.}"
}

@book{doi1010079781489924278,
    author = "Lipps, Jere H. and Signor, Philip W.",
    title = "Origin and Early Evolution of the Metazoa",
    year = "1992",
    booktitle = "Topics in geobiology",
    url = "https://doi.org/10.1007/978-1-4899-2427-8",
    doi = "10.1007/978-1-4899-2427-8",
    openalex = "W659320407"
}

@article{doi10100797830348726521,
    author = "Adoutte, A. and Philippe, H.",
    title = "The major lines of metazoan evolution: summary of traditional evidence and lessons from ribosomal RNA sequence analysis.",
    year = "1993",
    journal = "EXS",
    booktitle = "Comparative Molecular Neurobiology",
    url = "https://www.semanticscholar.org/paper/80d79f7e12f335df2214e22eccf6c2a258f1f196",
    doi = "10.1007/978-3-0348-7265-2\_1",
    is_oa = "true",
    pages = "1-30",
    semanticscholar_citation_count = "65",
    semanticscholar_id = "80d79f7e12f335df2214e22eccf6c2a258f1f196"
}

@article{doi101038361219a0,
    author = "Morris, Simon Conway",
    title = "The fossil record and the early evolution of the Metazoa",
    year = "1993",
    journal = "Nature",
    url = "https://doi.org/10.1038/361219a0",
    doi = "10.1038/361219a0",
    openalex = "W2143380472",
    references = "doi101016001670379290064p, doi1010160301926885900518, doi101016030192688590066x, doi101016s0959437x05801923, doi101017cbo9780511601064002, doi101038345802a0, doi101093oso97801985771880010001, doi101111j146364091991tb00303x, doi101111j150239311989tb01332x, doi101126science1585174, doi101126science1598573, doi101126science2464928339, doi101126science3277277, doi101144gsjgs14920171, doi101144gsjgs14940607, doi1023072992562, doi105860choice273873"
}

@article{doi101017s0022336000027700,
    author = "Lieberman, B.",
    title = "Testing the Darwinian legacy of the Cambrian radiation using trilobite phylogeny and biogeography",
    year = "1999",
    journal = "Journal of Paleontology",
    abstract = "Since the publication of Darwin (1859), the biological meaning of the Cambrian radiation has been debated. Most commentators agree, however, that the Cambrian radiation is fundamentally a time of major metazoan cladogenesis. In and of itself this does not necessarily mean that unique evolutionary processes operated during the Cambrian radiation. Phylogenetic analysis has been used to study the tempo of speciation during the radiation, and thus far there is no need to invoke special rules relating to the tempo of evolution. Instead, what seems unique about the Cambrian radiation is its place as an important episode in the history of life—that is, as the first major radiation of the Metazoa. Although the tempo of evolution during the Cambrian radiation may not have been uniquely high, there were largely unique tectonic events that transpired during the late Neoproterozoic and Early Cambrian, such as extensive cratonic fragmentation. Biogeographic analysis of Early Cambrian olenelloid trilobites reveals that these tectonic events powerfully influenced evolutionary and distributional patterns in this diverse and abundant trilobite group. This emphasizes the importance of physical earth history in generating evolutionary patterns. In the general study of macroevolutionary patterns and processes, earth history phenomena emerge as powerful forces influencing the history of life and provide insights into evolution that can best be inferred by paleontological data.",
    url = "https://www.semanticscholar.org/paper/8ceb1444407c52f3fcf4391995c4e95012cd7bdd",
    doi = "10.1017/S0022336000027700",
    is_oa = "true",
    number = "2",
    pages = "176-181",
    semanticscholar_citation_count = "32",
    semanticscholar_id = "8ceb1444407c52f3fcf4391995c4e95012cd7bdd",
    volume = "73"
}

@article{doi101126science28354091919,
    author = "Ruiz‐Trillo, Iñaki and Riutort, Marta and Littlewood, D. Timothy J. and Herniou, Elisabeth A. and Baguñà, Jaume",
    title = "Acoel Flatworms: Earliest Extant Bilaterian Metazoans, Not Members of Platyhelminthes",
    year = "1999",
    journal = "Science",
    abstract = "Because of their simple organization the Acoela have been considered to be either primitive bilaterians or descendants of coelomates through secondary loss of derived features. Sequence data of 18S ribosomal DNA genes from non-fast evolving species of acoels and other metazoans reveal that this group does not belong to the Platyhelminthes but represents the extant members of the earliest divergent Bilateria, an interpretation that is supported by recent studies on the embryonic cleavage pattern and nervous system of acoels. This study has implications for understanding the evolution of major body plans, and for perceptions of the Cambrian evolutionary explosion.",
    url = "https://doi.org/10.1126/science.283.5409.1919",
    doi = "10.1126/science.283.5409.1919",
    openalex = "W2019581837",
    references = "doi101007bf00186547, doi101007bf02101694, doi101038290470a0, doi101038387489a0, doi101073pnas972111359, doi101093nar2781767, doi101093oxfordjournalsmolbeva025664, doi101093oxfordjournalsmolbeva026241, doi101093sysbio274401, doi101111j109600311998tb00338x, doi101146annurevbi46070177003041, doi1023072412923, hadzi1963the, openalexw1505736461"
}

@article{doi101126science2885467841,
    author = "Martin, Mark W. and Grazhdankin, Dmitriy and Bowring, Samuel A. and Evans, David A.D. and Fedonkin, M. A. and Kirschvink, Joseph L.",
    title = "Age of Neoproterozoic Bilatarian Body and Trace Fossils, White Sea, Russia: Implications for Metazoan Evolution",
    year = "2000",
    journal = "Science",
    abstract = "A uranium-lead zircon age for a volcanic ash interstratified with fossil-bearing, shallow marine siliciclastic rocks in the Zimnie Gory section of the White Sea region indicates that a diverse assemblage of body and trace fossils occurred before 555.3 +/- 0.3 million years ago. This age is a minimum for the oldest well-documented triploblastic bilaterian Kimberella. It also makes co-occurring trace fossils the oldest that are reliably dated. This determination of age implies that there is no simple relation between Ediacaran diversity and the carbon isotopic composition of Neoproterozoic seawater.",
    url = "https://doi.org/10.1126/science.288.5467.841",
    doi = "10.1126/science.288.5467.841",
    openalex = "W1993655526",
    references = "doi101139e87124, doi1023073515363"
}

@incollection{syvanen2002temporal,
    author = "Syvanen, Michael",
    title = "Temporal Patterns of Plant and Metazoan Evolution Suggest Extensive Polyphyly",
    year = "2002",
    booktitle = "Horizontal Gene Transfer",
    url = "https://doi.org/10.1016/b978-012680126-2/50038-4",
    doi = "10.1016/b978-012680126-2/50038-4",
    openalex = "W1221894428",
    pages = "383-395",
    references = "doi101007bf02983073, doi101016b9781483232119500097, doi10103846528, doi101073pnas86166201, doi101073pnas902411558, doi101126science17940781144, doi101126science2715248470, doi101126science2715249640, doi101126science2745287568, doi101126science2865441947"
}

@article{doi101146annurevecolsys34012103144032,
    author = "Willig, Michael R. and Kaufman, Dawn M. and Stevens, Richard D.",
    title = "Latitudinal Gradients of Biodiversity: Pattern, Process, Scale, and Synthesis",
    year = "2003",
    journal = "Annual Review of Ecology Evolution and Systematics",
    abstract = "▪ Abstract The latitudinal gradient of decreasing richness from tropical to extratropical areas is ecology's longest recognized pattern. Nonetheless, notable exceptions to the general pattern exist, and it is well recognized that patterns may be dependent on characteristics of spatial scale and taxonomic hierarchy. We conducted an extensive survey of the literature and provide a synthetic assessment of the degree to which variation in patterns (positive linear, negative linear, modal, or nonsignificant) is a consequence of characteristics of scale (extent or focus) or taxon. In addition, we considered latitudinal gradients with respect to generic and familial richness, as well as species evenness and diversity. We provide a classification of the over 30 hypotheses advanced to account for the latitudinal gradient, and we discuss seven hypotheses with most promise for advancing ecological, biogeographic, and evolutionary understanding. We conclude with a forward-looking synthesis and list of fertile areas for future research.",
    url = "https://doi.org/10.1146/annurev.ecolsys.34.012103.144032",
    doi = "10.1146/annurev.ecolsys.34.012103.144032",
    openalex = "W2099879847",
    references = "doi10100797814615695341, doi1010160040580970900390, doi101017cbo9780511623387, doi10103835012228, doi101038365636a0, doi101046j13652699200100563x, doi101086282070, doi101086282398, doi101086285144, doi101086321317, doi101111j155856461960tb03057x, doi101111j155856461963tb03295x, doi101126science25951001439, doi101126science2925517673, doi101146annurevecolsys33030602152151, doi1018900012965820020831771tuntob20co2, doi1023071218190, doi1023071939924, doi1023071941447, doi1023071943563, doi1023072407089, doi105860choice332720, openalexw1532540194"
}

@article{isaeva2006topological,
    author = "Isaeva, Valeria and Presnov, Eugene and Chernyshev, Alexey",
    title = "Topological Patterns in Metazoan Evolution and Development",
    year = "2006",
    journal = "Bulletin of Mathematical Biology",
    url = "https://doi.org/10.1007/s11538-006-9063-2",
    doi = "10.1007/s11538-006-9063-2",
    number = "8",
    openalex = "W2054193849",
    pages = "2053-2067",
    volume = "68",
    references = "doi101007b98869, doi1010179781108120241010, doi101093aesa323657, doi101119113295, doi101126science28454201677, doi1015159780691212920, doi1015159781400881802, doi1023072981858, openalexw1576847343"
}

@article{doi101111j14754983200600614x,
    author = "Erwin, Douglas H.",
    title = "DISPARITY: MORPHOLOGICAL PATTERN AND DEVELOPMENTAL CONTEXT",
    year = "2007",
    journal = "Palaeontology",
    abstract = "Abstract: The distribution of organic forms is clumpy at any scale from populations to the highest taxonomic categories, and whether considered within clades or within ecosystems. The fossil record provides little support for expectations that the morphological gaps between species or groups of species have increased through time as it might if the gaps were created by extinction of a more homogeneous distribution of morphologies. As the quantitative assessments of morphology have replaced counts of higher taxa as a metric of morphological disparity, numerous studies have demonstrated the rapid construction of morphospace early in evolutionary radiations, and have emphasized the difference between taxonomic measures of morphological diversity and quantitative assessments of disparity. Other studies have evaluated changing patterns of disparity across mass extinctions, ecomorphological patterns and the patterns of convergence within ecological communities, while the development of theoretical morphology has greatly aided efforts to understand why some forms do not occur. A parallel, and until recently, largely separate research effort in evolutionary developmental biology has established that the developmental toolkit underlying the remarkable breadth of metazoan form is largely identical among Bilateria, and many components are shared among all metazoa. Underlying this concern with disparity is a question about temporal variation in the production of morphological innovations, a debate over the relative significance of the generation of new morphologies vs. differential probabilities of their successful introduction, and the relative importance of constraint, convergence and contingency in the evolution of form.",
    url = "https://doi.org/10.1111/j.1475-4983.2006.00614.x",
    doi = "10.1111/j.1475-4983.2006.00614.x",
    openalex = "W2091948436",
    references = "doi101016jprecamres200511003, doi101017cbo9781139164856, doi101017s009483730001263x, doi101017s0094837300015864, doi101073pnas050586297, doi101111j1525142x200600101x, doi101666009483731999251mditer20co2, doi1016660094837320000260056cefisg20co2, doi1016660094837320040300652atrode20co2, doi105860choice333929, foote1996perspective, openalexw2055967869, openalexw635257420"
}

@article{doi101146annurevearth35031306140258,
    author = "Hughes, Nigel C.",
    title = "The Evolution of Trilobite Body Patterning",
    year = "2007",
    journal = "Annual Review of Earth and Planetary Sciences",
    abstract = "The good fossil record of trilobite exoskeletal anatomy and ontogeny, coupled with information on their nonbiomineralized tissues, permits analysis of how the trilobite body was organized and developed, and the various evolutionary modifications of such patterning within the group. In several respects trilobite development and form appears comparable with that which may have characterized the ancestor of most or all euarthropods, giving studies of trilobite body organization special relevance in the light of recent advances in the understanding of arthropod evolution and development. The Cambrian diversification of trilobites displayed modifications in the patterning of the trunk region comparable with those seen among the closest relatives of Trilobita. In contrast, the Ordovician diversification of trilobites, although contributing greatly to the overall diversity within the clade, did so within a narrower range of trunk conditions. Trilobite evolution is consistent with an increased premium on effective enrollment and protective strategies, and with an evolutionary trade-off between the flexibility to vary the number of trunk segments and the ability to regionalize portions of the trunk.",
    url = "https://doi.org/10.1146/annurev.earth.35.031306.140258",
    doi = "10.1146/annurev.earth.35.031306.140258",
    openalex = "W2126678118",
    references = "doi101016jasd200501005, doi101093icb431185, doi101111j1469185x1986tb00464x, doi101111j155856461971tb01868x, doi101666060171, doi101826182000751171987, doi10182618200093301197301"
}

@article{doi101002bies200800214,
    author = "Mikhailov, Kirill V. and Константинова, А. В. and Никитин, М. А. and Troshin, Peter V and Rusin, L.Y. and Lyubetsky, Vassily and Panchin, Yuri V. and Mylnikov, Alexander P. and Moroz, Leonid L. and Kumar, Sudhir and Aleoshin, Vladimir V.",
    title = "The origin of Metazoa: a transition from temporal to spatial cell differentiation",
    year = "2009",
    journal = "BioEssays",
    abstract = "For over a century, Haeckel's Gastraea theory remained a dominant theory to explain the origin of multicellular animals. According to this theory, the animal ancestor was a blastula-like colony of uniform cells that gradually evolved cell differentiation. Today, however, genes that typically control metazoan development, cell differentiation, cell-to-cell adhesion, and cell-to-matrix adhesion are found in various unicellular relatives of the Metazoa, which suggests the origin of the genetic programs of cell differentiation and adhesion in the root of the Opisthokonta. Multicellular stages occurring in the complex life cycles of opisthokont protists (mesomycetozoeans and choanoflagellates) never resemble a blastula. Here, we discuss a more realistic scenario of transition to multicellularity through integration of pre-existing transient cell types into the body of an early metazoon, which possessed a complex life cycle with a differentiated sedentary filter-feeding trophic stage and a non-feeding blastula-like larva, the synzoospore. Choanoflagellates are considered as forms with secondarily simplified life cycles.",
    url = "https://doi.org/10.1002/bies.200800214",
    doi = "10.1002/bies.200800214",
    openalex = "W2099958663",
    references = "doi101002sici10974687200001243135aidjmor330co2, hadzi1963the"
}

@article{doi101007s0043500800753,
    author = "Suschenko, Dominick and Purschke, G.",
    title = "Ultrastructure of pigmented adult eyes in errant polychaetes (Annelida): implications for annelid evolution",
    year = "2009",
    journal = "Zoomorphology",
    url = "https://www.semanticscholar.org/paper/0c03bcedbefa8e7925b91b0df6f3a23c4411dee1",
    doi = "10.1007/s00435-008-0075-3",
    is_oa = "true",
    number = "1",
    pages = "75-96",
    semanticscholar_citation_count = "24",
    semanticscholar_id = "0c03bcedbefa8e7925b91b0df6f3a23c4411dee1",
    volume = "128"
}

@article{doi101111j143904691978tb00919x,
    author = "v. Salvini‐Plawen, L.",
    title = "On the origin and evolution of the lower Metazoa",
    year = "2009",
    journal = "Journal of Zoological Systematics \& Evolutionary Research",
    abstract = "Summary Recent advancements in infrastructure and new theories propagating different ideas on the early metazoan evolution initiated a comparison and in some aspects revision of existing concepts. 1 Based upon discussed monophyly of Eukaryota, premetazoan organization must have been mitotic, heterotroph, and naked eukaryotes which had stabilized the presence of diplo-somes. 2 The Chonoflagellata constitute the only serious candidates for metazoan precursors in being provided with a diplosome and monociliate collar cells; sexual reproduction is no prerequisite, but rather newly acquired. 3 Parazoa (Porifera) and Histozoa (Eumetazoa) constitute a distinctly monophyletic entity. This cognition is especially supported by the overlapping presence of and direct developmental continuity between choanocytes and microvilli-collar cells in Porifera, the latter being likewise primitive in Histozoa. 4 The monophyly of all Metazoa-as demonstrated-sets all die-or polyphyletic concepts aside; the latter are discussed. 5 The origin of Metazoa is accepted as having taken place via blastula-like organisms with a subsequent diploblastic organization through cell immigration. Diploblasty through invagination is considered to constitute a process of ontogenetical compensation, and the Gastraea-Theory is rejected as far as it is strictly correlated with the functionally untenable and morphologically inconsistent Enterocoel-Theory. 6 The monophyletic entity of Parazoa and Histozoa is only possible within early (larval) levels of organization which, therefore, are the only features the comparison of which is permitted. This cognition demonstrates that the choanosome in adult Porifera corresponds to the ectoderm (but not to the entoderm) in Histozoa. 7 The basic organization of the Histozoa (Eumetazoa) is accepted to have been made up of sexual, heteropolar planuloids provided with biradial to bilateral symmetry. 8 Biradial-symmetrical, pelagic Protoplanulae are assumed to have given rise to the Collaria (Ctenophora). 9 Bilateral-symmetrical, bottom-tied Archiplanulae are accepted for the origin of Cnidaria as well as of Bilateria (Planula-Theory). 10 The evolution of Bilateria from planula-like ancestors is most strikingly supported by the organization of Diopisthoporus (Turbellaria-Acoela). The shift of the initially posterior mouth towards ventral can be recapitulatively observed in various groups of Spiralia which are accepted as constituting the more conservative Bilateria. 11 Bottom-pelagic, lateral-symmetrical Archiplanulae gave rise to the Cnidaria, primarily characterized by some initial nematocysts as well as by one (!) pair of rudimentary lateral tentacles. The definitive deviation of such organisms by settling resulted in lateral-symmetrical, two-tentacles polypid forms as the original Cnidaria. 12 Both main lines of Cnidaria, Anthozoa and Tesserazoa (= Scyphozoa, Cubozoa, and Hydrozoa), variously recapitulate their bilateral ancestry (arrangements of septa or tentacles, etc. respectively). 13 Within the - primitively biradial-Tesserazoa, the Scyphozoa constitute the most conservative class (periderm tube, septal muscles and hydrostatic canal system). Their medusae merely constitute distal portions (including gonads) of the polyps. 14 The Cubomedusae meanwhile have been proved to develop through a typical metamorphosis out of radial-symmetrical polyps. Accordingly, they are accepted as a class proper, the Cubozoa, because they no longer fit within the scyphozoan frame (despite the synapo-morphic characters of rhopalia and gastric filaments). 15 After having developed first dimorphism and subsequently pelagic reproductive individuals (= medusae, which still demonstrate several ancestral characters: tetramery canal system), most hydropolyps secondarily adapted towards a cycloradial symmetry. Resume Sur I'origine et revolution des Métazoaires inférieurs De récentes observations au plan de l'ultrastructure et de nouvelles théories soutenant des conceptions différentes sur l'évolution précoce des métazoaires nous amènent à comparer les idées formulées jusqu'ici et à modifier quelques theories. 1 En vue de la monophylie admise pour les eucaryotes, l'organisation prémétazoaire a dûČetre celle d'un eucaryote nu, mitotique et héterotrophe chez lequel la présence de diplosomes etait déjà stable. 2 Ce sont les seuls Choanoflagellés qui présentent les conditions de précurseurs des métazoaires, car lis sont pourvus de diplosomes et de cellules à collerette de microvillosités. La reproduction sexuelle n'était pas une condition préalable, mais elle a été acquise indepen-damment. 3 Les parazoaires (Porifera) et les histozoaires (Eumetazoa) représentent une unité décidé-ment monophylétique. Ceci est particuliérement appuyé par la présence simultanée et par la continuité ontogénétique des choanocytes et des cellules à collerette de microvillosités chez les porifères-ce dernier type de cellules étant egalement primitif chez les histozoaries. 4 La monophylie des métazoaires exclut tout concept di-ou polyphylétique; ces concepts sont discutés. 5 L'origine des métazoaires est supposé au niveau d'organismes blastloides, suivis d'une organisation diploblastique par immigration cellulaire. La diploblastie par invagination est considéré comme événement de compensation ontogénetique, et la Théorie de la Gastraea est refusée en tant qu'elle est strictement corrélée avec la Théorie de 1'EnterocoeI qui est fonctionellement insoutenable et morphologiquement contradictoire. 6 L'unité monophylétique des Parazoa et Histozoa est seulement compréhensible aux stades precoces (larvaires) des organisations, done seuls ces charactéres sont comparables. Il en résulte que le choanosome des poriféres adultes correspond à L'ectoderme (et non pas à l'entoderme) des histozoaires. 7 L'organisation basale des Histozoa (Eumetazoa) a dûêtre celle de planuloides héteropo-laires, sexuels avec une symétrie biradiale à bilaterale. 8 Des Protoplanulae pélagiques et biradio-symétriques sont supposés d'avoir donné naissance aux Collaria (Ctenophora). 9 Des Archiplanulae quasi benthiques et bilatéro-symétriques ont dûêtre à l'origine des Cnidaria aussi bien que des Bilateria (Théorie de la Planula). 10 L'évolution des Bilateria á partir des ancêtres planuloides est appuyée de façon convaicante par l'organisation de Diopisthoporus (Turbellaria-Acoela). Le déplacement de la bouche d'abord postérieure à une position ventrale est observé comme récapitulation dans divers groupes des Spiralia, lesquels semblent représenter les Bilateria plus conservateurs. 11 Les Archiplanulae bentho-pélagique et latéro-symétriques ont donné naissance aux Cnidaria, characterisés à l'origine par quelques nématocystes primitifs et par une seule (!) paire de tentacules latérales rudimentaries. La déviation définitive de tels organismes par la fixation a conduit aux polypes latéro-symétriques avec deux tentacules, représetant les cnidaires primitifs. 12 Les deux branches principals des Cnidaria, e'est à dire les Anthozoa et les Tesserazoa (= Scyphozoa, Cubozoa, et Hydrozoa), souvent récapitulent leur ancienne structure bilatérale (disposition des septa ou tentacles, etc.). 13 Parmi les Tesserazoa (à l'origine biradiales), les Scyphozoa représentent la classe la plus conservatrice (tube de périderme, muscles septales et système hydrostatique des canaux). Leur méduses ne représentent que les parties distales (y compris les gonades) des polypes. 14 On a pu démontrer que les Cubomedusae se développent à travers une métamorphose typique des polypes qui ont une symétrie cycloradiale. Par conséquence, ils sont acceptés comme une classe separée, les Cubozoa, car ils ne s'accordent plus au concept des Scyphozoa (malgré les charactères synapomorphiques des rhopalia et des filaments gastnques). 15 Après avoir developpé d'abord un dimorphisme et puis une différation en individus reproducteurs pélagiques (= méduses, qui démontrent encore quelques charactères ancestraux: symétrie biradiale, système des canaux), la plupart des hydropolypes se sont adaptés à une symétrie cycloradiale. Zusammenfassung Uber Ursprung und Entwicklung der niedren Metazoa Im Hinblick auf jüngste Erkenntnisse im ultrastrukturellen Bereich und auf neuere Vorstel-lungen zur Frühentwicklung der Metazoen wird eine Gegenüberstellung und Teilrevision bestehender Theorien gegeben. Auf der Basis der diskutierten, monophyletischen Entstehung der Eukaryota sind für den Ursprung der Metazoen nur nackte, heterotrophe Organismen mit mitotischer Zellteilung verständlich, in welchen der Besitz zweier rechtwinkelig zueinander angeordneter Centriolen (Diplosom) stabilisiert war. Innerhalb der bekannten Protisten bilden die Choanoflagellata die einzige ernsthafte Ausgangsgruppe, da allein sie durch das Diplosom wie auch durch ihren Microvilli-Kragen charakteristische, praerequisite Merkmale der Metazoa aufweisen; die geschlechtliche Fortpflanzung mit vorherrschend diploider Phase ist neu erworben. Entgegen verschiedener Theorien kann festgestellt werden, daβ die Parazoa und Histozoa eine monophyletisdie Einheit darstellen, belegt durch 1. die übereinstimmende geschlechtliche Fortpflanzung, 2. den detaillierten Aufbau des Microtubular-Komplexes (Flagellen, Cilien, Centriolen), 3. die Struktur der Spermien, 4. die monociliaren Microvilli-Kragenzellen sowie 5. die von ökologischen und ethnologischen Bedingungen unabhängigen, primären Symmetne-verhältnisse. Besondere Bedeutung kommt hierbei dem simultanén und ontogenetisch ineinander übergehenden Vorhandensein von Choanocyten=Microvilli-Kragenzellen bei Porifera zu. In Anbetracht dieser belegbaren monophyletischen Einheit aller Metazoa sind Vorstellungen mit diphyletischem (polyphyletischem) Ursprung nicht mehr annehmbar; sie werden dis-kutiert. Der Ursprung der Metazoa läβt sich einsichtig auf Choanoflagellaten-Kolonien zurück-führen, welche sich zu pelagischen, achsiaten Hohlkugel-Organismen (Blastaeae) mit sexueller Fortpflanzung entwickelten. Die anschlieβende Differenzierung und Radiation solcher Blastaea-Organismen zur diploblastischen Organisation durch Immigration zu soliden, sexuellen Planuloiden (Planaeae) erscheint hierbei aufschluβreicher gegenüber einer Diploblastie durch Invagination; letzterer Modus (Gastraea-Theorie) ist allein durch die strikte Korrelation mit der jedoch funktionell unhaltbaren und morphologisch widerspriichlichen Enterocoel-Theorie von Bedeutung, und erscheint als ontogenetischer Kompensations-Vorgang. Die primar̈ unabhängigen Differenzierungen zur Diploblastie und zur Gastrulation einerseits, sowie anderer-seits die zu einem Vergleidi von Parazoa und Histozoa heranzuziehenden monophyletisch-gemeinsamen, ausschlieβlich frühen (larvalen) Entwicklungsstadien lassen feststellen, daβ das Choanosom der Porifera dem Ektoderm (und nicht dem Entoderm) der Histozoa entspricht. Als Basis-Organisation der Histozoa (Eumetazoa) sind sexuelle, heteropolare Planuloide (mit Sinnespol, Urdarmhöhle durch Delamination, fakultativer Mundöffnung) mit biradialen bis bilateralen Symmetrieverhältnissen wahrscheinlidi, welche als biradiale Protoplanulae mit pelagischer Lebensweise den Collaria (Ctenophora) den Ursprung gaben. Bilateral-symmetrische, Boden-bezogene Archiplanulae können in direkter Entwicklung als Basis der Bilateria angenommen werden (Planula-Theorie), was durch die Modell-Organisation von Diopistho-porus (Turbellaria-Acoela) deutlich gestützt wird; die sekundäre Verlagerung der terminalen Mundöffnung nach ventral wird hierbei innerhalb verschiedener Spiralia recapitulativ wieder-holt. Nach vorliegendem Wissensstand erscheinen daher die niedrigen Spiralia (Plathelminthes-Turbellaria) als Ursprungsgruppe der Bilateria (deren weitere Differenzierung kurz skizziert wird). Von gleicherweise bilateral-symmetrischen, Boden-pelagischen Archiplanulae lassen sich die Cnidaria ableiten, primär gekennzeichnet durch die Differenzierung von Cniden und von einem (!) Paar lateraler Tentakelanlagen. Die definitive Deviation durch Festsetzen der bilateralen Organismen mit Ubergang zur sessilen Lebensweise führte zur Basis-Organisation der rezenten Cnidaria, dem-im Gegensatz zu den bisherigen Theorien-zwei-tentakeligen Polyp. Die weitere-von den bestehenden Vorstellungen ebenfalls abweichende-Entwicklung der Cnidaria läβt eine Aufspaltung in die Anthozoa mit einem Paar Protosepten und anschlieβencer octomerer Bilateralsymmetrie (davon sekundär abgeleitet die hexamer-bilateralen Gruppen), und in die Tesserazoa (Scyphozoa, Cubozoa, Hydrozoa) erkennen. Letztere zeichnen sich durch die Abwandlung zur Tetramerie und durch Differenzierung einer Peridermrohre aus, deren Verschluβapparat die Differenzierung von vier Septalmuskeln und des hydrostatischen Kanalsystems bedingte. Die Entwicklung von Medusen, einmal durch periodisches Abschnüren der Tentakelscheibe (Strobila der Scyphozoa) und andererseits durch Dimorphismus mit pelagischen Geschlechtstieren (Hydrozoa) sind als jeweils unabhängige Differenzierungen hervor-zuheben. Die von den Scyphozoa abgespaltenen Cubomedusae (synapomorphe Merkmale: Rhopalia und Gastralfilamente) zeichnen sich u. a. durch eine echte Metamorphose aus und sind als ein eigener, gleichrangiger Entwicklungszweig (Cubozoa) festzustellen; die Cubopolypen sind, wie audi die Hydropolypen, mit ihrer angepaβten Radiärsymmetrie als secundär-abge-leitet zu betrachten.",
    url = "https://doi.org/10.1111/j.1439-0469.1978.tb00919.x",
    doi = "10.1111/j.1439-0469.1978.tb00919.x",
    openalex = "W2020771624",
    references = "doi101111j146363951970tb00436x, hadzi1963the"
}

@article{doi1011861471214810101,
    author = "Traylor-knowles, Nikki and Hansen, U. and DuBuc, Timothy Q. and Martindale, M. and Kaufman, L. and Finnerty, J.",
    title = "The evolutionary diversification of LSF and Grainyhead transcription factors preceded the radiation of basal animal lineages",
    year = "2010",
    journal = "BMC Evolutionary Biology",
    abstract = "BackgroundThe transcription factors of the LSF/Grainyhead (GRH) family are characterized by the possession of a distinctive DNA-binding domain that bears no clear relationship to other known DNA-binding domains, with the possible exception of the p53 core domain. In triploblastic animals, the LSF and GRH subfamilies have diverged extensively with respect to their biological roles, general expression patterns, and mechanism of DNA binding. For example, Grainyhead (GRH) homologs are expressed primarily in the epidermis, and they appear to play an ancient role in maintaining the epidermal barrier. By contrast, LSF homologs are more widely expressed, and they regulate general cellular functions such as cell cycle progression and survival in addition to cell-lineage specific gene expression.ResultsTo illuminate the early evolution of this family and reconstruct the functional divergence of LSF and GRH, we compared homologs from 18 phylogenetically diverse taxa, including four basal animals (Nematostella vectensis, Vallicula multiformis, Trichoplax adhaerens, and Amphimedon queenslandica), a choanoflagellate (Monosiga brevicollis) and several fungi. Phylogenetic and bioinformatic analyses of these sequences indicate that (1) the LSF/GRH gene family originated prior to the animal-fungal divergence, and (2) the functional diversification of the LSF and GRH subfamilies occurred prior to the divergence between sponges and eumetazoans. Aspects of the domain architecture of LSF/GRH proteins are well conserved between fungi, choanoflagellates, and metazoans, though within the Metazoa, the LSF and GRH families are clearly distinct. We failed to identify a convincing LSF/GRH homolog in the sequenced genomes of the algae Volvox carteri and Chlamydomonas reinhardtii or the amoebozoan Dictyostelium purpureum. Interestingly, the ancestral GRH locus has become split into two separate loci in the sea anemone Nematostella, with one locus encoding a DNA binding domain and the other locus encoding the dimerization domain.ConclusionsIn metazoans, LSF and GRH proteins play a number of roles that are essential to achieving and maintaining multicellularity. It is now clear that this protein family already existed in the unicellular ancestor of animals, choanoflagellates, and fungi. However, the diversification of distinct LSF and GRH subfamilies appears to be a metazoan invention. Given the conserved role of GRH in maintaining epithelial integrity in vertebrates, insects, and nematodes, it is noteworthy that the evolutionary origin of Grh appears roughly coincident with the evolutionary origin of the epithelium.",
    url = "https://bmcecolevol.biomedcentral.com/counter/pdf/10.1186/1471-2148-10-101",
    doi = "10.1186/1471-2148-10-101",
    is_oa = "true",
    number = "1",
    semanticscholar_citation_count = "42",
    semanticscholar_id = "dbfa861b086fd644648ec8a671a462bc6736e5a2",
    volume = "10"
}

@article{doi1031274etd1808102915,
    author = "Haen, Karri M.",
    title = "Mitochondrial genome evolution in the Metazoa: Insights from Class Hexactinellida (Phylum Porifera) and Phylum Cnidaria",
    year = "2010",
    url = "https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=2798\&context=etd",
    doi = "10.31274/ETD-180810-2915",
    is_oa = "true",
    semanticscholar_id = "323d240890f42e988790af209d1461300fb7bd6f"
}

@article{s21f1b7613872d5efca5e58a22849832a21d38ddfe,
    author = "Kranz, Alexandrea M",
    title = "Deciphering the genetic mechanisms that regulate sexual development in the abalone: Vasa, Nanos and Dmrt gene expression in the vetigastropod Haliotis asinina",
    year = "2010",
    journal = "Queensland's institutional digital repository (The University of Queensland)",
    abstract = "Throughout the Metazoa, reproductive success and species survival is dependent on sexual dimorphisms that ultimately result in the fusion of haploid gametes to form a diploid zygote. These sexual dimorphisms are formed by two different, but integral, developmental processes that are both are intimately related to an organisms’ reproductive strategy. These two developmental processes are germ-line development and somatic sexual development. Typically sexual development is studied in model organisms with a focus either on the ‘general sex determination hierarchy’ that diverts an initially ambiguous embryo down a specific path of sexual development or with a focus on early germ-line cell specification. Given that the presence of two morphologically distinct sexes is a common characteristic of animal species, a better understanding of metazoan sexual development requires an expansion of focus both beyond these described fields of research and in non-model organisms covering diverse phylogenetic lineages and life history strategies. To contribute to a better understanding of metazoan sexual development, I use a candidate gene approach to further our understanding of both germ-line and somatic sexual development in a non-model organism, the gastropod mollusc Haliotis asinina. First, as Haliotis asinina has an unknown germ-line origin, I isolate the germ-line markers Vasa and Nanos – conserved genes involved in germ cell specification and differentiation in all animals so far studied – from H. asinina and characterize their expression during embryonic and larval development. The spatial and temporal expression of both HasVasa and HasNanos indicate that the H. asinina germ-line arises from the 4d cell lineage and that primordial germ cells (PGCs) are not specified exclusively by maternally-inherited determinants. As such, I infer that inductive signals play an important role in specifying PGCs in H. asinina. As HasVasa appears to be expressed in a sub-population of HasPL10 expressing cells - a putative stem cell marker - during early larval development, I also hypothesis that HasVasa is expressed in a population of undifferentiated multipotent cells, from which the PGCs are segregated later during development. After the formation of the germ-line, PGCs typically must migrate and integrate into the somatic gonad primordium. Next, to examine early gonad development, I isolated and characterized Doublesex and mab-3 related transcription factor (Dmrt) genes in H. asinina, as they are the only known factors involved in (somatic) sexual development that are conserved across distant animal phyla. I isolated three Dmrt genes from H. asinina – namely HasDmrt1, HasDmrta1 and HasDmrta2 – and examined their spatial and temporal expression patterns during embryonic, larval and early juvenile development. One these genes - HasDmrt1 - is expressed throughout larval development, with transcripts localized to a field in the left dorsal region of the visceral mass that also express the germ cell markers HasVasa and HasNanos. This spatial expression pattern is compatible with HasDmrt1 playing a role in primordial gonad development. In contrast, the other two Dmrt genes - HasDmrta1 and HasDmrta2 – are expressed in diverse cell lineages and tissues that do not appear to overlap with HasDmrt1, suggesting that these genes function in a range of other non-sexual developmental processes during this time. All of the candidate genes described so far – HasVasa, HasNanos, HasDmrt1, HasDmrta1 and HasDmrta2 – potentially have a role in regulating sexual development in diverse animal phyla. To improve our understanding of the role these selected candidate genes might play in sexual development in the gastropod mollusc Haliotis asinina, I have analyzed their temporal expression patterns throughout the period of gonad development and maturation via real-time quantitative RT-PCR (RT-qPCR). In addition, as putative markers of gamete maturation and sex, I also investigate the expression of the male gamete recognition protein HasLysin and its female counterpart HasVerl. From my RT-qPCR data I draw three main conclusions. First my results are consistent with the HasDmrt1 DM domain being involved in both sex-specific development during the time of early gonad differentiation and in adult testis maturation. Second I find that the expression patterns of the germ-line genes HasVasa and HasNanos are consistent with the expression and functional data available for ecdysozoans and deuterostomes that shows that Vasa is involved in the process of germ cell differentiation and Nanos is involved in the process of adult germ-line stem cell maintenance. Third I find that HasLysin and HasVerl are not exclusively expressed in males or females respectively and that these genes are not adequate markers of sex in H. asinina juveniles. In summary, by studying the spatial and temporal expression patterns of – the germ-line genes HasVasa and HasNanos, the stem cell marker HasPL10, the Dmrt genes HasDmrt1, HasDmrta1 and HasDmrta2 and the gamete recognition proteins HasLysin and HasVerl – I have formed a more complete picture of H. asinina sexual development. This study also provides further evidences that genes such as Vasa, Nanos and Dmrts appear highly conserved throughout evolution, while their upstream effectors and downstream targets may indeed evolve independently.",
    url = "https://www.semanticscholar.org/paper/1f1b7613872d5efca5e58a22849832a21d38ddfe",
    is_oa = "true",
    openalex = "W157125508",
    semanticscholar_id = "1f1b7613872d5efca5e58a22849832a21d38ddfe"
}

@article{doi10118620419139322,
    author = "Sorrentino, Gina M and Gillis, William Q. and Oomen-Hajagos, Jamina and Thomsen, G.",
    title = "Conservation and evolutionary divergence in the activity of receptor-regulated smads",
    year = "2012",
    journal = "EvoDevo",
    abstract = "Activity of the Transforming growth factor-β (TGFβ) pathway is essential to the establishment of body axes and tissue differentiation in bilaterians. Orthologs for core pathway members have been found in all metazoans, but uncertain homology of the body axes and tissues patterned by these signals raises questions about the activities of these molecules across the metazoan tree. We focus on the principal canonical transduction proteins (R-Smads) of the TGFβ pathway, which instruct both axial patterning and tissue differentiation in the developing embryo. We compare the activity of R-Smads from a cnidarian (Nematostella vectensis), an arthropod (Drosophila melanogaster), and a vertebrate (Xenopus laevis) in Xenopus embryonic assays. Overexpressing NvSmad1/5 ventralized Xenopus embryos when expressed in dorsal blastomeres, similar to the effects of Xenopus Smad1. However, NvSmad1/5 was less potent than XSmad1 in its ability to activate downstream target genes in Xenopus animal cap assays. NvSmad2/3 strongly induced general mesendodermal marker genes, but weakly induced ones involved in specifying the Spemann organizer. NvSmad2/3 was unable to induce a secondary trunk axis in Xenopus embryos, whereas the orthologs from Xenopus (XSmad2 and XSmad3) and Drosophila (dSmad2) were capable of doing so. Replacement of the NvSmad2/3 MH2 domain with the Xenopus XSmad2 MH2 slightly increased its inductive capability, but did not confer an ability to generate a secondary body axis. Vertebrate and cnidarian Smad1/5 have similar axial patterning and induction activities, although NvSmad1/5 is less efficient than the vertebrate gene. We conclude that the activities of Smad1/5 orthologs have been largely conserved across Metazoa. NvSmad2/3 efficiently activates general mesendoderm markers, but is unable to induce vertebrate organizer-specific genes or to produce a secondary body axis in Xenopus. Orthologs dSmad2 and XSmad3 generate a secondary body axis, but activate only low expression of organizer-specific genes that are strongly induced by XSmad2. We suggest that in the vertebrate lineage, Smad2 has evolved a specialized role in the induction of the embryonic organizer. Given the high level of sequence identity between Smad orthologs, this work underscores the functional importance of the emergence and fixation of a few divergent amino acids among orthologs during evolution.",
    url = "https://evodevojournal.biomedcentral.com/counter/pdf/10.1186/2041-9139-3-22",
    doi = "10.1186/2041-9139-3-22",
    is_oa = "true",
    number = "1",
    semanticscholar_citation_count = "1",
    semanticscholar_id = "7ca5abc1646687cc850211e0ba17c2830142b2a4",
    volume = "3"
}

@article{doi10166613072,
    author = "Grazhdankin, Dmitriy",
    title = "Patterns of Evolution of the Ediacaran Soft-Bodied Biota",
    year = "2014",
    journal = "Journal of Paleontology",
    abstract = "When each of the Avalon-, Ediacara-, and Nama-type fossil assemblages are tracked through geological time, there appear to be changes in species composition and diversity, almost synchronized between different sedimentary environments, allowing a subdivision of the late Ediacaran into the Redkinian, Belomorian and Kotlinian geological time intervals. The Redkinian (580–559 Ma) is characterized by first appearance of both eumetazoan traces and macroscopic organisms (frondomorphs and vendobionts) in a form of Avalon-type communities in the inner shelf environment, whereas coeval Ediacara-type communities remained depauperate. The Belomorian (559–550 Ma) is marked by the advent of eumetazoan burrowing activity in the inner shelf, diversification of frondomorphs, migration of vendobionts from the inner shelf into higher energy environments, and appearance of tribrachiomorphs and bilateralomorphs. Ediacaran organisms formed distinctive ecological associations that coexisted in the low-energy inner shelf (Avalon-type communities), in the wave- and current-agitated shoreface (Ediacara-type communities), and in the high-energy distributary systems (Nama-type communities). The Kotlinian (550–540 Ma) witnessed an expansion of the burrowing activity into wave- and current-agitated shoreface, disappearance of vendobionts, tribrachiomorphs and bilateralomorphs in wave- and current-agitated shoreface, together with a drop in frondomorph diversity. High-energy distributary channel systems of prodeltas served as refugia for Nama-type communities that survived until the end of the Ediacaran and disappeared when the burrowing activity reached high-energy environments. This pattern is interpreted as an expression of ecosystem engineering by eumetazoans, with the Ediacaran organisms being progressively outcompeted by bilaterians.",
    url = "https://doi.org/10.1666/13-072",
    doi = "10.1666/13-072",
    openalex = "W2121360736",
    references = "doi101130g325801, doi101144pygs313211"
}

@article{doi104236am2014517255,
    author = "Isaeva, V. V. and Kasyanov, Nickolay V. and Presnov, E.",
    title = "Topology in Biology: Singularities and Surgery Transformations in Metazoan Development and Evolution",
    year = "2014",
    journal = "Applied Mathematics",
    abstract = "The review presents a topological description and interpretation (analysis) of some events in metazoan development and evolution through the use of well-known mathematical concepts and theorems (using topological approach). It is the topological language that can provide strict and adequate description of various phenomena in developmental and evolutionary transformations. Topological singularities inevitably arising and transforming during early development destroy the preexisting pattern of symmetry. The symmetry breaking of preexisting spatial pattern plays a critical role in biological morphogenesis in development and evolution. Some events of early development are interpreted in terms of symmetry breakdown and related to well-known mathematical theorems. A topological inevitability of some developmental events through the use of classical topological concepts is discussed. The topological approach makes it possible to consider the succession of spherical surgeries, which change the topological genus of an animal body surface. We model the biological shape as a set of smooth, closed, oriented surfaces—membrane or epithelial layers. Membrane and epithelial surfaces are boundary layers, interfaces between a living structure and its environment, ensuring metabolism. Toroid forms as well as fractal structures in metazoans can be considered as functionally optimized biological design and attractors in biological morphogenesis. The epithelial surface is an interface between the internal medium of an organism and the outside environmental medium; topological and fractal transformations during metazoan evolution and development increase this interface, ensuring better adaptation of organism to the environment. Fractal structures as well as toroid forms can be considered as a functionally optimized design in Metazoa. Topological methodology reveals a certain set of topological rules constraining and directing biological morphogenesis during evolution and development.",
    url = "https://doi.org/10.4236/am.2014.517255",
    doi = "10.4236/am.2014.517255",
    openalex = "W1977669870",
    references = "isaeva2006topological"
}

@article{doi101007978940179642218,
    author = "Sebé-Pedrós, Arnau and de Mendoza, Alex",
    title = "Transcription Factors and the Origin of Animal Multicellularity",
    year = "2015",
    booktitle = "Advances in Marine Genomics",
    url = "https://www.semanticscholar.org/paper/d0e25719acc6862ba5a75c8f248550d82906652b",
    doi = "10.1007/978-94-017-9642-2\_18",
    is_oa = "true",
    pages = "379-394",
    semanticscholar_citation_count = "20",
    semanticscholar_id = "d0e25719acc6862ba5a75c8f248550d82906652b"
}

@article{s292f7f61b285b0733c8a2106ffce383fca688b92e,
    author = "Ereskovsky, A.",
    title = "Sponge embryology : the past , the present and the future",
    year = "2017",
    url = "https://www.semanticscholar.org/paper/92f7f61b285b0733c8a2106ffce383fca688b92e",
    is_oa = "true",
    semanticscholar_citation_count = "5",
    semanticscholar_id = "92f7f61b285b0733c8a2106ffce383fca688b92e"
}

@article{doi101101802215,
    author = "Tao, Weixin and Cheng, Yanfen and Song, Mi Hye and Weisblat, D. and Kuo, Dian-Han",
    title = "Diversification of metazoan Kexin-like proprotein convertases: insights from the leech Helobdella",
    year = "2019",
    journal = "bioRxiv",
    abstract = "Intercellular communication is quintessential for multicellularity and often mediated by secreted peptide ligands. In Metazoa, proprotein convertases are a major class of endoproteases partaking in the proteolytic processing of these ligands, which is in turn required for their signaling activities. In vertebrates, the best-studied convertase substrates are neuropeptides, peptide hormones, and members of the TGFβ/BMP-family. Each ligand is processed by a particular subset of convertases. Therefore, the diversification of convertases may have contributed to the growing complexity of cellular communication in metazoan evolution. However, proprotein convertases have not been systematically explored in Metazoa. Here, we sampled the representative metazoan genomes and established that six Kexin-like proprotein convertases were present in the last common ancestor of protostomes and deuterostomes. Among these, we identified a novel PCSKX orthologous group (OG) that was lost in vertebrates. Spiralian protosomes have, in general, maintained all six OGs. Therefore, we characterized the functional divergence of the Kexin-like OGs in the leech Helobdella, an experimentally tractable spiralian. Gene expression patterns suggested that PCSK1 and PCSK2 are specialized for the processing of neuropeptides and peptide hormones in bilaterians and that the newly identified PCSKX is probably functionally similar to furin and PCSK7. Finally, we showed that, distinct from the BMP morphogen in vertebrate embryos, the convertase-mediated proteolytic cleavage is not required for the short-range BMP signaling in the dorsoventral patterning of leech ectoderm. Together, our data revealed the complexity of the Kexin-like proprotein convertase gene family and their roles in generating diverse patterns of cellular communication in Metazoa.",
    url = "https://doi.org/10.1101/802215",
    doi = "10.1101/802215",
    is_oa = "true",
    semanticscholar_id = "33760f8af9087d438363ed69a637d6e7699657d6"
}

@article{whittle2019contrasting,
    author = "Whittle, Carrie A. and Extavour, Cassandra G.",
    title = "Contrasting patterns of molecular evolution in metazoan germ line genes",
    year = "2019",
    journal = "BMC Evolutionary Biology",
    url = "https://doi.org/10.1186/s12862-019-1363-x",
    doi = "10.1186/s12862-019-1363-x",
    number = "1",
    openalex = "W2918545771",
    volume = "19",
    references = "doi1010160092867492903176, doi1010160378111990904919, doi101038nature06341, doi101038nature09715, doi101038nrg733, doi10108010635150701472164, doi101093molbevmsm088, doi101093molbevmsw054, doi101093oxfordjournalsmolbeva025957, doi101186147121055113"
}