⃛and molluscan embryogenesis

Israelsson, Olle

doi:10.1038/36246

Cited by 42 publications

(25 citation statements)

References 2 publications

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“…Eggs and embryos in Xenoturbella (Israelsson, 1997(Israelsson, , 1999Israelsson and Budd, 2005) posesses several protostome features, in particular a non-radial cleavage, the absence of cortical reaction during fertilization, and the ciliary ultrastructure. There are, on the other hand, possible similarities in constitution to echinoderm oocytes.…”

Section: Discussionmentioning

confidence: 99%

“…Histological data (Westblad, 1949) suggested Xenoturbella to be a new taxon within the Acoelomorpha, a hypothesis that was later supported by ultrastructural features of the epidermal cilia (Franzén and Afzelius, 1987;Rohde et al, 1988;Rieger et al, 1991;Lundin, 1998). Other morphological (Ehlers, 1991), ontogenetic (Israelsson, 1997(Israelsson, , 1999Israelsson and Budd, 2005), and ultrastructural features (Raikova et al, 2000), however, casted serious doubt on the acoelomorpha hypothesis. Instead, Xenoturbella was variably grouped to enteropneusts or holothurians (Reisinger, 1960), to bryozoans (Zrzavy et al, 1998), and to molluscs (Israelsson, 1997(Israelsson, , 1999.…”

Section: Introductionmentioning

confidence: 99%

“…Other morphological (Ehlers, 1991), ontogenetic (Israelsson, 1997(Israelsson, , 1999Israelsson and Budd, 2005), and ultrastructural features (Raikova et al, 2000), however, casted serious doubt on the acoelomorpha hypothesis. Instead, Xenoturbella was variably grouped to enteropneusts or holothurians (Reisinger, 1960), to bryozoans (Zrzavy et al, 1998), and to molluscs (Israelsson, 1997(Israelsson, , 1999. The immunoreactivity of X. bocki nerve cells to antibodies raised against echinoderm neuropeptides suggested a close phylogenetic relationship to Ambulacraria (Stach et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

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The mitochondrial DNA of Xenoturbella bocki: genomic architecture and phylogenetic analysis

et al. 2007

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The phylogenetic position of Xenoturbella bocki has been a matter of controversy since its description in 1949. We sequenced a second complete mitochondrial genome of this species and performed phylogenetic analyses based on the amino-acid sequences of all 13 mitochondrial proteincoding genes and on its gene order. Our results confirm the deuterostome relationship of Xenoturbella. However, in contrast to a recently published study [Bourlat et al., Nature 444: 85-88 (2006)], our data analysis suggests a more basal branching of Xenoturbella within the deuterostomes, rather than a sister-group relationship to the Ambulacraria (Hemichordata and Echinodermata).

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The mitochondrial DNA of Xenoturbella bocki: genomic architecture and phylogenetic analysis

et al. 2007

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“…We have also looked for these code changes in two enigmatic taxa sometimes allied to the Platyhelminthes-Xenoturbella (11,12) and the dicyemid mesozoan Dicyema misakiense (13). Studies of oogenesis (14) and Cox I and 18S rDNA data (15) have previously contradicted a platyhelminth affinity for Xenoturbella. 18S rDNA studies of Mesozoa were ambiguous because of long branch effects (13), but the presence of a lophotrochozoan type Hox gene in D. misakiense (16) has led to support for a derived (and hence potentially f latworm) position for this latter phylum rather than the basal position outside the triploblasts otherwise espoused (17).…”

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confidence: 99%

Changes in mitochondrial genetic codes as phylogenetic characters: Two examples from the flatworms

Telford

Herniou

Russell

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

229

122

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Shared molecular genetic characteristics other than DNA and protein sequences can provide excellent sources of phylogenetic information, particularly if they are complex and rare and are consequently unlikely to have arisen by chance convergence. We have used two such characters, arising from changes in mitochondrial genetic code, to define a clade within the Platyhelminthes (flatworms), the Rhabditophora. We have sampled 10 distinct classes within the Rhabditophora and find that all have the codon AAA coding for the amino acid Asn rather than the usual Lys and AUA for Ile rather than the usual Met. We find no evidence to support claims that the codon UAA codes for Tyr in the Platyhelminthes rather than the standard stop codon. The Rhabditophora are a very diverse group comprising the majority of the free-living turbellarian taxa and the parasitic Neodermata. In contrast, three other classes of turbellarian flatworm, the Acoela, Nemertodermatida, and Catenulida, have the standard invertebrate assignments for these codons and so are convincingly excluded from the rhabditophoran clade. We have developed a rapid computerized method for analyzing genetic codes and demonstrate the wide phylogenetic distribution of the standard invertebrate code as well as confirming already known metazoan deviations from it (ascidian, vertebrate, echinoderm͞hemichordate).

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“…Their phylogenetic analyses of these sequences clearly indicated a link with the Lophotrochozoa (SSU) or more specifically the bivalve molluscs (Cox1). Corroborating this finding, the second article described a phylogenetic analysis based on a specific characteristic of oocyte morphology shared by Xenoturbella and Protobranch molluscs; the persistence through vitellogenesis of micronucleoli arranged along one side of the germinal vesicle (Israelsson, 1997). In a subsequent article, Israelsson described in great detail the presence within Xenoturbella of developmental stages of typical molluscan pericalymma larvae (Israelsson, 1999).…”

Section: Introductionmentioning

confidence: 99%

Xenoturbellida: The fourth deuterostome phylum and the diet of worms

Telford

2008

Genesis

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Since the discovery of the marine worm Xenoturbella bocki in 1915 by Sixten Bock and its first published description by Einar Westblad (Westblad,1949, Arkiv Zoologi 1:3–29), Xenoturbella was generally allied to the turbellarian flatworms, perhaps most closely to acoelomorphs. In 1997, however, analyses of ribosomal DNA (Norén and Jondelius, 1997, Nature 390:31–32) and developing oocytes (Israelsson, 1997, Nature 390:32) [and, subsequently, embryos (Israelsson, 1999, Proc R Soc Lond B 266:835–841)] recovered from Xenoturbella specimens led to the surprising conclusion that it was in fact a highly degenerate bivalve mollusc. Bourlat et al. showed in 2003 that this result was due to contamination from bivalves in its diet (Bourlat et al.,2003, Nature 424:925–928). Our analyses showed Xenoturbella is a deuterostome, related to the Ambulacraria (echinoderms and hemichordates). Subsequent work has shown that Xenoturbellida is a separate lineage from the Ambulacraria and therefore constitutes the fourth deuterostome phylum (Bourlat et al.,2006, Nature 444:85–88). I consider this phylogenetic position in the light of what is known of its genetics, morphology, and ontogeny. I examine what this phylogenetic position for Xenoturbella can tell us about its own evolution and what light this might shine on the common ancestor of the deuterostomes and hence on the origins of the chordates. genesis 46:580–586, 2008. © 2008 Wiley‐Liss, Inc.

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⃛and molluscan embryogenesis

Cited by 42 publications

References 2 publications

The mitochondrial DNA of Xenoturbella bocki: genomic architecture and phylogenetic analysis

The mitochondrial DNA of Xenoturbella bocki: genomic architecture and phylogenetic analysis

Changes in mitochondrial genetic codes as phylogenetic characters: Two examples from the flatworms

Xenoturbellida: The fourth deuterostome phylum and the diet of worms

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