Are the Platyhelminthes a monophyletic primitive group? An assessment using 18S rDNA sequences.

@article{Carranza1997AreTP,
  title={Are the Platyhelminthes a monophyletic primitive group? An assessment using 18S rDNA sequences.},
  author={Salvador Carranza and Jaume Bagu{\~n}{\'a} and Marta Riutort},
  journal={Molecular biology and evolution},
  year={1997},
  volume={14 5},
  pages={
          485-97
        }
}
In most zoological textbooks, Platyhelminthes are depicted as an early-emerging clade forming the likely sister group of all the other Bilateria. Other phylogenetic proposals see them either as the sister group of most of the Protostomia or as a group derived from protostome coelomate ancestors by progenesis. The main difficulty in their correct phylogenetic placing is the lack of convincing synapomorphies for all Platyhelminthes, which may indicate that they are polyphyletic. Moreover, their… 

Figures and Tables from this paper

Molecular phylogeny of the Platyhelminthes
TLDR
Phylum-wide analyses based on complete ribosomal and other nuclear genes addressed to answer the main issues facing systematics and phylogeny of Platyhelminthes are reviewed.
The interrelationships of all major groups of Platyhelminthes: phylogenetic evidence from morphology and molecules
TLDR
It is stressed that morphological and molecular data in some respects lead to contradictory results, for instance concerning the position of the Fecampiidae/Urastoma/Ichthyophaga and the relative position ofThe Lecithoepitheliata.
The Nemertodermatida are basal bilaterians and not members of the Platyhelminthes
TLDR
The results imply that the last common ancestor of bilaterian metazoans was a small, benthic, direct developer without segments, coelomic cavities, nephrida or a true brain.
A Molecular Test of Platyhelminth Phylogeny: Inferences from Partial 28S rDNA Sequences
TLDR
Nucleotide sequences of the region extending from the D3 to the D6 expansion segments of the 28S rDNA gene were used to reconstruct evolutionary relationships within the Platyhelminthes, and it is tentatively concluded that the immediate sister group of Neodermata is Fecampiida.
A robust molecular phylogeny of the Tricladida (Platyhelminthes: Seriata) with a discussion on morphological synapomorphies
TLDR
The results show that the Maricola is monophyletic and is the primitive sister group to the rest of the Tricladida (the Paludicola plus the Terricola), which is suggested to be a new clade, the Continenticola, which comprises the families Dugesiidae, Planariidae, Dendrocoelidae and the terricola.
Gnathostomulida--an enigmatic metazoan phylum from both morphological and molecular perspectives.
TLDR
The molecular data supported more strongly a third possible relationship with the gnathostomulids as a member of the Nematoda + Chaetognatha clade and called for a reevaluation of the morphological data and a denser sampling of the lesser phyla.
A REAPPRAISAL OF THE PHYLOGENETIC AND TAXONOMIC POSITION OF LAND PLANARIANS (PLATYHELMINTHES, TURBELLARIA, TRICLADIDA) INFERRED FROM 18S RDNA SEQUENCE S
Land planarians belong to the suborder Tricladida within which four infraorders are currently recognized: the Maricola, the Cavernicola, the Paludicola and the Terricola (land planarians).
Phylogeny of the Nemertodermatida (Acoelomorpha, Platyhelminthes). A cladistic analysis
TLDR
The phylogeny of the Nemertodermatida was estimated using paup 4.0 software for parsimony analysis based on 72 structural parsimony‐informative characters totalling 184 different character states, with a single most parsimonious tree obtained with 140 steps and a consistency index of 0.80.
...
...

References

SHOWING 1-10 OF 71 REFERENCES
The phylogenetic status of arthropods, as inferred from 18S rRNA sequences.
TLDR
It is suggested that a previous study's inference of the Arthropoda as paraphyletic may be the result of having two few arthropod taxa available for analysis and including long-branched taxa, and that the evolutionary-parsimony method, like distance and parsimony, may be biased by taxa with long branches.
Phylogenetic position of phylum Nemertini, inferred from 18S rRNA sequences: molecular data as a test of morphological character homology.
TLDR
The molecular inference corroborates recent morphological character analyses that reveal no synapomorphies of nemertines and flatworms but instead suggest that the circulatory system and rhynchocoel of nemERTines are homologous to coelomic cavities of protostome coelomates, thus supporting the corresponding hypothesis that nemertine belong within a protostomate-coelomate clade.
Phylogenetic position of the dicyemid mesozoa inferred from 18S rDNA sequences.
TLDR
The present results favor the hypothesis that the dicyemids do not represent an early divergent metazoan group, but rather a group degenerated from a triploblastic ancestor.
Phylogenetic position of Acoel turbellarians inferred from partial 18S rDNA sequences.
TLDR
The deduced phylogenetic tree suggests that the three groups examined form discrete and separate entities, and suggests an earlier emergence of the Acoel turbellarians than the other platyhelminths.
Evidence that two types of 18S rDNA coexist in the genome of Dugesia (Schmidtea) mediterranea (Platyhelminthes, Turbellaria, Tricladida).
TLDR
The 1st case of 18S rDNA polymorphism within a metazoan species is reported and the need for analyzing a large number of clones whenever 18S sequences obtained by PCR amplification and cloning are being used in phylogenetic reconstruction is stressed.
An analysis of the origin of metazoans, using comparisons of partial sequences of the 28S RNA, reveals an early emergence of triploblasts.
TLDR
Compared sequences from the 5′ end of the large subunit ribosomal RNA of a number of protists, fungi, plants and metazoans, including all diploblastic phyla, showed a much more ancient origin of triploblasts with respect to diplobasts than classically assumed.
Details of the evolutionary history from invertebrates to vertebrates, as deduced from the sequences of 18S rDNA.
  • H. Wada, N. Satoh
  • Biology
    Proceedings of the National Academy of Sciences of the United States of America
  • 1994
TLDR
Phylogenetic comparisons of the sequences of 18S rDNA suggest the monophyly of the deuterostomes, with the exception of the chaetognaths, and support the hypothesis that chordates evolved from free-living ancestors.
The phylogenetic position of the Aspidobothrea within the parasitic flatworms inferred from ribosomal RNA sequence data.
  • D. Blair
  • Biology
    International journal for parasitology
  • 1993
...
...