Unsegmented Annelids? Possible Origins of Four Lophotrochozoan Worm Taxa1

  title={Unsegmented Annelids? Possible Origins of Four Lophotrochozoan Worm Taxa1},
  author={Kenneth M. Halanych and Thomas G. Dahlgren and Damhnait McHugh},
  booktitle={Integrative and comparative biology},
Abstract In traditional classification schemes, the Annelida consists of the Polychaeta and the Clitellata (the latter including the Oligochaeta and Hirudinida). However, recent analyses suggest that annelids are much more diverse than traditionally believed, and that polychaetes are paraphyletic. Specifically, some lesser-known taxa (previously regarded as separate phyla) appear to fall within the annelid radiation. Abundant molecular, developmental, and morphological data show that the… 

Annelid phylogeny and the status of Sipuncula and Echiura

Using multiple genes and explicit hypothesis testing, it is shown that Echiura, Siboglinidae, and Clitellata are derived annelid with polychaete sister taxa, and that Sipuncula should be included within annelids.

Phylogeny of Annelida

The phylogeny of Annelida was split into two major clades, one clade adapted to an errant mobile life and the other which includes earthworms and leeches, to a more sessile, sedentary one.

Molecular phylogeny of siboglinid annelids (a.k.a. pogonophorans) : a review

The literature to date on siboglinid molecular phylogeny is reviewed and a summary of the clade’s evolution is summarized.

Current status of annelid phylogeny

The new annelids phylogeny highlights the variability and lability of annelid body plans, and many instances of simplifications of body plan as adaptations to new life styles can be found.

Systematics, evolution and phylogeny of Annelida – a morphological perspective

Attempts to understand the major transitions in annelid evolution are reviewed and discussed in the light of new morphological evidence such as photoreceptor cell and eye evolution as well as the evolution of the nervous system and musculature.

The impact of fossil data on annelid phylogeny inferred from discrete morphological characters

A reinvestigation of the morphology of key fossil taxa is presented and analyses using probabilistic methods and both equal- and implied-weights parsimony recover paraphyletic polychaetes and support the conclusion that echiurans and clitellates are derived polychaETes.

MicroRNAs resolve an apparent conflict between annelid systematics and their fossil record

It is shown that annelids are monophyletic with respect to sipunculans, and polychaetes are paraphyleticwith respect to the clitellate Lumbricus, conclusions that are consistent with the fossil record.

Polychaete phylogeny based on morphological data – a comparison of current attempts

There is at least strong support for the Annelida as wells as for several of its taxa above the level of traditional families; the monophyly of the Polychaeta, however, remains questionable.

Polychaete phylogeny based on morphological data — a comparison of current attempts

There is at least strong support for the Annelida as wells as for several of its taxa above the level of traditional families; the monophyly of the Polychaeta, however, remains questionable.

Phylogenomics of tubeworms (Siboglinidae, Annelida) and comparative performance of different reconstruction methods

Every analysis conducted herein strongly supported Osedax being most closely related to the Vestimentifera and Sclerolinum clade, rather than Frenulata, as previously reported, and the alternative hypothesis that frenulates andOsedax are sister groups to one another was explicitly rejected by an approximately unbiased (AU) test.



Myzostomida: a link between trochozoans and flatworms?

All analyses congruently indicated that myzostomids are not annelids but suggested instead that they are more closely related to flatworms than to any trochozoan taxon, which has significant implications for understanding the evolution of metazoan body plans.

Molecular evidence that echiurans and pogonophorans are derived annelids.

  • D. McHugh
  • Biology
    Proceedings of the National Academy of Sciences of the United States of America
  • 1997
This result, indicating the derived loss of segmentation in echiurans, has profound implications for the understanding of the evolution of metazoan body plans and challenges the traditional view of the phylum-level diversity and evolutionary relationships of protostome worms.

Molecular phylogeny of the Annelida

Both molecular and morphological analyses support placement of the Siboglinidae (formerly the Pogonophora) as a derived group within the Annelida; there is also evidence, based on molecular analysis of the nuclear gene elongation factor-1α, that the unsegmented echiurids are derived annelids.

The articulation of annelids

The Annelida should not be used unless relationships within the Articulata are resolved to show it is a monophyletic taxon, and the Pogonophora should revert to the original family name Lamellisabellidae Uschakov, 1933.

Systematization of the Annelida: different approaches

The main message from phylogenetic analyses of molecular data is that there is no evidence for a monophyletic Polychaeta; instead, placement of the clitellates, pogonophorans and echiurans within the polychaete clade is supported, rendering thePolychaeta paraphyletic.

Molecular Evidence that Sclerolinum brattstromi Is Closely Related to Vestimentiferans, not to Frenulate Pogonophorans (Siboglinidae, Annelida)

Evidence from the 18S nuclear rDNA gene and the 16S mitochondrial r DNA gene presented here shows that Sclerolinum is the sister clade to vestimentiferans although it lacks the characteristic morphology (i.e., a vestimentum).

Myzostomida Are Not Annelids: Molecular and Morphological Support for a Clade of Animals with Anterior Sperm Flagella

A phylogenetic analysis of 18S and 28S ribosomal DNA sequence data of Myzostoma glabrum is presented to show that myzostomes are a sister group of the Cycliophora, closely related to the rotifer‐acanthocephalan clade (=Syndermata).

Annelida and Arthropoda are Not Sister Taxa: A Phylogenetic Analysis of Spiralian Metazoan Morphology

This study presents a new analysis of 141 independently assembled characters, purported to represent the current state of knowledge of metazoan morphology and embryology, and results in robust support of the Eutrochozoa hypothesis.

Mitochondrial genomes of Galathealinum, Helobdella, and Platynereis: sequence and gene arrangement comparisons indicate that Pogonophora is not a phylum and Annelida and Arthropoda are not sister taxa.

Comparisons of relative gene arrangements and of the nucleotide and inferred amino acid sequences among these and other published taxa provide strong support for an annelid-mollusk clade that excludes arthropods, and for the inclusion of pogonophorans within Annelida, rather than giving them separate phylum status.

The phylogenetic position of the Clitellata and the Echiura - on the problematic assessment of absent characters*

Evidence is presented that in both taxa these absent characters represent derived, apomorphic character states and the consequences for their phylogenetic position and the questionable monophyly of the Polychaeta are discussed.