Evidence for a clade of nematodes, arthropods and other moulting animals

  title={Evidence for a clade of nematodes, arthropods and other moulting animals},
  author={Anna Marie A. Aguinaldo and James M. Turbeville and Lawrence S. Linford and Maria C. Rivera and James R. Garey and Rudolf A. Raff and James Alan Lake},
The arthropods constitute the most diverse animal group, but, despite their rich fossil record and a century of study, their phylogenetic relationships remain unclear1. Taxa previously proposed to be sister groups to the arthropods include Annelida, Onychophora, Tardigrada and others, but hypotheses of phylogenetic relationships have been conflicting2,3. For example, onychophorans, like arthropods, moult periodically, have an arthropod arrangement of haemocoel1,4, and have been related to… 

The position of arthropods in the animal kingdom: a search for a reliable outgroup for internal arthropod phylogeny.

A cladistic approach to metazoan evolution including 133 18S rDNA sequences of 31 animal phyla is reported, suggesting that the Bilateria and Protostomia are monophyletic.

Palaeontological and Molecular Evidence Linking Arthropods, Onychophorans, and other Ecdysozoa

Analysis of DNA sequences from many genes together with morphological characters involving the cuticle and its molting strengthen the grouping of cycloneuralian worms and arthropods as Ecdysozoa, identify the velvet worms (Phylum Onychophora) as the closest living relatives of arthropoda, and interpret segmentation as having separate evolutionary origins in arthropod and annelid worms.

Reevaluating the arthropod tree of life.

Monophyly of Pycnogonida, Euchelicerata, Myriapoda, Tetraconata, and Hexapoda is well supported, but the interrelationships of arachnid orders and the details of crustacean paraphyly with respect to Hexapda remain the major unsolved phylogenetic problems.

Ecdysozoan Mitogenomics: Evidence for a Common Origin of the Legged Invertebrates, the Panarthropoda

Phylogenetic analyses based on concatenated amino acid coding sequences support a monophyletic origin of the Ecdysozoa and the position of Priapulida as the sister group of a monophysletic Panarthropoda (Tardigrada plus Onychophora plus Arthropoda).

MicroRNAs and phylogenomics resolve the relationships of Tardigrada and suggest that velvet worms are the sister group of Arthropoda

The study confirms the monophyly of the legged ecdysozoans, shows that past support for a Tardigrada + Nematoda group was due to long-branch attraction, and suggests that the velvet worms are the sister group to the arthropods.

The Articulata hypothesis – or what is a segment?

Based on numerous similarities not shared with other bilaterian taxa it is suggested that segmentation of annelids and arthropods is homologous and apomorphic for a monophyletic Articulata.

Coelomata and not Ecdysozoa: evidence from genome-wide phylogenetic analysis.

A phylogenetic analysis of over 500 sets of orthologous proteins, which are represented in plants, animals, and fungi, using maximum likelihood, maximum parsimony, and distance methods showed concordance between evolution of protein sequences and higher-level evolutionary events, such as domain fusion or gene loss.

A comprehensive molecular phylogeny of tardigrades—adding genes and taxa to a poorly resolved phylum‐level phylogeny

Eutardigrade superfamilies recently proposed by Sands and collaborators in the order Parachela were tested with the introduction of new sequences from additional genera, and the possible morphological synapomorphies supporting those superfam families are discussed.

The position of the Arthropoda in the phylogenetic system

There are morphological characters that support Articulata, but molecular as well as morphological data advocate Ecdysozoa, and comparative morphology suggests Gastrotricha as the sister group of Ecdy sozoa with the synapomorphies.

The position of arthropods in the animal kingdom: Ecdysozoa, islands, trees, and the "Parsimony ratchet".

The goal of this paper was to investigate the position of the Arthropoda within the protostome animals and determine arthropod sister-group relationships, and the phylogenetic conclusions were summarized as monophyletic.



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.

Evidence from 12S ribosomal RNA sequences that onychophorans are modified arthropods.

Parsimony analysis suggests that onychophorans form a sister group to chelicerates and crustaceans plus hexapods, but this relationship is not well supported by monophyly testing, which conflict with current hypotheses of evolutionary pathways within arthropods.

A Cladistic Analysis of Pseudocoelomate (Aschelminth) Morphology

It is concluded that there are 2 main lines of pseudocoelomate evolution: a minor clade (Acanthocephala + Rotifera) defined principally by a syncytial epidermis, intracytoplasmic lamina, and sperms with anterior flagella, and a major clade, defined primarily by a cuticle that is molted.

Deducing the pattern of arthropod phytogeny from mitochondrial DNA rearrangements

THE origins of arthropods and the phylogenetic relationships among their three major living groups (atelocerates, crustaceans and chelicerates) are vigorously contended. To help resolve this, we

Bilaterians of the Precambrian-Cambrian transition and the annelid-arthropod relationship.

  • J. W. Valentine
  • Environmental Science
    Proceedings of the National Academy of Sciences of the United States of America
  • 1989
There is no evidence that Late Proterozoic invertebrates possessed a coelom suited for peristaltic burrowing, therefore, the annelidan body plan had probably not appeared, and it is not implausible, however, that coelomic spaces in the form of ducts or organ sacs were present in segmented segmented forms.


The achievements and controversies between molecular studies are reviewed and compared to corresponding studies based on morphological data, and important methodological considerations that affect the studies of phylum-level relationships are considered.

The early emergence of platyhelminths is contradicted by the agreement between 18S rRNA and Hox genes data.

  • G. Balavoine
  • Biology
    Comptes rendus de l'Academie des sciences. Serie III, Sciences de la vie
  • 1997

Arthropod Phylogeny with Special Reference to Insects

Elucidates the major evolutionary pathways of the Phylum Arthropoda, based on the phylogenetic method of Hennig, and focuses on discovering the derived character states that most probably had a common origin in an ancestral state.

18S rRNA data indicate that Aschelminthes are polyphyletic in origin and consist of at least three distinct clades.

Analyses of 18S rRNA sequences from six Aschelminth phyla (including four previously unpublished sequences) support polyphyly for the Aschelminthes.

Molecular phylogeny of the animal kingdom.

A rapid sequencing method for ribosomal RNA was applied to the resolution of evolutionary relationships among Metazoa, finding that coelomates radiated rapidly into four groups: chordates, echinoderms, arthropods, and eucoelomate protostomes.