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

The arthropods constitute the most diverse animal group, but, despite their rich fossil record and a century of study, their phylogenetic relationships remain unclear. Taxa previously proposed to be sister groups to the arthropods include Annelida, Onychophora, Tardigrada and others, but hypotheses...

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Published in:Nature (London) 1997-05, Vol.387 (6632), p.489-493
Main Authors: Aguinaldo, Anna Marie A, Turbeville, James M, Linford, Lawrence S, Rivera, Maria C, Garey, James R, Raff, Rudolf A, Lake, James A
Format: Article
Language:English
Subjects:
Animals
Arthropoda
Arthropods - classification
Arthropods - genetics
Biological and medical sciences
Biological Evolution
Biology
Deoxyribonucleic acid
DNA
Fundamental and applied biological sciences. Psychology
Genetics of eukaryotes. Biological and molecular evolution
Insects
Marine
Molecular Sequence Data
Nematoda
Nematoda - classification
Nematoda - genetics
Phylogeny
RNA, Ribosomal, 18S - genetics
Worms
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Summary:The arthropods constitute the most diverse animal group, but, despite their rich fossil record and a century of study, their phylogenetic relationships remain unclear. Taxa previously proposed to be sister groups to the arthropods include Annelida, Onychophora, Tardigrada and others, but hypotheses of phylogenetic relationships have been conflicting. For example, onychophorans, like arthropods, moult periodically, have an arthropod arrangement of haemocoel, and have been related to arthropods in morphological and mitochondrial DNA sequence analyses. Like annelids, they possess segmental nephridia and muscles that are a combination of smooth and obliquely striated fibres. Our phylogenetic analysis of 18S ribosomal DNA sequences indicates a close relationship between arthropods, nematodes and all other moulting phyla. The results suggest that ecdysis (moulting) arose once and support the idea of a new clade, Ecdysozoa, containing moulting animals: arthropods, tardigrades, onychophorans, nematodes, nematomorphs, kinorhynchs and priapulids. No support is found for a clade of segmented animals, the Articulata, uniting annelids with arthropods. The hypothesis that nematodes are related to arthropods has important implications for developmental genetic studies using as model systems the nematode Caenorhabditis elegans and the arthropod Drosophila melanogaster, which are generally held to be phylogenetically distant from each other.
ISSN:0028-0836
1476-4687
DOI:10.1038/387489a0