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The chaetognaths, or arrowworms, constitute a small and enigmatic phylum of marine invertebrates whose phylogenetic affinities have long been uncertain. A popular hypothesis is that the chaetognaths are the sister group of the major deuterostome phyla: chordates, hemichordates, and echinoderms. Here we attempt to determine the affinities of the chaetognaths by using molecular sequence data. We describe the isolation and nucleotide sequence determination of 18S ribosomal DNA from one species of chaetognath and one acanthocephalan. Extensive phylogenetic analyses employing a suite of phylogenetic reconstruction methods (maximum parsimony, maximum likelihood, evolutionary parsimony, and two distance methods) suggest that the hypothesized relationship between chaetognaths and the deuterostomes is incorrect. In contrast, we propose that the lineage leading to the chaetognaths arose prior to the advent of the coelomate metazoa.

Original publication

DOI

10.1093/oxfordjournals.molbev.a040030

Type

Journal article

Journal

Mol Biol Evol

Publication Date

05/1993

Volume

10

Pages

660 - 676

Keywords

Animals, Base Sequence, DNA, Ribosomal, Invertebrates, Molecular Sequence Data, Oligodeoxyribonucleotides, Phylogeny, Polymerase Chain Reaction, Probability, RNA, Ribosomal, 18S, Seawater, Zooplankton