Phylogenetic placement of the enigmatic parasite, Polypodium hydriforme, within the Phylum CnidariaReport as inadecuate




Phylogenetic placement of the enigmatic parasite, Polypodium hydriforme, within the Phylum Cnidaria - Download this document for free, or read online. Document in PDF available to download.

BMC Evolutionary Biology

, 8:139

First Online: 09 May 2008Received: 04 December 2007Accepted: 09 May 2008

Abstract

BackgroundPolypodium hydriforme is a parasite with an unusual life cycle and peculiar morphology, both of which have made its systematic position uncertain. Polypodium has traditionally been considered a cnidarian because it possesses nematocysts, the stinging structures characteristic of this phylum. However, recent molecular phylogenetic studies using 18S rDNA sequence data have challenged this interpretation, and have shown that Polypodium is a close relative to myxozoans and together they share a closer affinity to bilaterians than cnidarians. Due to the variable rates of 18S rDNA sequences, these results have been suggested to be an artifact of long-branch attraction LBA. A recent study, using multiple protein coding markers, shows that the myxozoan Buddenbrockia, is nested within cnidarians. Polypodium was not included in this study. To further investigate the phylogenetic placement of Polypodium, we have performed phylogenetic analyses of metazoans with 18S and partial 28S rDNA sequences in a large dataset that includes Polypodium and a comprehensive sampling of cnidarian taxa.

ResultsAnalyses of a combined dataset of 18S and partial 28S sequences, and partial 28S alone, support the placement of Polypodium within Cnidaria. Removal of the long-branched myxozoans from the 18S dataset also results in Polypodium being nested within Cnidaria. These results suggest that previous reports showing that Polypodium and Myxozoa form a sister group to Bilateria were an artifact of long-branch attraction.

ConclusionBy including 28S rDNA sequences and a comprehensive sampling of cnidarian taxa, we demonstrate that previously conflicting hypotheses concerning the phylogenetic placement of Polypodium can be reconciled. Specifically, the data presented provide evidence that Polypodium is indeed a cnidarian and is either the sister taxon to Hydrozoa, or part of the hydrozoan clade, Leptothecata. The former hypothesis is consistent with the traditional view that Polypodium should be placed in its own cnidarian class, Polypodiozoa.

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2148-8-139 contains supplementary material, which is available to authorized users.

An erratum to this article is available at http:-dx.doi.org-10.1186-1471-2148-9-165.

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Author: Nathaniel M Evans - Alberto Lindner - Ekaterina V Raikova - Allen G Collins - Paulyn Cartwright

Source: https://link.springer.com/article/10.1186/1471-2148-8-139







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