Relations of the new phylum Cycliophora


The Cycliophora is the most recently described animal phylum and is based on a single species, Symbion pandora, which was discovered on the mouthparts of the Norway lobster Nephrops norvegicus1. Because only a few morphological data1,2,3 are available for Symbion, the precise nature of its phylogenetic relationships is highly controversial2,4,5. Here we present a phylogenetic analysis of 18S ribosomal RNA sequence data, including a new Symbion sequence, which places Symbion in a lophophorate-aschelminth-protostome clade and which suggests a sister-group relationship between Cycliophora and a Rotifera-Acanthocephala clade.

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Figure 1: Strict consensus tree, showing groups present in all trees obtained by four different tree-construction methods applied to an 18S rRNA data set6 that includes the S. pandora and N. norvegicus data.


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Winnepenninckx, B., Backeljau, T. & Kristensen, R. Relations of the new phylum Cycliophora. Nature 393, 636–638 (1998).

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