New deep-sea species of Xenoturbella and the position of Xenacoelomorpha

TitleNew deep-sea species of Xenoturbella and the position of Xenacoelomorpha
Publication TypeJournal Article
Year of Publication2016
AuthorsRouse GW, Wilson NG, Carvajal J.I, Vrijenhoek RC
Date Published2016/02
Type of ArticleArticle
ISBN Number0028-0836
Accession NumberWOS:000369304500039
Keywordsanimal phylogeny; bocki phylum xenoturbellida; Deuterostomes; genome; indicate; Mitochondrial; phylogenetic analysis; program; sequence; sister; uncertain

The discovery of four new Xenoturbella species from deep waters of the eastern Pacific Ocean is reported here. The genus and two nominal species were described from the west coast of Sweden(1,2), but their taxonomic placement remains unstable(3,4). Limited evidence placed Xenoturbella with molluscs(5,6), but the tissues can be contaminated with prey(7,8). They were then considered deuterostomes(9-13). Further taxon sampling and analysis have grouped Xenoturbella with acoelomorphs (= Xenacoelomorpha) as sister to all other Bilateria (= Nephrozoa)(14,15), or placed Xenacoelomorpha inside Deuterostomia with Ambulacraria (Hemichordata + Echinodermata)(16). Here we describe four new species of Xenoturbella and reassess those hypotheses. A large species (> 20 cm long) was found at cold-water hydrocarbon seeps at 2,890 m depth in Monterey Canyon and at 1,722 m in the Gulf of California (Mexico). A second large species (similar to 10 cm long) also occurred at 1,722 m in the Gulf of California. The third large species (similar to 15 cm long) was found at similar to 3,700 m depth near a newly discovered carbonate-hosted hydrothermal vent in the Gulf of California. Finally, a small species (similar to 2.5 cm long), found near a whale carcass at 631 m depth in Monterey Submarine Canyon (California), resembles the two nominal species from Sweden. Analysis of whole mitochondrial genomes places the three larger species as a sister clade to the smaller Atlantic and Pacific species. Phylogenomic analyses of transcriptomic sequences support placement of Xenacoelomorpha as sister to Nephrozoa or Protostomia.

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