Hemichordate Relationships and Insights into Ancestors

Meeting Abstract

P1.26  Thursday, Jan. 3  Hemichordate Relationships and Insights into Ancestors CANNON, JT*; RYCHEL, AL; SWALLA, BJ; HALANYCH, KM; Auburn University, Auburn AL; University of Washington, Seattle; University of Washington, Seattle; Auburn University, Auburn AL cannojt@auburn.edu

The phylogenetic relationships within Hemichordata are significant for understanding the evolution of the deuterostomes, the evolution of the recently proposed clade Xenambulacraria (Echindodermata, Hemichordata and Xenoturbellida), and the origin of the chordates. At present, Hemichordata is divided into two classes, the solitary, free-living Enteropneusta worms, and the colonial, tube-dwelling Pterobranchia. Both classes have been implicated in a number of hypotheses regarding the early evolution of the deuterostomes, and have very different larval and adult body plans. Elucidating the phylogenetic relationships within the hemichordates is therefore critical to further investigations of these hypotheses. Previous molecular phylogenetic studies of hemichordates using 28S rDNA data or 18S rDNA data have suggested that the enteropneusts are either monophyletic or paraphyletic, respectively. Here, we greatly increase the number of hemichordate species used in the analyses, including never before analyzed deep sea enteropneusts, and tornaria larvae from the Gulf Stream. Using mitochondrial 16S and cytB sequences as well as 18s rDNA and 28S rDNA data, our preliminary phylogenetic analyses show enteropneust families forming monophyletic clades, although the monophyly of a few genera is in question. The adult deep sea species groups with the tornaria larvae from the Gulf Stream, as a clade within Ptychoderidae. Implications of these phylogenetic results for the evolution of deuterostome body plans will be discussed.

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