Phylogeny of gastrotricha: a morphology-based framework of gastrotrich relationships

Currently, the phylum Gastrotricha is divided into the orders Macrodasyida and Chaetonotida, with the structure of the myoepithelial pharynx being an important distinguishing feature. Macrodasyida currently has six recognized families, and Chaetonotida comprises seven families. However, within-group relationships are poorly understood. To arrive at a better understanding o f gastrotrich systematics and phylogeny, we performed the first cladistic a nalysis of nearly all known gastrotrich genera using 71 morphological chara cters. Results suggest that the Gastrotricha is a monophyletic group (suppo rted by 82% of bootstrap replications) with its most primitive taxa distrib uted among the families Dactylopodolidae and Neodasyidae, Monophyly of Macr odasyida and Chaetonotida was supported by 90% and 52% bootstrap replicatio ns, respectively. Within the Macrodasyida, the families Dactylopodolidae, T urbanellidae, Macrodasyidae, and Thaumastodermatidae all formed monophyleti c clades. The families Planodasyidae and Lepidodasyidae were paraphyletic. Among the Chaetonotida, the marine family Xenotrichulidae was monophyletic, supported by 51% of bootstrap replications. A second clade containing all freshwater families was supported by 62% bootstrap values. However, Chaeton otidae were paraphyletic. Using this analysis as a framework, we now can ex plore possible patterns of evolution within it, and arrive at a consensus o f the gastrotrich ground pattern. Moreover, in future molecular studies of metazoan phylogeny, we will be able to select gastrotrich species that are more appropriate representatives of the phylum.