NICHOLS, P. Brent; NELSON, Diane R; GAREY, James R; University of South Florida; East Tennessee State University; University of South Florida: A Family level Analysis of Tardigrade Phylogeny

There is currently no overall phylogenetic hypothesis of tardigrade evolution in the literature. This study developed a morphological data set suitable for phylogenetic analysis at the family level. A data matrix consisting of 50 characters for 15 families of Tardigrada was analyzed by maximum parsimony. Ground pattern characters for tardigrades were established from the literature and Kinorhynchs, loriciferans, and gastrotrichs were used as outgroups. The results agree with the currently accepted hypothesis that Eutardigrada and Heterotardigrada are each monophyletic groups. Among the eutardigrades, Eohypsibiidae was found to be a sister group to Macrobiotidae + Hypsibiidae. Necopinatidae appears to be basal among the Parachaela while Milnesiidae was the basal eutardigrade. Among the heterotardigrades the family Oreellidae appears to be basal, while Coronarctidae + Batillipedidae were found be sister groups to Echiniscoidea + Echiniscidae. Therefore, neither Arthrotardigrada nor Echiniscoidea appear to be monophyletic. The 18S rRNA gene sequence of Batillipes muris was obtained and its addition to a previously published dataset supports the monophyly of Heterotardigrada. This analysis of the morphological data set suggests that 18S rRNA sequences from members of Oreellidae, Renaudarctidae, and Halechiscidae would be useful to test the paraphyletic and polyphyletic groups that were recovered among the Heterotardigrada.