Tardigrade phylogeny: Congruency of morphological and molecular evidence

The 18S rRNA gene sequences from two tardigrades were analyzed with previou sly published sequences from four other tardigrades and a variety of metazo ans. Phylogenetic analysis confirms that tardigrades are associated with ar thropods and that 18S rRNA gene phylogeny is consistent with morphology-bas ed hypotheses of tardigrade evolutionary relationships. Thulinia and Hypsib ius group together as sister taxa to Macrobiotus, forming the order Parache la, which in turn is a sister group to Milnesium, a representative of the o rder Apochela. Together, Parachela and Apochela form a sister group to Echi niscus, a heterotardigrade that appears in the analysis as the most basal t ardigrade.