Tardigrade Evolutionary Relationships

Nichols, P. Brent*; Garey, James R.: Tardigrade Evolutionary Relationships

Tardigrades are a phylum of at least 750 species of small (0.1-0.5 mm) animals commonly known as water bears. They are allied with the arthropods and onychophorans within Panarthropoda. They live in marine, freshwater aquatic, and limno-terrestrial environments and feed mainly on the cytoplasmic fluid of plant cells although some are carnivorous. Many descriptions of tardigrade species exist, and the families, orders, and classes are well defined, but it is remarkable that there is currently no hypothesis of how the families, subfamilies, and genera of this entire phylum are related. The purpose of this project is to carry out a combined morphological and molecular based phylogenetic study of tardigrade evolutionary relationships using shared derived characters, 18S rRNA, cytochrome oxidase subunit I, and cytochrome b. The phylogeny will provide useful information in understanding how the various feeding mechanisms, habitat preferences and cryptobiosis evolved among the tardigrades and it is important because tardigrades are central to the understanding of protostome evolution.

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