This investigation was carried out primarily to study the semi-aquatic tardigrade fauna of Southwestern Virginia. Specimens were obtained from mosses and lichens and were mounted by use of a procedure employing a modification of Hoyer's medium. During the course of this study, 694 specimens were obtained and the following species were identified: Batillipes friaufi sp. n., Echiniscus (Hypechiniscus) gladiator, Echiniscus (Echiniscus) virginicus sp. n., Pseudechiniscus suillus, Macrobiotus macronyx, Macrobiotus intermedius,Macrobiotus richtersi, Macrobiotus harmsworthi, Macrobiotus hufelandi, Macrobiotus echinogenitus, Hypsibius (Isohypsibius) tuberculatus, Hypsibius (Isohypsibius) nodosus, Hypsibius (Isohypsibius) prosostomus, Hypsibius (Isohypsibius) tetradactyloides, Hypsibius (Isohypsibius) canadensis, Hypsibius (Hypsibius) convergens, Hypsibius (Hypsibius) conjungens, Hypsibius (hypsibius) oberhaeuseri, Diphascon bullatus, Diphascon angustatus, Diphascon sconticus, Diphascon belgicae, Diphascon ninguis, Diphascon nodulosus, Itaguascon bellinae and Milnesium tardigradum. Collection data, discussion of the taxonomic status and previous morphological observations were presented for each species. Recommendations were made concerning the discarding of egg morphology as a valid basis for species description and identification. The practice of using numbers for taxonomic entities in tardigrade systematics was observed to be deplorable and the abandonment of such usages was urged. Evidences for the consideration of the Tardigrada as a phylum were presented and a taxonomic hierarchy was erected for this disposition. To complete this taxonomic scheme, the Heterotardigrada and Eutardigrada were accorded class status, the Arthrotardigrada and Echiniscida (= Echiniscoidea) were raised to ordinal rank and a new order, Diplotardigrada, was included with the Eutardigrada. The following new family names, made mandatory by the rules of nomenclature, were presenteda Batillipidae (= Discopodidae), Tetrakentronidae (= Onychopodidae), Echiniscoididae (= Nudechiniscidae), Echiniscidae (= Scutechiniscidae) and Milnesiidae (= Arctiscidae). The previously suggested phylogenetic schemes for the tardigrades were reviewed and the evidences for affinities of the Tardigrada were presented. A bibliography of the recent literature on the tardigrades was compiled. / Doctor of Philosophy