Slowly The Animal Bar Code And The Seven Kinds Of Tardigrade Phylogeny Study

Tardigrades are hydrophytic, micrometazoan invertebrate. Tardigrades are generally considered an independent phylum. Recent phylogenetic studies based on 18SrRNA show that Tardigrades and Arthropoda are sister group. The body length of Tardigrades ranges from 250 to 500μm. They show a bilateral symmetry with four pairs of legs, each leg is ended with claw. They possess complete nervous, digestive system and the reproductive system. They lack respiratory and circulatory system. Most tardigrades are terrestrial species. They live among moist mosses, lichens, soil, leaf litters and cushion-shaped flowering plants. Tardigrades can survive extreme conditions. They are famous for unique cryptobiotic stasis phenomenon. Tardigrades can enter cryobiosis, anhydrobiosis, asmobiosis and anoxybiosis, when they are exposed to low temperature, high pressure, dehydration, and anoxic environment. The taxonomic identification of tardigrades is based on the epidermis, the legs, claw, mouthparts complex absorption, pharynx, head appendages, the reproductive structure and eggs.The DNA barcoding technology uses a standard purpose gene as a tool to analyze and identify species. We usually use the rRNA 16S.18S rRNA, rRNA 12S and CO I gene in the present work of DNA barcoding. Compared with rRNA genes, CO I gene has a lot of advantages:it is conservative and have certain mutation, the length of the gene sequence is appropriate for the amplification by general primer. The mtCoI gene was selected as the molecular marker to reconstruct the phylogenetic relationship among the tardigrade species used in this study.The DNA barcoding of four species of tardigrades was studied. A total of 30 Co I gene sequences of seven species, including six sequences downloaded from GenBank data base, were used to build phylogenetic tree using Neighbor Joining (NJ), Maximum Likelihood (ML) and MrBayes (BI) methods. The results from the phylogenetic analysis at the molecular level are consistent with the results based on morphology.