[Kingdom] Animalia Linnaeus, 1758 - animals Grade Enterozoa Grade Cœlomata Phylum Appendiculata {Lankester} Branch Gnathopoda Straus-Durkheim, 1829 Grade Condylopoda Class Arachnida Lamarck, 1801 Branch Tracheopulmonata Order Acarina Baraud, 1965 see Order Acari Leach, 1817 Genus Hydrachna Müller, 1776