Acarina (also Acari) is a group of arachnids consisting of ticks and mites. Its classification as an order, superorder, or subclass is being debated on due to the diversity of the taxon though at present it is usually granted a superorder rank. Relationships of acarina organisms to other arachnids are not clear.
Majority of acarines appear as minute to small arachnids with sizes 0.08–1.00 millimeter or 0.0031–0.039 inch. The bigger members of the taxon grow from 10 to 20 millimeters or 0.39 to 0.79 inch. As of 1999, more than 50,000 Acarina species have been described.
Acarines exist in almost every habitat from terrestrial to freshwater and saltwater. Several acarine species are parasitic having vertebrates and invertebrates alike as their hosts. There are also those that predate smaller arthropods and others that are classified as detritivores, helping break down decaying or dead organic matter. Plant-feeding acarines have the potential to damage crops.