What is "hydrachnidiae"

Hydrachnidiae also known as "water mites", Hydracarina or Hydrachnellae, are a group of mites covering more than 40 families and 5 000 species (Smith & Cook 1991) found in freshwater and marine habitats. As water mites of Africa, Asia, and South America have not been well-studied, the numbers are likely to be far greater. Other taxa of parasitengone mites include species with semi-aquatic habits, but only the Hydracarina are properly subaquatic. They exist in a variety of freshwater bodies, such as treeholes, hot springs, deep lakes and waterfalls, and some have adapted to marine environments.