Acari in water

Acari or Acarina are a taxon of arachnids (ie a sequence with two super-order, and Acariformes Parasitiformes, a subclass).
They are generally small in size: some are microscopic, measuring only a few tens of microns, the largest not exceeding 2 cm (except engorged ticks that in tropical-equatorial species can grow as big as a "beautiful "cherry).