Acarids are mites belonging to the suborder Astigmata in the Order Acariformes. Most species are terrestrial, among them serious stored-product pests such as Acarus siro. In general, acarids appear to be detritivorous or fungivorous. A number of genera are aquatic or semi-aquatic, and inhabit a wide range of habitats including treeholes and bromeliads (Fashing 1994; OConnor 1994), and slow-flowing streams (pers. obs., HCP). They also have been found on fish and leeches, where they may feed on dead skin or fungus (Proctor et al. 1997).
Aquatic astigmatans of the families Acaridae, Algophagidae and Hyadesiidae are similar in appearance. However, acarids have tarsal claws that attach directly to the tarsi, whereas algophagids and hyadesiids have tarsal claws at the ends of flattened pulvilliform pretarsal stalks. In algophagids, the pretarsi of all legs are the same length, while in hyadesiids the pretarsi of legs I and II are much longer.
Fashing, N.J. 1994. Life-history patterns of astigmatid inhabitants of water-filled treeholes. pp. 160-185 in M.A. Houck (ed.) Mites: ecological and evolutionary studies of life-history patterns. Chapman & Hall, New York.
Krantz, G.W. 1978. A Manual of Acarology. 2nd edition. Oregon State University Book Stores, Corvallis, Oregon.
OConnor, B.M. 1994. Life-history modifications in astigmatid mites. pp. 136-159 in M.A. Houck (ed.) Mites: ecological and evolutionary studies of life-history patterns. Chapman & Hall, New York.
Proctor, H.C., H.M. Gray and B.M. OConnor. 1997. Subaquatic mites (Acari: Astigmata) associated with adult freshwater leeches (Hirudinea: Erpobdellidae). J. Nat. Hist. (Lond.) 31: 539-544.
Walter, D.E. and H.C. Proctor. 1999. Mites: Ecology, Evolution and Behaviour. University of New South Wales Press, Sydney, New South Wales.