Acariformes

Prostigmata

Parasitengona

Erythraeina (Calyptostomatoidea, 1 family; Erythraeoidea, 2 families), Hydracarina (ca. 7 superfamilies and 50 families), Trombidiina (ca. 5 superfamilies and 12 families).

 

Diagnosis.  Medium to very large; soft-bodied to heavily sclerotised; primarily red or orange but can be any colour.  Terrestrial species often conspicuously hypertrichous, displaying a velvety red pelage.  Cheliceral bases separate; fixed digit of chelicera absent, movable digit hooked or linear.  Palps often raptorial with a well-developed clawlike seta on the tibia; development of the palp tarsus ranges from subterminal and thumblike, to terminal, to absent.  Gnathosoma retractile in some species.  Stigmata and peritremes, when present, between the cheliceral bases.  Terrestrial species usually with one or two pairs of prodorsal trichobothria, often mounted on a linear sclerotised plate (the crista metopica); eye lenses almost always well-developed.  Genital papillae usually present but variable in size and number.

 

Similar taxa.  Anystoidea

 

Ecology & Distribution.  The Parasitengona are united on the basis of their complex life cycle.  Larvae are parasites of invertebrates or vertebrates and are usually heteromorphic to the nymphal and adult stages.  The predatory deutonymphal stage takes place in between the inactive pupa-like proto- and tritonymphal stages.  Most postlarval Parasitengona are predators of small invertebrates, particularly arthropods, but a few species are parasitic as adults.  The majority of the described species belong to the Hydracarina, or ‘water mites’.  Only in rare circumstances are water mites likely to be collected in soil samples, although some species do venture into damp moss, while others inhabit wet treeholes.  Water mites can be keyed to subfamily using Proctor et al. (1998) or to genus using Harvey (1998).  The approximately 2000 named species of terrestrial Parasitengona fall into two groups: the Erythraeina, which have chelicerae that can be retracted within the idiosoma; and the Trombidiina, which have non-retractable chelicerae.  Members of both groups are often large (5-8 mm), bright red and furry, resulting in the common name ‘velvet mites’.  They are abundant and diverse inhabitants of leaf litter, moss, the upper layers of soil, and foliage.  Bush-walkers in Australia are familiar with the larvae of the trombidiine families Leeuwenhoekiidae and Trombiculidae as ‘scrub itch mites’, while those of North America know them as ‘chiggers’.  The bites of these mite larvae usually cause annoying itching, and in some cases result in the transfer of scrub typhus (= tsutsugamushi) agents.  Thanks to the prolific works of R.V. Southcott, the terrestrial Parasitengona of Australia are relatively well-described; however, familial diagnoses are vague.  Thus in this compilation we provide a key only to the subcohort level.

 

References

Harvey, M. S. 1998. The Australian Water Mites. A Guide to the Families and Genera.  CSIRO Publishing, Melbourne.

Kethley JB.  1982.  Acariformes.  In: Parker, S.P. (ed.)  Synopsis and Classification of Living Organisms.  McGraw-Hill, New York, pp. 126-136.

Kethley JB.  1990.  Acarina: Prostigmata (Actinedida).  In DL Dindal (ed.)  Soil Biology Guide.  John Wiley & Sons, New York, pp. 667-756.

Krantz GW.  1978.  A Manual of Acarology.  OSU Bookstores: Corvallis.

Proctor, HC et al. 1998.  Key to subfamilies and families of water mites (Hydracarina) in Australia.  Interactive Guide to Australian Aquatic Invertebrates, CSIRO, Canberra.

Southcott RV. 1961. Studies on the systematics and biology of the Erythraeoidea (Acarina), with a critical revision of the genera and subfamilies.  Aust. J. Zool. 9: 367-610.

Southcott RV. 1986. Studies on the taxonomy and biology of the subfamily Trombidiinae (Acarina : Trombidiidae) with a critical revision of the genera.  Aust. J. Zool. Supplementary Series 123: 1-116.

Southcott RV. 1987. The classification of the mite families Trombellidae and Johnstonianidae and related groups, with the description of a new larva (Acarina : Trombellidae : Nothotrombidium) from North America. Trans. Roy. Soc. S. Aust. 111: 25-42.

Walter DE & Proctor HC.  1999.  Mites: Ecology, Evolution and Behaviour.  University of NSW Press, Sydney and CABI, Wallingford.

Welbourn WC. 1991. Phylogenetic studies of the terrestrial Parasitengona.  In: F. Dusbabek and V. Bukva (eds.) Modern Acarology, Vol. 2. Academia, Prague,and SPB Academic Publishing, The Hague, pp. 163-170.