Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Brownish, subrectangular mites with podonotalpodonotal:
  relating to the dorsal podosoma, the region of the idiosoma over the legs.
  , 2 mesonotal and pygidial shields
• Sternal shield divided, st1–2 and st3–4 on separate halves; genital shieldgenital shield:
  a shield or shields covering the genital opening; in female mongynaspine Mesostigmata this shield is usually called the epigynal (epigynial) shield.  
  with broad wings and a single pair of setae.
• Intercalary scleritesclerite:
  A component section of an exoskeleton; a plate forming the skeleton of an arthropod.
  of tarsustarsus:
  (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
  IV reduced to linear remnant; setae av4 and pv4 absent.
• Trochantertrochanter:
  the leg segment between the coxa and the femur.
  I of adult with 5 setae; femorafemur:
  (pl. femora) major leg segment between trochanter and genu; often subdivided into a basifemur and a telofemur.
  , genuagenu:
  (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
  and tibiaetibia:
  (pl. tibiae) the leg segment between the genu and the tarsus.
  I with 10 setae; tibiaetibia:
  (pl. tibiae) the leg segment between the genu and the tarsus.
  II–IV with 9 setae (2–1/1,2/1–2).
• Hypostomal setae in triangular array; palp apotelepalptarsal apotele:
  (= palp apotele, palptarsal claw) the most distal segment of the palp; absent in Acariformes, claw-like in Opilioacarida, and a subdistal, tined structure in the Mesostigmata.
  2-tined; movable digit of chelicerae without excrescences.
• Males with sternal-genital shieldgenital shield:
  a shield or shields covering the genital opening; in female mongynaspine Mesostigmata this shield is usually called the epigynal (epigynial) shield.  
  bearing 4 pairs of setae; genital opening between coxae III; fifth pair of sternal setaesternal setae:
  in Mesostigmata, the five pairs of setae in the intercoxal region designated st1-5; st1-3 are present in the larva and usually are borne on a sternal shield in the adult female; st4, the metasternal setae, are added in the deutonymph, often are borne on metasternal platelets, and sometimes on the sternal shield; st5, the genital setae, are added in the protonymph and usually borne on or are inserted laterad the epigynal shield in the adult female.
  on or near a separate plate between coxae IV.

Similar taxa

Microgynium has 4 setae on trochantertrochanter:
the leg segment between the coxa and the femur.
I, a single mesonotal shield, and has cheliceralcheliceral:
of or pertaining to the chelicera.
excrescences. Nothogynus have nude mesonotal scutellascutella:
(pl scutellae) small shields or platelets.
and pygidial shields, 4-segmented palps, and lack claws on tarsustarsus:
(pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
I. Polyaspidids have a nude genital shieldgenital shield:
a shield or shields covering the genital opening; in female mongynaspine Mesostigmata this shield is usually called the epigynal (epigynial) shield.  
. Saprosecans (Halolaelapidae) have posteriorposterior:
the back part of the body or towards that region in comparison, e.g., 'posterior to'.
opisthonotal horn-like processes.

Taxon not in this tool: Davacarids have 3 genital shields, short peritremes, a lobe-like process on the chelicerae, and setae av4/ pv4 on tarsitarsus:
(pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
IV. Sejids have setae av4/pv4.

Ecology and distribution

Microsejus truncicola Trägårdh is the only known species and is associated with tree stumps in boreal forests. The deutonymphdeutonymph:
(also deuteronymph) the second nymphal stage or instar.
is phoretic.

References

• Evans and Till 1979Evans and Till 1979:
  Evans EO and Till WM. 1979. Mesostigmatic mites of Britain and Ireland (Chelicerata: Acari-Parasitiformes): An introduction to their external morphology and classification. Transactions of the Zoological Society of London 35 (2): 145-270.
• Gilyarov and Bregatova 1977Gilyarov and Bregatova 1977:
  Gilyarov MS and Bregatova NG, eds. 1977. Handbook for the identification of soil-inhabiting mites, Mesostigmata. Zoological Institute of the Academy of Sciences, Petrograd.
• Johnston 1982bJohnston 1982b:
  Johnston DE. 1982b. Mesostigmata. pp. 112-116. In: Parker SP, ed. Synopsis and classification of living organisms, Vol. 2. McGraw-Hill, New York.
• Krantz 1961Krantz 1961:
  Krantz GW. 1961. A re-evaluation of the Microgynioidea, with a description of a new species of Microgynium (Acarina: Mesostigmata). Acarologia 3: 1-10.
• Walter and Krantz 1999Walter and Krantz 1999:
  Walter DE and Krantz GW. 1999. New early derivative mesostigmatans from Australia: Nothogynus, n. g., Nothogynidae, n. fam. (Mesostigmata: Microgyniina). International Journal of Acarology 25: 67-76.