Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Adults with 2 dorsaldorsal:
  relating to the upper or back side; opposed to ventral.
  shields, each with serrateserrate:
  with closely set teeth that resemble the cutting edge of a saw.
  to crenulate margins with interspersed marginal setaeseta:
  (pl. setae, from L. = bristle) cuticular process composed of a hollow shaft (sometimes filled with a refractive material) produced from a membranous socket (the alveolus); the hair-like, spine-like, branched or variously expanded structures on the surfaces of the legs and body.  Most setae function as mechanoreceptors, but others (e.g., solenidia) are chemoreceptors or have unknown or ambiguous functions.
  and usually with 4 deep semi-circular depressions (fossaefossa:
  (pl. fossae) a pit or recessed area in the integument (also see pedofossa).
  ) on the posteriorposterior:
  the back part of the body or towards that region in comparison, e.g., 'posterior to'.
  shield
• Peritrematalperitrematal:
  (peritrematic) of or referring to the peritreme; adjectival form of peritreme.
  shields broad, bearing 1–3 pairs of setaeseta:
  (pl. setae, from L. = bristle) cuticular process composed of a hollow shaft (sometimes filled with a refractive material) produced from a membranous socket (the alveolus); the hair-like, spine-like, branched or variously expanded structures on the surfaces of the legs and body.  Most setae function as mechanoreceptors, but others (e.g., solenidia) are chemoreceptors or have unknown or ambiguous functions.
  
• Peritremes typically short in adults, often comma-shaped
• Euanal setaeseta:
  (pl. setae, from L. = bristle) cuticular process composed of a hollow shaft (sometimes filled with a refractive material) produced from a membranous socket (the alveolus); the hair-like, spine-like, branched or variously expanded structures on the surfaces of the legs and body.  Most setae function as mechanoreceptors, but others (e.g., solenidia) are chemoreceptors or have unknown or ambiguous functions.
  may be present

Diagnosis

Brown, yellow or pinkish, oval to subrectangular mites with separate podonotalpodonotal:
relating to the dorsal podosoma, the region of the idiosoma over the legs.
and opisthosomalopisthosomal:
(opisthosomatic) adjectival form of opisthosoma.
shields usually bearing r-R series and often with serrateserrate:
with closely set teeth that resemble the cutting edge of a saw.
margins; often somewhat hypertrichous; podonotal shieldpodonotal shield:
the anterior shield in mesostigmatans with divided dorsal shields.  
usually with 4 deep depressions near its posteriorposterior:
the back part of the body or towards that region in comparison, e.g., 'posterior to'.
margin at the insertion of major dorso-ventralventral:
relating to the lower or under side; opposed to dorsal.
muscles, and bearing ventralventral:
relating to the lower or under side; opposed to dorsal.
seta JV5. Female sternal shieldsternal shield:
a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
with 3 pairs of setae (st1–3) and 2 pairs of lyrifissures (stp1–2); st4 and stp3 usually on small metasternal platelets; epigynialepigynal:
(also epigynial) of or relating to the female genital opening or a shield protecting it.
shield axe-shape, with 1 pair of setae; inguinal glands on small platelets between basebase:
the usually columnar basal part of the tritosternum; sometimes expanded and rectangular or otherwise modified; the most basal part of any structure.
of epigynialepigynal:
(also epigynial) of or relating to the female genital opening or a shield protecting it.
shield and coxae IV or in soft cuticle; anal opening with 2 valves (often with a pair of euanal setaeeuanal setae:
setae borne on the anal valve (Parasitiformes).
) in large ventrianal shieldventrianal shield:
in Mesostigmata, a ventral shield bearing the anal opening, circum anal setae, and one or more pairs of ventral setae or pores (lyrifissures) [see anal shield]; maybe rather narrow or very broad and covering most of the gaster.
, free from truncate peritrematalperitrematal:
(peritrematic) of or referring to the peritreme; adjectival form of peritreme.
shield or fused to peritrematalperitrematal:
(peritrematic) of or referring to the peritreme; adjectival form of peritreme.
-metapodal shields. Peritremes usually short in adults (less than anterior margin of coxacoxa:
the basal segment of the leg, articulating with (Parasitiformes) or fused to (Acariformes) the body wall.
II), but longer in deutonymphs, on broad shields bearing 1–3 pairs of setae. Tarsustarsus:
(pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
I with claws. Palppalp:
(= pedipalp) the second pair of limbs in arachnids, used in feeding and originating on either side of the chelicerae.  In mites, the palps may be vestigial, with only a few segments, or have a maximum of  5 freely articulating segments (rarely the femur is subdivided) and a distal or subdistal apotele.
genu with 6 setae; 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.
with 2 tines. Tectumgnathotectum:
(= epistome, tectum) an often membranous dorsal projection of the anterior margin of the basis capitulum in Mesostigmata; often diagnostic at family-, genus- or species-levels; also often difficult to see without high magnification and good optics.
denticulate to spinose; subcapitular gutter often with pencil-like rows of ridges; corniculicorniculus:
(pl. corniculi) (also, external malae) a usually horn-like process (sometimes toothed, bifurcate, trifurcate, spine-like, spatulate, or membranous) on the subcapitulum of parasitiform mites that usually supports the salivary styli.  A toothed corniculus could be confused with a rutellum, a possibly homologous structure in Acariformes and Opilioacarida. Phytoseiid image is spatulate corniculus.
horn-like; hypostomal setae in triangular array; hypostomal groove broad, with denticlesdenticles:
small tooth-like processes, e.g., on the subcapitula of ticks and many mesostigmatans.
. Chelicerae chelate-dentatechelate-dentate:
pincer-like chelicerae with teeth.
; pilus dentilispilus dentilis:
(pl. pili dentilis) a seta-like or membranous sensory organ inserted ventrolaterally on the fixed digit of the chelicera of many Mesostigmata.
setiform. Male genital opening on intercoxal shield, valve with a pair of setae; neither chelicerae nor legs obviously modified for sperm transfer.

Similar taxa

Heatherellidae have elaborate setae on the margins of the their shields, but also have large, spout-like gland openings and subdivided opisthonotal shielding. Some ascids (Ascinae) may seem superficially similar to zerconids, but lack deep pits and serrate margins on the dorsal shield, as well as having a reduced chaetotaxy, seta JV5 fully ventral, and a dermanyssine reproductive system. Adult female Coprozercon (Coprozerconidae) lack a opisthonotal shield.

References

• Blaszak 1974Blaszak 1974:
  Blazak C. 1974. Zerconidae (Acari, Mesostigmata) Polski. Monografie Fauny Polski. 3: 315 pp.
• Blaszak et al. 1995Blaszak et al. 1995:
  Blazak C, Cokendolpher JC, Polyak VJ. 1995. Paleozercon cavernicolous, n. gen., n. sp., fossil mite from a cave in the southwestern USA (Acari, Gamasida: Zerconidae), with a key to Nearctic genera of Zerconidae. International Journal of Acarology 21: 253–259.
• 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.
• Halaskova 1969Halaskova 1969:
  Halaskova V. 1969. Zerconidae of Czechoslovakia (Acari: Mesostigmata). Acta Universitatis Carolinae, Biologica 3-4: 175-352.
• 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 1978Krantz 1978:
  Krantz GW. 1978. A manual of acarology [2nd ed.]. Oregon State University Book Stores, Corvallis.
• Krantz and Ainscough 1990Krantz and Ainscough 1990:
  Krantz GW and Ainscough B. 1990. Mesostigmata. pp. 583-665. In: Dindal DL, ed. Soil biology guide. John Wiley & Sons, Brisbane.
• Moraza and Lindquist 1998Moraza and Lindquist 1998:
  Moraza ML and Lindquist EE. 1998. Coprozerconidae, a new family of zerconoid mites from North America. Acarologia 39 (4): 292-313.
• Walter 1988bWalter 1988b:
  Walter DE. 1988b. Nematophagy by soil arthropods from the shortgrass steppe, Chihuahuan desert, and Rocky Mountains of the central United States. Agriculture, Ecosystems & Environment 24: 307-316.