Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Opisthonotalopisthonotal:
  dorsal opisthosoma.
  region of dorsaldorsal:
  relating to the upper or back side; opposed to ventral.
  shield with 12–15 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.
  , including J1–5
• Female with sternal 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.
  st1 and st3 subequal in length
• Metasternal plates and 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.
  
• Male with metasternal 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.
  ; median lobes of pulvilluspulvillus:
  a membranous, pad-like structure associated with the claws in Mesostigmata. 
  of legs II–IV acute
• Genugenu:
  (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
  II with 10 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.
  (pl2 present)
• Legs II–IV with median lobe of pulvilluspulvillus:
  a membranous, pad-like structure associated with the claws in Mesostigmata. 
  slender, acute or narrowly rounded
• Para-anal 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.
  inserted level with or posteriorposterior:
  the back part of the body or towards that region in comparison, e.g., 'posterior to'.
  to hind margin of anus, and usually longer than post-anal setaanal seta:
  any seta on an anal valve or ascribed to the anal region; pseudanal setae ps1–3 in spider mites; true anal setae may be present in acariform mites that add segment AN
  
• Femorafemur:
  (pl. femora) major leg segment between trochanter and genu; often subdivided into a basifemur and a telofemur.
  I and II with 11 and 10 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.
  respectively (each lacking v–3)
• Anterioranterior:
  the front part of the body or towards that region in comparison, e.g., 'anterior to'
  rostral and internal 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.
  trochanter 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.
  extremely long, whip-likewhip-like:
  long, slender and sinuous as in the posterior setae of some phytoseiid mites (Mesostigmata) or the stylets of spider mites and their relatives (Prostigmata: Tetranychoidea).
  , taperingtapering:
  drawn out or with margins converging.
  only near tip
• Phytoseiid-type sperm access systemsperm access system:
  a term used for a complex secondary insemination system in in female mites; implies more than simple sperm storage is occurring.    In the dermanyssine Mesostigmata, two basic types of sperm access systems are known - the laelapid type and the phytoseiid type.
  
• Fixed cheliceralcheliceral:
  of or pertaining to the chelicera.
  digit with a deep receptacle that receives the tip of the movable digit
• Often with a long post-stigmatic arm of the peritremeperitreme:
  a groove or gutter on the surface connecting to a stigmatal opening.  In Mesostigmata the peritremes are lateral and run above the coxae of the legs and usually run to near the anterior margin of the idiosoma, but they may be very short or vestigial.  In Prostigmata peritremes are usually found on the anterior margin of the idiosoma, as short processes to either side of the capitulum (emergent peritremes), or as simple to complex lines or reticulations of short, connected chambers on the dorsal surface of the chelicerae or stylophore.
  extending along coxacoxa:
  the basal segment of the leg, articulating with (Parasitiformes) or fused to (Acariformes) the body wall.
  IV
• Male with or without metasternal 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.
  

Similar taxa

Key to females of genera of Platyseiinae

1. Opisthonotalopisthonotal:
   dorsal opisthosoma.
   region of dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield markedly hypotrichous, with only 5 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.
   (Z1, Z4, Z5, S4, J5); sternal 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.
   st4 in soft cuticle; with anal shieldanal shield:
   in Mesostigmata, a ventral shield bearing the anal opening and circumanal setae (po, pa), but without any ventral setae or pores (lyrifissures) [see ventrianal shield]
   ; median lobes of pulvilluspulvillus:
   a membranous, pad-like structure associated with the claws in Mesostigmata. 
   of legs II–IV blunt.............................. Cheiroseiulus
   - Opisthonotalopisthonotal:
   dorsal opisthosoma.
   region of dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield with 12–15 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.
   ; with metasternal plates bearing st4 and 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.
   ; median lobes of pulvilluspulvillus:
   a membranous, pad-like structure associated with the claws in Mesostigmata. 
   of legs II–IV acute.............................. 2

2. Opisthonotalopisthonotal:
   dorsal opisthosoma.
   region of dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield with 2–4 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.
   in J-series; first pair of sternal 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.
   (st1) distinctly shorter than third pair (st3); distance between fifth and sixth rows of deutosternal denticlesdeutosternal denticles:
   rows of small teeth-like projections (often irregular and sometimes reduced to a single tooth) running transversely across the deutosternal groove and sometimes onto the lateral faces of the subcapitulum.
   nearly twice that between fourth and fifth rows; tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   II with 9 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.
   (pd1 absent)............................. Platyseius
   - Opisthonotalopisthonotal:
   dorsal opisthosoma.
   region of dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield with 5 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.
   in J-series; 1st and 3rd pairs of sternal 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.
   subequal in length; distance between 5th and 6th rows of deutosternal denticlesdeutosternal denticles:
   rows of small teeth-like projections (often irregular and sometimes reduced to a single tooth) running transversely across the deutosternal groove and sometimes onto the lateral faces of the subcapitulum.
   similar to that between 4th and 5th rows; tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   II with 10 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.
   (pd1 present).............................. Cheiroseius

Ecology and distribution

Mites of the genus Cheiroseius feed on nematodes in moist soils, and are abundant in wet forest litter, especially along lake and stream margins; these mites often have extensive peritrematalperitrematal:
(peritrematic) of or referring to the peritreme; adjectival form of peritreme.
surfaces that appear to act as plastrons. Others are found in treeholes, decaying logs, and on bracket fungi. About 65 species have been described and many more remain to be described. Many species appear to be subaquatic and able to tolerate flooding. Often the peritremeperitreme:
a groove or gutter on the surface connecting to a stigmatal opening.  In Mesostigmata the peritremes are lateral and run above the coxae of the legs and usually run to near the anterior margin of the idiosoma, but they may be very short or vestigial.  In Prostigmata peritremes are usually found on the anterior margin of the idiosoma, as short processes to either side of the capitulum (emergent peritremes), or as simple to complex lines or reticulations of short, connected chambers on the dorsal surface of the chelicerae or stylophore.
is plastron-likeplastron-like:
peritremes that are flattened and broad and serve as an incompressible plastron in mesostigmatans living in wet habitats.  
. Some adult female Cheiroseius are phoretic on tipulid flies and others have been found associated with.

References

• Evans and Hyatt 1960Evans and Hyatt 1960:
  Evans GO, Hyatt KH. 1960. A revision of the Platyseiinae (Mesostigmata: Aceosejidae) based on material in the collections of the British Museum (Natural History). Bulletin of the British Museum (Natural History) Zoology 6 (2): 27–101.
• Evans and Till 1979Evans and Till 1979:
  Evans EO, 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.
• Halliday et al. 1998Halliday et al. 1998:
  Halliday RB, Walter DE, Lindquist EE. 1998. Revision of the Australian Ascidae (Acarina: Mesostigmata). Invertebrate Taxonomy 12: 1–54.
• Karg 1993Karg 1993:
  Karg W. 1993. Acari (Acarina), Milben Parasitiformes (Anactinochaeta) Cohors Gamasina Leach, Raubmilben. Die Tierwelt Deutschlands 59: 1–523.
• Kitching and Callaghan 1982Kitching and Callaghan 1982:
  Kitching RL, Callaghan C. 1982. The fauna of water-filled tree holes in box forest in south-east Queensland. Australian Entomological Magazine 8: 61–70.
• Krantz 1962Krantz 1962:
  Krantz GW. 1962. Acari. Free-living Mesostigmata. II. The family Aceosejidae. Parc National de la Garamba - Mission H. de Saeger 34: 3–29.
• Krantz 1986Krantz 1986:
  Krantz GW. 1986. A manual of acarology [2nd ed., emended 1986]. Oregon State University Book Stores, Corvallis.
• Krantz and Ainscough 1990Krantz and Ainscough 1990:
  Krantz GW, Ainscough B. 1990. Mesostigmata. pp. 583–665. In: Dindal DL, ed. Soil biology guide. John Wiley & Sons, Brisbane.
• Lindquist 2003Lindquist 2003:
  Lindquist EE. 2003. Observations on mites of the subfamily Platyseiinae, with descriptions of two new species of Platyseius from North America (Acari: Mesostigmata: Ascidae). pp. 155–182. In: Smith IM, ed. An acarological tribute to David R. Cook. Indira Publishing House, West Bloomfield.