Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Adults with holodorsal shieldholodorsal shield:
  a shield that covers all of the dorsum.  In Mesostigmata, the holodorsal shield is often interpreted as resulting from the fusion of podonotal and opisthonotal shields and a suture between these regions is often visible (see recurved and procurved).
  lacking seta J3
• Subcordate 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.
  with 13 setae (ZV1–2, JV1–3 + circumanals)
• Genital shieldgenital shield:
  a shield or shields covering the genital opening; in female mongynaspine Mesostigmata this shield is usually called the epigynal (epigynial) shield.  
  truncate posteriorly and bearing 1 pair of setae
• 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 and convex posteriorposterior:
  the back part of the body or towards that region in comparison, e.g., 'posterior to'.
  margin
• Metasternal setae on metasternal-endopodal shieldendopodal shield:
  (elements) narrow, strap-like, angular to subtriangular sclerites produced around the bases of the coxae in Mesostigmata; the anterior endopodal shields (I, II) are often fused to the sternal shield.
  that is fused anteriorly to sternal shieldsternal shield:
  a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
  
• Peritrematalperitrematal:
  (peritrematic) of or referring to the peritreme; adjectival form of peritreme.
  shield extending beyond coxae IV
• Arthrodial brusharthrodial brush:
  a brush like extension of the arthrodial membrane at the articulation of the movable and fixed digits in some Mesostigmata. Not to be confused with cheliceral excrescences that are produced from openings in the movable digit.
  vestigial
• 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 3-tines; tibiatibia:
  (pl. tibiae) the leg segment between the genu and the tarsus.
  I with 6 dorsaldorsal:
  relating to the upper or back side; opposed to ventral.
  setae; tibiatibia:
  (pl. tibiae) the leg segment between the genu and the tarsus.
  III with 8 dorsaldorsal:
  relating to the upper or back side; opposed to ventral.
  setae; tibiatibia:
  (pl. tibiae) the leg segment between the genu and the tarsus.
  IV with 8 dorsaldorsal:
  relating to the upper or back side; opposed to ventral.
  setae.

Similar taxa

Species of Pachyseius have spurs on tarsitarsus:
(pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
II and have st4 on a metasternal shield or in the soft cuticle. Species of Macrocheles have recurvedrecurved:
a curved suture or line of dehiscence that arches posteriorly; opposed to procurved.
peritremes. Ascid mites lack metasternal-endopodal shields. Some hypoaspidine Laelapidae have a metasternal-endopodal shield, but have anal, rather than ventrianal shields.

Simplified key to common genera of Pachylaelapidae

1. Females (and usually males) with spurspur:
   a projection, usually tooth- or spine-like, from the body or limbs.
   -like distaldistal:
   towards the free end of an appendage.
   setae on tarsustarsus:
   (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
   II.............................. 3
   - Spurspur:
   a projection, usually tooth- or spine-like, from the body or limbs.
   -like setae on tarsustarsus:
   (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
   II absent.............................. 2

2. Female with subcordate 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.
   with 13 setae (ZV1–2, JV1–3 + circumanals); genital shieldgenital shield:
   a shield or shields covering the genital opening; in female mongynaspine Mesostigmata this shield is usually called the epigynal (epigynial) shield.  
   truncate posteriorly and bearing 1 pair of setae; 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 and convex posteriorposterior:
   the back part of the body or towards that region in comparison, e.g., 'posterior to'.
   margin; metasternal setae on metasternal-endopodal shield; free-living or on dung beetles.............................. Zygoseius
   - Female with anal shield (rarely capturing 1–2 ventral setaeventral setae:
   in the Lindquist-Evans system used in the Mesostigmata, the ventral region has up to three longitudinal rows (Jv, Zv, Lv) with 1-5 transverse row designations.
   ); opisthogenital shield spreading laterally, with 2 pairs of setae and recurvedrecurved:
   a curved suture or line of dehiscence that arches posteriorly; opposed to procurved.
   posterior margin; associated with ants.............................. Sphaerolaelaps

3. Female sternal shieldsternal shield:
   a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
   bearing 4 pairs of setae, opisthogenital shield with 2 or more pairs of setae, and anal shield with 3 circumanal setaecircumanal setae:
   in Mesostigmata, the three setae (postanal and pair of peranal) setae surrounding the anal opening.
   .............................. 4
   - Female sternal shieldsternal shield:
   a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
   bearing 3 pairs of setae (st4 on small metasternal shield or in soft cuticle), 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 1 pair of seta, 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.
   with 7–10 setae.............................. Pachyseius

4. Tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   I with 5 dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   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.
   3-tined.............................. 5
   - Tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   I with 6 dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   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.
   2-tined.............................. 6

5. Genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   I with 5 dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   setae.............................. Onchodellus
   - Genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   I with 6 dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   setae.............................. Pachylaelaps

6. Seta st4 on small metasternal plate; dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield with 37 pairs of setae.............................. Pachyseiulus
   - Seta st4 on in soft cuticle; dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield with 35 pairs of setae.............................. Pseudopachyseiulus

References

Halliday 1997bHalliday 1997b:
Halliday RB. 1997b. Revision of the genus Zygoseius Berlese (Acarina: Pachylaelapidae). Acarologia 38: 3-20.