Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Arctoseiinae with shallowly incised dorsaldorsal:
  relating to the upper or back side; opposed to ventral.
  shield, holotrichous, with z3, J2, S1
• 10–11 pairs of marginal r–R 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.
  on soft cuticle laterally, none on dorsaldorsal:
  relating to the upper or back side; opposed to ventral.
  shield
• Genugenu:
  (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
  and tibiatibia:
  (pl. tibiae) the leg segment between the genu and the tarsus.
  I each with 13 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.
  (av2 present)
• Genugenu:
  (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
  III with 8–9 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.
  , tibiatibia:
  (pl. tibiae) the leg segment between the genu and the tarsus.
  III with 8 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 absent on both)
• Genugenu:
  (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
  IV with 8–9 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.
  (pv1 absent)
• 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 usually on presternal plateletspresternal platelets:
  small sclerotized plates anterior to the sternal shield and laterad or posteriad the base of the tritosternum in some Mesostigmata.
  
• Usually found in coastal habitats

Similar taxa

Similar taxa not in Lucid key (see below) Arctopsis Athias-Henriot. Also see key to small Rhodacarus-like mites.

Similar taxa in key. Iphidozercon Berlese, Neojordensia Athias-Henriot, Xenoseius Lindquist and Evans, Zerconopsis Hull, Arctoseoides Willmann, Leioseius Berlese

Key to genera of Arctoseiinae and similar Ascinae

1. Leg chaetotaxychaetotaxy:
   the use of setal position and form in taxonomy; see Lindquist-Evans system, Grandjean system, Rostral-lamellar system, etc.
   reduced, maximum setation: genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   II = 10, genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   IV = 7, tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   III = 7, tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   IV = 7; opisthonotalopisthonotal:
   dorsal opisthosoma.
   region of dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield usually with 4 pairs of lateral setae (S1 present, S2 usually absent); deutosternal denticular rows moderately wide, multidenticulate.............................. 2
   - Leg chaetotaxychaetotaxy:
   the use of setal position and form in taxonomy; see Lindquist-Evans system, Grandjean system, Rostral-lamellar system, etc.
   without above reductions, minimum setation: genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   II = 11, genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   IV = 9, tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   III = 8, tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   IV = 10; opisthonotalopisthonotal:
   dorsal opisthosoma.
   region of dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield usually with 5 pairs of lateral setae (S2 present, S1 rarely absent); deutosternal denticular rows narrow, each with few (usually 2–6) denticlesdenticles:
   small tooth-like processes, e.g., on the subcapitula of ticks and many mesostigmatans.
   .............................. 5

2. Tarsitarsus:
   (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
   II–IV each with dorso-proximalproximal:
   towards the base of a structure; on a limb, towards the insertion on the body; sometimes also = approximate.
   setae ad2, pd2 elongate, curved; genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   III usually with 8 setae; female with 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.
   bearing 1–6 pairs of 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.
   in addition to circumanal setaecircumanal setae:
   in Mesostigmata, the three setae (postanal and pair of peranal) setae surrounding the anal opening.
   .............................. 3
   - Tarsitarsus:
   (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
   II-IV with dorso-proximalproximal:
   towards the base of a structure; on a limb, towards the insertion on the body; sometimes also = approximate.
   setae not elongate or curved; genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   III with 7 setae (pv1 absent); female with anal shield bearing only circum-anal setae (rarely with 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.
   JV3 on shield).............................. 4

3. Tarsustarsus:
   (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
   I without claws; dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield setae j1 & z1 smooth, short and blunt or barbed and variable in length; other dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield setae simplesimple:
   unadorned; simple setae are needle-like and without hairs or pectins.
   (J5 sometimes barbed), none paddle-shaped.............................. Xenoseius
   - Tarsustarsus:
   (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
   I with claws; dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield setae j1 and z1 smooth, pointed (j1 rarely paddle-shaped), variable in length; some dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield setae (always s4 and Z5) paddle-shaped.............................. Zerconopsis

4. Vertexvertex:
   an anterior extension of the idiosoma that covers the capitulum in many uropodid mites.
   of dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield strongly arched downward, setae j1 concealed from above; peritremes sharply recurvedrecurved:
   a curved suture or line of dehiscence that arches posteriorly; opposed to procurved.
   distally; dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield without midlateral incisions; tarsitarsus:
   (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
   II–IV with 1 (al1) or 2 (al1, pl1) dorso-lateral subapical setae very slender and elongate; palp tarsustarsus:
   (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
   with macroseta.............................. Iphidozercon
   - Vertexvertex:
   an anterior extension of the idiosoma that covers the capitulum in many uropodid mites.
   of dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield not strongly arched downward, setae j1 visible from above; anterior extremities of peritremes not recurvedrecurved:
   a curved suture or line of dehiscence that arches posteriorly; opposed to procurved.
   ; dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield with or without midlateral incisions; tarsitarsus:
   (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
   II-IV with neither of dorso-lateral subapical setae slender and elongate; palp tarsustarsus:
   (pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
   without macroseta.............................. Arctoseius

5. Dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield lacking setae z1; epistomegnathotectum:
   (= 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.
   convex and smooth or slightly denticulatedenticulate:
   bearing small, sharp processes, e.g., the hypostome of ticks.
   ; genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   I with 12 setae (av2 absent), tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   II with 9 setae (ad2 absent).............................. 6
   - Setae z1 present; 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.
   bi- or triramous; genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   I with 13 setae, tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   II with 10 setae.............................. 7

6. Dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield with midlateral incisions; all r–R marginal setae on soft cuticle flanking dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield; female with: first 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 sternal shieldsternal shield:
   a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
   , genital setae and pores on soft cuticle flanking epigynialepigynal:
   (also epigynial) of or relating to the female genital opening or a shield protecting it.
   shield, anal shield bearing only circum-anal setae.............................. Arctopsis
   - Dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield lacking midlateral incisions; r–R marginal setae on edges of dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield; female with: first 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 jugular plates separated from sternal shieldsternal shield:
   a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
   or on margin of shield, genital setae and pores on epigynialepigynal:
   (also epigynial) of or relating to the female genital opening or a shield protecting it.
   shield, ventri-anal shield incorporating metapodal platesmetapodal shields:
   (also metapodal plates, metapodal platelets, metapodal sclerites) in Mesostigmata, a pair (sometimes fused) of small sclerites posteriad coxae IV in the ventral region that probably reflect muscle attachments.
   and bearing 4–5 pairs of setae in addition to circum-anal setae.............................. Neojordensia

7. Dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield lacking setae z3, J2, S1; R3, R4 on dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield, others (r6, R2, R5) absent; genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   and tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   I each with 12 setae (av2 absent); genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   III with 10 setae, tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   III with 9 setae (pl2 present on both); genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   IV with 10 setae (pv1 present).............................. Arctoseoides
   - Dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield holotrichous, with z3, J2, S1; 10–11 pairs of marginal r–R setae on soft cuticle laterally, none on dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   shield; genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   and tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   I each with 13 setae (av2 present); genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   III with 8–9 setae, tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   III with 8 setae (pl2 absent on both); genugenu:
   (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
   IV with 8–9 setae (pv1 absent).............................. Leioseius

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.
• Lindquist and Evans 1965Lindquist and Evans 1965:
  Lindquist EE and Evans GO. 1965. Taxonomic concepts in the Ascidae, with a modified setal nomenclature for the idiosoma of the Gamasina (Acarina: Mesostigmata). Memoirs of the Entomological Society of Canada 47: 1-64