Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Arctoseiinae with tarsus I without claws
• Dorsal shield setae j1 and z1 smooth, short and blunt or barbed and variable in length; other dorsal shield setae simple (J5 sometimes barbed), none paddle-shaped; S2 present
• Tarsi II–IV each with dorso-proximal setae ad2, pd2 elongate, curved; genu III usually with 8 setae
• Female with ventrianal shield bearing 1–6 pairs of ventral setae in addition to circumanal setae

Similar taxa

Similar taxa not in Lucid key (see below). Arctoseoides Willmann, Zercoseius Berlese, Arctopsis Athias-Henriot, Leioseius Berlese

Similar taxa in key. Arctoseius Thor, Iphidozercon Berlese, Neojordensia Athias-Henriot, Zerconopsis Hull

Key to Genera of Arctoseiinae and similar Ascinae

1. Leg chaetotaxy reduced, maximum setation: genu II = 10, genu IV = 7, tibia III = 7, tibia IV = 7; opisthonotal region of dorsal shield usually with 4 pairs of lateral setae (S1 present, S2 usually absent); deutosternal denticular rows moderately wide, multidenticulate.............................. 2
   - Leg chaetotaxy without above reductions, minimum setation: genu II = 11, genu IV = 9, tibia III = 8, tibia IV = 10; opisthonotal region of dorsal shield usually with 5 pairs of lateral setae (S2 present, S1 rarely absent); deutosternal denticular rows narrow, each with few (usually 2–6) denticles.............................. 5

2. Tarsi II–IV each with dorso-proximal setae ad2, pd2 elongate, curved; genu III usually with 8 setae; female with ventrianal shield bearing 1–6 pairs of ventral setae in addition to circumanal setae.............................. 3
   - Tarsi II-IV with dorso-proximal setae not elongate or curved; genu III with 7 setae (pv1 absent); female with anal shield bearing only circum-anal setae (rarely with ventral setae JV3 on shield).............................. 4

3. Tarsus I without claws; dorsal shield setae j1 & z1 smooth, short and blunt or barbed and variable in length; other dorsal shield setae simple (J5 sometimes barbed), none paddle-shaped.............................. Xenoseius
   - Tarsus I with claws; dorsal shield setae j1 and z1 smooth, pointed (j1 rarely paddle-shaped), variable in length; some dorsal shield setae (always s4 and Z5) paddle-shaped.............................. Zerconopsis

4. Vertex of dorsal shield strongly arched downward, setae j1 concealed from above; peritremes sharply recurved distally; dorsal shield without midlateral incisions; tarsi II-IV with 1 (al1) or 2 (al1, pl1) dorso-lateral subapical setae very slender and elongate; palp tarsus with macroseta.............................. Iphidozercon
   - Vertex of dorsal shield not strongly arched downward, setae j1 visible from above; anterior extremities of peritremes not recurved; dorsal shield with or without midlateral incisions; tarsi II–IV with neither of dorso-lateral subapical setae slender and elongate; palp tarsus without macroseta .............................. Arctoseius

5. Dorsal shield lacking setae z1; epistome convex and smooth or slightly denticulate; genu I with 12 setae (av2 absent), tibia II with 9 setae (ad2 absent).............................. 6
   - Setae z1 present; tectum bi- or triramous; genu I with 13 setae, tibia II with 10 setae.............................. 7

6. Dorsal shield with midlateral incisions; all r–R marginal setae on soft cuticle flanking dorsal shield; female with: first pair of sternal setae on sternal shield, genital setae and pores on soft cuticle flanking epigynial shield, anal shield bearing only circum-anal setae.............................. Arctopsis
   - Dorsal shield lacking midlateral incisions; r–R marginal setae on edges of dorsal shield; female with: first pair of sternal setae on jugular plates separated from sternal shield or on margin of shield, genital setae and pores on epigynial shield, ventri-anal shield incorporating metapodal plates and bearing 4–5 pairs of setae in addition to circum-anal setae.............................. Neojordensia

7. Dorsal shield lacking setae z3, J2, S1; R3, R4 on dorsal shield, others (r6, R2, R5) absent; genu and tibia I each with 12 setae (av2 absent); genu III with 10 setae, tibia III with 9 setae (pl2 present on both); genu IV with 10 setae (pv1 present).............................. Arctoseoides
   - Dorsal shield holotrichous, with z3, J2, S1; 10–11 pairs of marginal r–R setae on soft cuticle laterally, none on dorsal shield; genu and tibia I each with 13 setae (av2 present); genu III with 8–9 setae, tibia III with 8 setae (pl2 absent on both); genu IV with 8–9 setae (pv1 absent).............................. Leioseius

References

• 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.
• 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 and Evans 1965Lindquist and Evans 1965:
  Lindquist EE, 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