Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Completely divided dorsal shield without transverse lines extending across surface
• Podonotal shield with 13 pairs of setae (j2, z1–3 absent; s1–2, r2–5 in soft cuticle laterad shield)
• Opisthonotal shield with 12 pairs of setae (J3, Z2, S1 absent), R1–5 in soft cuticle
• Small anal shield with only circumanal setae, paranal setae inserted closer to posterior margin of anus than to anterior margin
• Genu and tibia I with only 4 dorsal setae; genu IV with 7 setae (pl1 present; al2, pd3 absent); tibia IV with 7 setae (al2, pl2, pd3 absent).
• Sternal pore 3 on sternal shield; setae Z5 whip-like
• Gnathotectum rounded, denticulate

Similar taxa

Similar taxa not in Lucid key (see below). See key to small Rhodacarus-like mites.

Similar taxa in key. Gamasellodes Athias-Henriot, Protogamasellus Karg

Key to genera in the subfamily Ascinae

1. With holodorsal shield that captures the R-series.............................. 2
   - Dorsal shield divided into two subequal shields; R-series setae in softcuticle.............................. 3

2. Seta z1 present laterad seta j1 on anterior median region of dorsal shield; femur III with 7 setae; genu I with 13 setae; tibia II with 10 setae.............................. Orthadenella (Blattisociidae)
   - Seta z1 absent; femur III with 6 setae; genu I with 12 setae; tibia II with 9 setae.............................. Neojordensia

3. Opisthonotal shield with 12 pairs of setae (J3, Z2, S1 absent); podonotal shield lacking setae j2, z1, z3; adult leg setation strongly neotenous, genua I–II–III–IV with 11–8–7–7 setae, tibiae with 11–7–7–7 setae; female with anal shield.............................. Diseius
   - Opisthonotal shield with 15 or more pairs of setae (J3, Z2, S1 present); podonotal shield with setae j2, z3, sometimes z1; adult leg setation not strongly neotenous, minimum number of setae on genua 12–11–8–8, on tibiae 13–10–8–9; female with anal or ventrianal shield.............................. 4

4. Hypostome with corniculi bifid apically; anterior rostral setae thickened, spinelike; dorsal shield setae z1 absent.............................. Anephiasca
   - Hypostome with corniculi entire apically; anterior rostral setae of similar thickness to other hypostomal setae; dorsal shield setae z1 present or absent.............................. 5

5. Female with epigynial shield strongly rounded posteriorly and with small subtriangular ventrianal or anal shield bearing 3–5 setae; male with ventrianal shield united to peritrematal shields; soft body cuticle often with microtuberculate striae.............................. 6
   - Female with epigynial shield truncate posteriorly and usually with well developed ventrianal shield (rarely anal shield) bearing 3–9 setae (including circumanal setae); male with ventrianal shield separate from peritrematal shields; soft body cuticle striae without microtubercles.............................. 8

6. Palps elongated, at least half as long as leg I; palp trochanter longer than femur; palp tibia almost 3 times as long as tarsus.............................. Anystipalpus
   - Palps of normal length, about one-third as long as leg I; palp trochanter slightly shorter than femur; palp tibia twice as long as tarsus.............................. 7

7. Legs I with ambulacra and claws.............................. Antennoseius (Vitzthumia)
   - Legs I without ambulacra and claws.............................. Antennoseius (Antennoseius)

8. Opisthonotal shield with setae Z4 & S5 usually approximate and inserted together on pair of prominent posterolateral tubercles; podonotal shield lacking setae z1,  j2 well behind level of j1; peritrematal shields of adults broad, truncate posteriorly; genu I with 12 setae (av2 absent).............................. Asca
   - Opisthonotal shield with setae Z4, S5 well separated, not borne on pair of strong tubercles; podonotal shield with setae z1 present; j2 tending to be displaced anteriorly, often in approximately transverse row with z1 and j1; peritrematal shields of adults narrow or of moderate width, tapering posteriorly; genu I with 13 setae (av2 present).............................. 9

9. Podonotal shield with transverse line extending across surface at level of setae z6, opisthonotal shield with similar line at level of setae J1; paranal setae inserted close to anterior margin of anus; genu IV with 8 setae (pl1 absent); tibia IV with 9 setae (pl2 absent).............................. Protogamasellus
   - Dorsal shields without transverse lines extending completely across surface; paranal setae inserted closer to posterior margin of anus than to anterior margin; genu IV with 9 setae (pl1 present); tibia IV with 10 setae (pl2 present).............................. 10

10. Sternal pore 3 in soft cuticle; setae r3 and Z5 club-shaped, densely plumose; gnathotectum denticulate; movable digit of chelicerae serrate.............................. Ectoantennoseius
    - Sternal pore 3 on sternal shield; setae r3 and Z5 setiform, smooth to barbed; gnathotectum more or less smoothly trifurcate; movable digit of chelicerae usually with 4–6 teeth, not serrate.............................. Gamasellodes

Ecology and distribution

These mites are poorly known inhabitants of tree bark.

References

• Karg 1993Karg 1993:
  Karg W. 1993. Acari (Acarina), Milben Parasitiformes (Anactinochaeta) Cohors Gamasina Leach, Raubmilben. Die Tierwelt Deutschlands 59: 1–523.
• 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