Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Adults with holodorsal shield lacking seta J3
• Subcordate ventrianal shield with 13 setae (ZV1–2, JV1–3 + circumanals)
• Genital shield truncate posteriorly and bearing 1 pair of setae
• Sternal shield with 3 pairs of setae and convex posterior margin
• Metasternal setae on metasternal-endopodal shield that is fused anteriorly to sternal shield
• Peritrematal shield extending beyond coxae IV
• Arthrodial brush vestigial
• Palp apotele with 3-tines; tibia I with 6 dorsal setae; tibia III with 8 dorsal setae; tibia IV with 8 dorsal setae.

Similar taxa

Species of Pachyseius have spurs on tarsi II and have st4 on a metasternal shield or in the soft cuticle. Species of Macrocheles have recurved 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 spur-like distal setae on tarsus II.............................. 3
   - Spur-like setae on tarsus II absent.............................. 2

2. Female with subcordate ventrianal shield with 13 setae (ZV1–2, JV1–3 + circumanals); genital shield truncate posteriorly and bearing 1 pair of setae; sternal shield with 3 pairs of setae and convex posterior margin; metasternal setae on metasternal-endopodal shield; free-living or on dung beetles.............................. Zygoseius
   - Female with anal shield (rarely capturing 1–2 ventral setae); opisthogenital shield spreading laterally, with 2 pairs of setae and recurved posterior margin; associated with ants.............................. Sphaerolaelaps

3. Female sternal shield bearing 4 pairs of setae, opisthogenital shield with 2 or more pairs of setae, and anal shield with 3 circumanal setae.............................. 4
   - Female sternal shield bearing 3 pairs of setae (st4 on small metasternal shield or in soft cuticle), genital shield with 1 pair of seta, and ventrianal shield with 7–10 setae.............................. Pachyseius

4. Tibia I with 5 dorsal setae; palp apotele 3-tined.............................. 5
   - Tibia I with 6 dorsal setae; palp apotele 2-tined.............................. 6

5. Genu I with 5 dorsal setae.............................. Onchodellus
   - Genu I with 6 dorsal setae.............................. Pachylaelaps

6. Seta st4 on small metasternal plate; dorsal shield with 37 pairs of setae.............................. Pachyseiulus
   - Seta st4 on in soft cuticle; dorsal 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.