Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Female sternal shield bearing 3 pairs of setae (st4 on small metasternal shield or in soft cuticle)
• Genital shield truncate posteriorly, with 1 pair of seta
• Ventrianal shield narrow to subcordate and with 7–10 setae
• Peritrematal shield not extending beyond coxae IV

Similar taxa

Species of Zygoseius lack spurs on tarsi II and have st4 on metasternal-endopodal plates. Species of Macrocheles have recurved peritremes.

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

• Moraza 1993Moraza 1993:
  Moraza ML. 1993. Two new species of Pachyseius Berlese, 1910 from Spain (Acari, Mesostigmata: Pachylaelapidae). Acarologia 34: 89–94.
• Moraza and Johnston 1990Moraza and Johnston 1990:
  Moraza ML, Johnston DE. 1990. Pachyseiulus hispanicus n. gen., n. sp., from Navarre (northern Spain) (Acari: Mesostigmata: Pachylaelapidae). International Journal of Acarology 16: 213–218.
• Yin et al. 1986Yin et al. 1986:
  Yin S-G, Luc J, Lian W-H. 1986. A new species and a new record of the genus Pachyseius from China (Acarina: Pachylaelapidae). Acta Zootaxonomica Sinica 11 (2): 191–193.