Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Dense coating of cerotegument
• Podonotal shield and free marginal seta (or small plates) and pygidial shields under cerotegument
• <100 dorsal idiosomal setae
• Scabellum and pedofossae absent
• Sternal setae (st1–4) on sterno-parapodal-peritrematal shield that encompasses the genital opening anteriorly and laterally
• st5 usually on small latigynial shields (rarely fused to genital shield)
• Anal opening on ventrianal shield with 5 circumanal setae
• Genital shield usually nude, entirely intercoxal, without anterior median process
• Legs I without ambulacra, coxae I enlarged, but subcylindrical and widely separated; trochanter I with 4 setae; tibia I with 4 (rarely 3) dorsal and 2 ventral setae; all genu with 4 dorsal setae; genu II with 4 lateral setae.
• Chelicerae typically robust, elongate, with long snap-trap digits; corniculi elongate, bayonet-like.
• Tectum with strong median process; hypostomal denticles in rows to either side of furrow.
• Palp apotele 2-tined; palp genu with 4–5 setae, palp femur with 5 setae.
• Tritosternal laciniae typically fused, highly divided; tritosternal wider than long, usually rectangular
• Male genital opening intercoxal, valves without setae; chelicerae not obviously modified for sperm transfer

Key to adult females of common genera of Polyaspidoidea

1. Idiosoma and mesogynal shield oval to subrectangular; marginal shield fragmented.............................. 2
   - Idiosoma pyriform, mesogynal shield trapezoidal; marginal shield entire.............................. Trachytes

2. Genu IV with two ventral setae.............................. 3
   - Genu IV with one ventral seta.............................. Polyaspinus (+Uroseius)

3. Chelicerae and corniculi elongate, the latter reaching distal end of palpgenu.............................. Polyaspis (+Dyscritaspis)
   - Chelicerae and corniculi not elongate.............................. Dipolyaspis

Similar taxa

The combination of elongate snapping chelicerae, bayonet corniculi, and fragmented dorsal shields serve to distinguish Polyaspis from all others.

Ecology and distribution

Polyaspis mites are slow-moving, but effective predators that use their elongate chelicerae to 'snap-trap' more active microarthropods such as springtails. Polyaspis will also feed on nematodes.

References

• Ainscough 1981Ainscough 1981:
  Ainscough BD. 1981. Uropodine studies. I. Suprageneric classification in the cohort Uropodina Kramer, 1882 (Acari: Mesostigmata). International Journal of Acarology 7: 47–56.
• Athias 1976Athias 1976:
  Athias F. 1976. Observations morphologiques sur Polyaspis patavinus Berlese 1881 (Acariens: Uropodides). 2. Morphologie et chètotaxie des appendices au cours du dèveloppement postembryonnaire. Acarologia 18: 194–216.
• Camin 1953Camin 1953:
  Camin JH. 1953. A revision of the Cohort Trachytina Trägårdh, 1938, with the description of Dyscritaspis whartoni, a new genus and species of polyaspid mite from tree holes. Bulletin of the Chicago Academy of Sciences 9: 335–385.
• Camin 1954bCamin 1954b:
  Camin JH. 1954b. Polyaspis berlesei, a new species of trachytoid mite (Mesostigmata: Polyaspidae). Bulletin of the Chicago Academy of Sciences 10: 25–33.
• 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.
• Gilyarov and Bregatova 1977Gilyarov and Bregatova 1977:
  Gilyarov MS, Bregatova NG, eds. 1977. Handbook for the identification of soil-inhabiting mites, Mesostigmata. Zoological Institute of the Academy of Sciences, Petrograd.
• Karg 1989aKarg 1989a:
  Karg W. 1989a. Acari (Acarina), Milben Unterordnung Parasitiformes (Anactinotrichaeta) Uropodina Kramer, Schildkrötenmilben. Die Tierwelt Deutschlands 67: 1–203.
• 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.