Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Grey-brown to red (when blood engorgedengorged:
  swollen from feeding as in a tick or chigger.
  ) or black parasitic dermanyssine mesostigmatans with a truncate dorsaldorsal:
  relating to the upper or back side; opposed to ventral.
  shield covering the podonotalpodonotal:
  relating to the dorsal podosoma, the region of the idiosoma over the legs.
  region and two pairs of small scutellaescutella:
  (pl scutellae) small shields or platelets.
  in the mesonotal region and a small, subcircular pygidial shieldpygidial shield:
  (pygidial sclerite) in Mesostigmata, a shield at the back end of the idiosoma.
  
• Sternal shieldsternal shield:
  a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
  entire to eroded sternal shieldsternal shield:
  a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
  bearing 2 pairs of setae
• Genital shieldgenital shield:
  a shield or shields covering the genital opening; in female mongynaspine Mesostigmata this shield is usually called the epigynal (epigynial) shield.  
  dagger-shaped, nude
• st3–5 in soft cuticle
• Anal shield small, with 3 circumanal setaecircumanal setae:
  in Mesostigmata, the three setae (postanal and pair of peranal) setae surrounding the anal opening.
  
• Some ventralventral:
  relating to the lower or under side; opposed to dorsal.
  and lateral hypertrichy present
• Chelicerae elongate and edentateedentate:
  with out teeth; usually referring to chelicerae.
  stylets
• Palppalp:
  (= pedipalp) the second pair of limbs in arachnids, used in feeding and originating on either side of the chelicerae.  In mites, the palps may be vestigial, with only a few segments, or have a maximum of  5 freely articulating segments (rarely the femur is subdivided) and a distal or subdistal apotele.
  genu with 6 setae, palp apotelepalptarsal apotele:
  (= palp apotele, palptarsal claw) the most distal segment of the palp; absent in Acariformes, claw-like in Opilioacarida, and a subdistal, tined structure in the Mesostigmata.
  2-tined; corniculicorniculus:
  (pl. corniculi) (also, external malae) a usually horn-like process (sometimes toothed, bifurcate, trifurcate, spine-like, spatulate, or membranous) on the subcapitulum of parasitiform mites that usually supports the salivary styli.  A toothed corniculus could be confused with a rutellum, a possibly homologous structure in Acariformes and Opilioacarida. Phytoseiid image is spatulate corniculus.
  membranous.
• Tritosternumtritosternum:
  the sternum of the 3rd body segment (between legs I); produced as a biflagellate structure in Mesostigmata, although sometimes the flagellae (laciniae) are partially or completely fused.  
  biflagellate with denticulatedenticulate:
  bearing small, sharp processes, e.g., the hypostome of ticks.
  membranous margin
• Dorsaldorsal:
  relating to the upper or back side; opposed to ventral.
  shield truncate, opisthonotum exposed

Similar taxa

Laelapid mites are similar, but lack the expanded margins of the tritosternal laciniae and usually have well developed corniculicorniculus:
(pl. corniculi) (also, external malae) a usually horn-like process (sometimes toothed, bifurcate, trifurcate, spine-like, spatulate, or membranous) on the subcapitulum of parasitiform mites that usually supports the salivary styli.  A toothed corniculus could be confused with a rutellum, a possibly homologous structure in Acariformes and Opilioacarida. Phytoseiid image is spatulate corniculus.
(horn- to bayonet-shaped). Species of Macronyssus have more extensive dorsaldorsal:
relating to the upper or back side; opposed to ventral.
shields.

Similar taxa not in key. Five other families of Mesostigmata are found on reptiles, but none have the dorsaldorsal:
relating to the upper or back side; opposed to ventral.
shielding reduced to a podonotal shieldpodonotal shield:
the anterior shield in mesostigmatans with divided dorsal shields.  
. Members of three other families of Dermanyssoidea have been described from reptiles: Entonyssidae (in respiratory tract; lightly sclerotized; peritremes absent), Omentolaelapidae (bodybody:
the idiosoma of mites.
reniform, venterventer:
the lower or under side; opposed to dorsum.
with a fringe of flattened setae), and Ixodorhynichidae (entireentire:
a shield or sclerite with a continuous margin without incisions.
or incised dorsaldorsal:
relating to the upper or back side; opposed to ventral.
shield; palp apotelepalptarsal apotele:
(= palp apotele, palptarsal claw) the most distal segment of the palp; absent in Acariformes, claw-like in Opilioacarida, and a subdistal, tined structure in the Mesostigmata.
reduced, 1-tined). Several kinds of trigynaspid mites (with several genital shields) also are associated with snakes and large lizards, especially species of Ophiomegistus and Ophiocelaeno.

Ecology and distribution

The snake mite, Ophionyssus natricis, is a major pest in zoos and has spread to wild snakes and skinks.

References

• Domrow 1988Domrow 1988:
  Domrow R. 1988. Acari Mesostigmata parasitic on Australian vertebrates: An annotated checklist, keys and bibliography. Invertebrate Taxonomy 1: 817-948.
• Evans and Till 1979Evans and Till 1979:
  Evans EO and 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.
• Krantz 1978Krantz 1978:
  Krantz GW. 1978. A manual of acarology [2nd ed.]. Oregon State University Book Stores, Corvallis.