Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Chelicera with well developed arthrodial brush
• Peritreme linear
• Free-living, not phoretic on insects

Diagnosis

Yellow to dark brown dermanyssine mesostigmatans with holodorsal shields. Peritremes generally well developed, shields sometimes produced posteriorly. Sternal shieldsternal shield:
a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
bearing 3 (rarely 4) pairs of setaeseta:
(pl. setae, from L. = bristle) cuticular process composed of a hollow shaft (sometimes filled with a refractive material) produced from a membranous socket (the alveolus); the hair-like, spine-like, branched or variously expanded structures on the surfaces of the legs and body.  Most setae function as mechanoreceptors, but others (e.g., solenidia) are chemoreceptors or have unknown or ambiguous functions.
(st1–3, 4) and 2–3 pairs of lyrifissures; metasternal shields present with st4 or fused to sternal or endopodal shields; genital shieldgenital shield:
a shield or shields covering the genital opening; in female mongynaspine Mesostigmata this shield is usually called the epigynal (epigynial) shield.  
mound-shaped, tongue-shaped, or broadly opisthogenital and bearing 1–2 (rarely more) pair of setaeseta:
(pl. setae, from L. = bristle) cuticular process composed of a hollow shaft (sometimes filled with a refractive material) produced from a membranous socket (the alveolus); the hair-like, spine-like, branched or variously expanded structures on the surfaces of the legs and body.  Most setae function as mechanoreceptors, but others (e.g., solenidia) are chemoreceptors or have unknown or ambiguous functions.
; ventrianal shieldventrianal shield:
in Mesostigmata, a ventral shield bearing the anal opening, circum anal setae, and one or more pairs of ventral setae or pores (lyrifissures) [see anal shield]; maybe rather narrow or very broad and covering most of the gaster.
broad with several pairs of ventral setaeseta:
(pl. setae, from L. = bristle) cuticular process composed of a hollow shaft (sometimes filled with a refractive material) produced from a membranous socket (the alveolus); the hair-like, spine-like, branched or variously expanded structures on the surfaces of the legs and body.  Most setae function as mechanoreceptors, but others (e.g., solenidia) are chemoreceptors or have unknown or ambiguous functions.
, sometimes fused to genital shields. Tarsustarsus:
(pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
I with or without claws; trochantertrochanter:
the leg segment between the coxa and the femur.
I with 6 setaeseta:
(pl. setae, from L. = bristle) cuticular process composed of a hollow shaft (sometimes filled with a refractive material) produced from a membranous socket (the alveolus); the hair-like, spine-like, branched or variously expanded structures on the surfaces of the legs and body.  Most setae function as mechanoreceptors, but others (e.g., solenidia) are chemoreceptors or have unknown or ambiguous functions.
; tibiatibia:
(pl. tibiae) the leg segment between the genu and the tarsus.
I with 5/3 dorsal/ ventral setaeseta:
(pl. setae, from L. = bristle) cuticular process composed of a hollow shaft (sometimes filled with a refractive material) produced from a membranous socket (the alveolus); the hair-like, spine-like, branched or variously expanded structures on the surfaces of the legs and body.  Most setae function as mechanoreceptors, but others (e.g., solenidia) are chemoreceptors or have unknown or ambiguous functions.
, genugenu:
(pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
I 5/2–3; genugenu:
(pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
IV with 9 setaeseta:
(pl. setae, from L. = bristle) cuticular process composed of a hollow shaft (sometimes filled with a refractive material) produced from a membranous socket (the alveolus); the hair-like, spine-like, branched or variously expanded structures on the surfaces of the legs and body.  Most setae function as mechanoreceptors, but others (e.g., solenidia) are chemoreceptors or have unknown or ambiguous functions.
, 4/1 dorsal/ ventralventral:
relating to the lower or under side; opposed to dorsal.
. Chelicerae chelate-dentatechelate-dentate:
pincer-like chelicerae with teeth.
, serrateserrate:
with closely set teeth that resemble the cutting edge of a saw.
, or snapping; movable digit without excrescences, but with well developed arthrodial brusharthrodial brush:
a brush like extension of the arthrodial membrane at the articulation of the movable and fixed digits in some Mesostigmata. Not to be confused with cheliceral excrescences that are produced from openings in the movable digit.
. 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 setaeseta:
(pl. setae, from L. = bristle) cuticular process composed of a hollow shaft (sometimes filled with a refractive material) produced from a membranous socket (the alveolus); the hair-like, spine-like, branched or variously expanded structures on the surfaces of the legs and body.  Most setae function as mechanoreceptors, but others (e.g., solenidia) are chemoreceptors or have unknown or ambiguous functions.
, 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.
3-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.
horn-like to bayonet-likebayonet-like:
resembling a long, sharp blade used for stabbing, as in some corniculi; sword-like.
. 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 columnar basebase:
the usually columnar basal part of the tritosternum; sometimes expanded and rectangular or otherwise modified; the most basal part of any structure.
. Tectumgnathotectum:
(= epistome, tectum) an often membranous dorsal projection of the anterior margin of the basis capitulum in Mesostigmata; often diagnostic at family-, genus- or species-levels; also often difficult to see without high magnification and good optics.
with long median process or denticulatedenticulate:
bearing small, sharp processes, e.g., the hypostome of ticks.
-trifurcate. Female sperm induction pores near bases of coxae IV.  Males with genital opening at basebase:
the usually columnar basal part of the tritosternum; sometimes expanded and rectangular or otherwise modified; the most basal part of any structure.
of 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.  
in sternogenital shield; spermatodactylspermatodactyl:
(also spermadactyl) the 'sperm finger' on the chelicerae of male dermanyssine Mesostigmata used to transfer sperm to the secondary sperm system in the female; spermatodactyls take various forms, from simple finger-like processes to very long, contorted structures.  
usually well developed.

Similar taxa

Macrochelids (recurved peritreme); pachylaelapids (lack arthrodial brush); Ologamasidae (tibia I with 6 dorsal setae); Laelapidae: Ololaelaps (lacks arthrodial brush).

References

• Evans 1956Evans 1956:
  Evans GO. 1956. On the classification of the family Macrochelidae with particular reference to the subfamily Parholaspinae (Acarina - Mesostigmata). Proceedings of the Zoological Society of London 127: 345-377.
• Halliday 1995Halliday 1995:
  Halliday RB. 1995. A new genus and two new species of Parholaspididae from Australia and Papua New Guinea (Acarina: Mesostigmata). In: Harvey MS, ed. Australasian spiders and their relatives: Papers honouring Barbara York Main. Records of the Western Australian Museum, Supplement 52: 209-217.