Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

(NB—the deutonymphdeutonymph:
(also deuteronymph) the second nymphal stage or instar.
has been confused with adult female in several papers)

• Bodybody:
  the idiosoma of mites.
  extremely narrow and elongate and with two dorsaldorsal:
  relating to the upper or back side; opposed to ventral.
  shields; podonotal shieldpodonotal shield:
  the anterior shield in mesostigmatans with divided dorsal shields.  
  deeply incised
• Podonotal shieldpodonotal shield:
  the anterior shield in mesostigmatans with divided dorsal shields.  
  with 12 pairs of setae; opisthonotalopisthonotal:
  dorsal opisthosoma.
  with 14–15 pairs (+/- J2); R1, 4, 5 in soft cuticle.
• Female with sternal shieldsternal shield:
  a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
  split medially by soft cuticle, st1–2 and st3–4 on separate halves
• Scleronoduliscleronoduli:
  3-4 light refractile structures, sometimes comma-shaped, in the podonotal region of many Rhodacaroidea and the genus Protogamasellus (Ascidae) in the Mesostigmata.  
  absent or vestigial between setae z5
• Leg setation highly deficientdeficient:
  in relation to setae, reduced from a presumed holotrichous number.
  , including trochantertrochanter:
  the leg segment between the coxa and the femur.
  I with only 5 setae; trochantertrochanter:
  the leg segment between the coxa and the femur.
  III with 4 setae; the palpgenu with only 5 setae.
• Peritremeperitreme:
  a groove or gutter on the surface connecting to a stigmatal opening.  In Mesostigmata the peritremes are lateral and run above the coxae of the legs and usually run to near the anterior margin of the idiosoma, but they may be very short or vestigial.  In Prostigmata peritremes are usually found on the anterior margin of the idiosoma, as short processes to either side of the capitulum (emergent peritremes), or as simple to complex lines or reticulations of short, connected chambers on the dorsal surface of the chelicerae or stylophore.
  in adults very short (restricted to coxacoxa:
  the basal segment of the leg, articulating with (Parasitiformes) or fused to (Acariformes) the body wall.
  IV region), but elongate (to seta z4) in deutonymphs

Similar taxa

Other extremely narrow and elongate mesostigmatans are typically found in the pores of polypore fungi and have a holodorsal shieldholodorsal shield:
a shield that covers all of the dorsum.  In Mesostigmata, the holodorsal shield is often interpreted as resulting from the fusion of podonotal and opisthonotal shields and a suture between these regions is often visible (see recurved and procurved).
, e.g., see Mycolaelaps and Hoploseius tenuis. Although less elongate, some species of Protogamasellus and Protogamasellopsis somewhat resemble Longoseius (Longoseius) but have fuller setation, including setaseta:
(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.
z1 and j2 aligned with j1 on the anterior margin of the podonotal shieldpodonotal shield:
the anterior shield in mesostigmatans with divided dorsal shields.  
. Species of Longoseius (Longoseiulus) are less narrow and have scleronoduliscleronoduli:
3-4 light refractile structures, sometimes comma-shaped, in the podonotal region of many Rhodacaroidea and the genus Protogamasellus (Ascidae) in the Mesostigmata.  
and podonotalpodonotal:
relating to the dorsal podosoma, the region of the idiosoma over the legs.
shields with full complements of j, z, and s 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.
.

Key to genera of Digamasellidae

1. Bodybody:
   the idiosoma of mites.
   extremely narrow and elongate, length 2.5–4 times width; trochantertrochanter:
   the leg segment between the coxa and the femur.
   III with 4 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.
   .............................. Longoseius
   - Bodybody:
   the idiosoma of mites.
   subrectangular to oval in shape; trochantertrochanter:
   the leg segment between the coxa and the femur.
   III with 5 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.
   .............................. 2

2. Scleronoduliscleronoduli:
   3-4 light refractile structures, sometimes comma-shaped, in the podonotal region of many Rhodacaroidea and the genus Protogamasellus (Ascidae) in the Mesostigmata.  
   present under podonotal shieldpodonotal shield:
   the anterior shield in mesostigmatans with divided dorsal shields.  
   between 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.
   z5; anal opening normal; setaseta:
   (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.
   z3 present on podonotal shieldpodonotal shield:
   the anterior shield in mesostigmatans with divided dorsal shields.  
   .............................. 3
   - Scleronoduliscleronoduli:
   3-4 light refractile structures, sometimes comma-shaped, in the podonotal region of many Rhodacaroidea and the genus Protogamasellus (Ascidae) in the Mesostigmata.  
   absent; anal opening large; setaseta:
   (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.
   z3 absent from podonotal shieldpodonotal shield:
   the anterior shield in mesostigmatans with divided dorsal shields.  
   .............................. Digamasellus

3. Movable digit of female usually with 4 or more teeth; subcapitulumsubcapitulum:
   (also infracapitulum) the venter of the capitulum; the ventral faces of the fused palpcoxae; apparently formed independently in the two superorders of mites.
   with 5 rows of denticlesdenticles:
   small tooth-like processes, e.g., on the subcapitula of ticks and many mesostigmatans.
   .............................. 4
   - Movable digit of female with 3 teeth; subcapitulumsubcapitulum:
   (also infracapitulum) the venter of the capitulum; the ventral faces of the fused palpcoxae; apparently formed independently in the two superorders of mites.
   with 6 rows of denticlesdenticles:
   small tooth-like processes, e.g., on the subcapitula of ticks and many mesostigmatans.
   .............................. Dendroseius

4. Opisthonotal shieldopisthonotal shield:
   the posterior shield in mesostigmatans with divided dorsal shields.
   truncate or bilobed posteriorly and often with several pairs of spatulate 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.
   ; 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.
   j2 inserted well behind 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.
   j1–z1 on podonotal shieldpodonotal shield:
   the anterior shield in mesostigmatans with divided dorsal shields.  
   .............................. Dendrolaelaspis
   - Opisthonotal shieldopisthonotal shield:
   the posterior shield in mesostigmatans with divided dorsal shields.
   convex posteriorly and usually notched anteriorly; 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.
   j2 more or less aligned with j1–z1 on podonotal shieldpodonotal shield:
   the anterior shield in mesostigmatans with divided dorsal shields.  
   .............................. Dendrolaelaps

Ecology and distribution

The two described species of Longoseius (L. cuniculus Chant; L. longus (Hirschmann)) are found beneath bark in association with wood boring beetles.

References

• Chant 1961Chant 1961:
  Chant DA. 1961. A new genus and species of mite in the family Digamasellidae Evans (Acarina). Acarologia 3: 11–13.
• Kinn 1984Kinn 1984:
  Kinn DN. 1984. Life cycle of Dendrolaelaps neodisetus (Mesostigmata: Digamasellidae), a nematophagous mite associated with pine bark beetles (Coleoptera: Scolytidae). Environmental Entomology 13 (4): 1141-1144.
• Lindquist 1975Lindquist 1975:
  Lindquist EE. 1975. Digamasellus Berlese, 1905, and Dendrolaelaps Halbert, 1915, with descriptions of new taxa of Digamasellidae (Acarina: Mesostigmata). The Canadian Entomologist 107: 1-43.
• Womersley 1954bWomersley 1954b:
  Womersley H. 1954b. Two new species of mites (Acarina: Mesostigmata: Ascidae) associated with bark-boring beetles from South Australia. Records of the South Australian Museum 11: 113-116.