Mesostigmata

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Taxonomy

updated 2025

Diagnostic characters

• Female with 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.
  on the sternal shieldsternal shield:
  a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
  (st1 often in membranous area)
• 4 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
• Tibiatibia:
  (pl. tibiae) the leg segment between the genu and the tarsus.
  I and genugenu:
  (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
  I each 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.
  IV with 7 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/ventral
• Sperm induction porepore:
  a pore-like opening or structure in the cuticle.  In Mesostigmata, lyrifissures and true pore openings are often difficult to separate and both tend to be called 'pores', e.g., the sternal pores stp1-3.
  usually on leg III or IV, or at their 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.
  usually with median subdorsal process and a pair of lateral tines
• Opisthonotal shieldopisthonotal shield:
  the posterior shield in mesostigmatans with divided dorsal shields.
  often with median anterior notchnotch:
  a subrectagular to v-shape incision or similar form on the margin of a sclerite.
  or incisions, sometimes with posteriorposterior:
  the back part of the body or towards that region in comparison, e.g., 'posterior to'.
  horns; often capturing some of the R-series
• Deutonymphs phoretic on insects

Similar taxa

See also Digamasellus Berlese, Longoseius Chant. Dendrolaelaps species and related digamasellids are small, subrectangular mites that resemble some Rhodacaridae and Ascidae. Rhodacarids retain the 6/4 dorsal/ ventralventral:
relating to the lower or under side; opposed to dorsal.
setation of tibiatibia:
(pl. tibiae) the leg segment between the genu and the tarsus.
I, but Digamasellidae have 5/3 (as well as other reductions) and a distinctive 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 a subdorsal median tine. Ascine (e.g., Asca, Protogamasellus, Gamasellodes) and arctoseiine (e.g., Arctoseius) ascids also have 3 ventral setaeventral setae:
in the Lindquist-Evans system used in the Mesostigmata, the ventral region has up to three longitudinal rows (Jv, Zv, Lv) with 1-5 transverse row designations.
on tibiatibia:
(pl. tibiae) the leg segment between the genu and the tarsus.
I, but only 3 pairs of setae on their sternal shields, and lack an elongate median tine on their tectatectum:
(pl. tecta) any shelf-like projection of the cuticle.  In Mesostigmata the leading dorsal edge of the basis capitulum is referred to as the tectum, gnathotectum, or epistome.
.

Key to adult females of Rhodacarus-like mites
(Rhodacaridae, Ologamasidae, Digamasellidae, Ascidae)

1. Arthrodial process simplesimple:
   unadorned; simple setae are needle-like and without hairs or pectins.
   .............................. 4
   - Arthrodial process produced as a brush.............................. 2

2. Basitarsusbasitarsus:
   a basal subdivision of the tarsus.
   IV with 4 setae (pl4 present).............................. Pararhodacarus
   - Basitarsusbasitarsus:
   a basal subdivision of the tarsus.
   IV with 3 setae (pl4 absent).............................. 3

3. 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 single median process or dentate.............................. Afrogamasellus
   - 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 median stalk y-shaped, usually with lateral tines.............................. Afrodacarellus

4. Scleronoduli present.............................. 5
   - 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.............................. 10

5. Tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   I with 4 ventral setaeventral setae:
   in the Lindquist-Evans system used in the Mesostigmata, the ventral region has up to three longitudinal rows (Jv, Zv, Lv) with 1-5 transverse row designations.
   ; 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.............................. 6
   - Tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   I with 3 ventral setaeventral setae:
   in the Lindquist-Evans system used in the Mesostigmata, the ventral region has up to three longitudinal rows (Jv, Zv, Lv) with 1-5 transverse row designations.
   ; 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.............................. 9

6. 3 scleronoduli (median unpaired);  j1–2, z1, and s1 on anterior margin of podonotal shieldpodonotal shield:
   the anterior shield in mesostigmatans with divided dorsal shields.  
   .............................. 7
   - 4 scleronoduli (median pair +/- fused);  j1 (but not j2), z1 and s1 on anterior margin of shield.............................. 8

7. Pretarsustarsal apotele:
   (also pretarsus) the most distal segments of legs and palps bearing the claws and empodium
   I absent; without presternal plateletspresternal platelets:
   small sclerotized plates anterior to the sternal shield and laterad or posteriad the base of the tritosternum in some Mesostigmata.
   .............................. Rhodacarus (+Mediorhodacarus)
   - Pretarsustarsal apotele:
   (also pretarsus) the most distal segments of legs and palps bearing the claws and empodium
   I present; with 2 pairs of presternal plateletspresternal platelets:
   small sclerotized plates anterior to the sternal shield and laterad or posteriad the base of the tritosternum in some Mesostigmata.
   .............................. Rhodacaropsis

8. Podonotal shieldpodonotal shield:
   the anterior shield in mesostigmatans with divided dorsal shields.  
   entire.............................. Rhodacarellus
   - Podonotal shieldpodonotal shield:
   the anterior shield in mesostigmatans with divided dorsal shields.  
   divided between setae j3–j4; 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.
   denticulate-trifurcate.............................. Minirhodacarellus

9. Tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   I with 5 (rarely 4) dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   setae; 2 pairs of scleronoduliscleronoduli:
   3-4 light refractile structures, sometimes comma-shaped, in the podonotal region of many Rhodacaroidea and the genus Protogamasellus (Ascidae) in the Mesostigmata.  
   ; sternal shieldsternal shield:
   a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
   with 4 pairs of setae; anal opening normal.............................. Dendrolaelaps (Digamasellidae)
   - Tibiatibia:
   (pl. tibiae) the leg segment between the genu and the tarsus.
   I with 6 dorsaldorsal:
   relating to the upper or back side; opposed to ventral.
   setae; 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.  
   ; sternal shieldsternal shield:
   a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
   with 3 pairs of setae (st4 in soft cuticle); anal opening enlarged.............................. Protogamasellus mica Group (Ascidae)

10. Sternal seta st4 on sternal shieldsternal shield:
    a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
    .............................. 11
    - Sternal  seta st4 in soft cuticle.............................. 15

11. Anal opening large; tibiatibia:
    (pl. tibiae) the leg segment between the genu and the tarsus.
    I with 5 dorsaldorsal:
    relating to the upper or back side; opposed to ventral.
    setae.............................. Digamasellus (Digamasellidae)
    - Anal opening normal; tibiatibia:
    (pl. tibiae) the leg segment between the genu and the tarsus.
    I with 6 dorsaldorsal:
    relating to the upper or back side; opposed to ventral.
    setae.............................. 12

12. Sternal shieldsternal shield:
    a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
    strongly sclerotized throughout; tibiatibia:
    (pl. tibiae) the leg segment between the genu and the tarsus.
    I with 4 ventral setaeventral setae:
    in the Lindquist-Evans system used in the Mesostigmata, the ventral region has up to three longitudinal rows (Jv, Zv, Lv) with 1-5 transverse row designations.
    .............................. Geogamasus (Ologamasidae)
    - Anterior region of sternal shieldsternal shield:
    a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
    poorly sclerotized, setae st1 in soft or granulate cuticle; tibiatibia:
    (pl. tibiae) the leg segment between the genu and the tarsus.
    I with 3 ventral setaeventral setae:
    in the Lindquist-Evans system used in the Mesostigmata, the ventral region has up to three longitudinal rows (Jv, Zv, Lv) with 1-5 transverse row designations.
    .............................. 13

13. 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; coxacoxa:
    the basal segment of the leg, articulating with (Parasitiformes) or fused to (Acariformes) the body wall.
    I without dorsaldorsal:
    relating to the upper or back side; opposed to ventral.
    spine .............................. 15
    - Palpapotele 3-tined: coxacoxa:
    the basal segment of the leg, articulating with (Parasitiformes) or fused to (Acariformes) the body wall.
    I with dorsaldorsal:
    relating to the upper or back side; opposed to ventral.
    spine.............................. 14

14. Presternal area granulate.............................. Protogamasellopsis
    - Presternal area with paired stacks of 4 presternal plateletspresternal platelets:
    small sclerotized plates anterior to the sternal shield and laterad or posteriad the base of the tritosternum in some Mesostigmata.
    .............................. Rhodacarella

15. Posteriorposterior:
    the back part of the body or towards that region in comparison, e.g., 'posterior to'.
    margin of podonotalpodonotal:
    relating to the dorsal podosoma, the region of the idiosoma over the legs.
    (at j6) and anterior margin of opisthonotalopisthonotal:
    dorsal opisthosoma.
    (at J1) shields with transverse lines; genugenu:
    (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
    IV with 8 setae, tibiatibia:
    (pl. tibiae) the leg segment between the genu and the tarsus.
    IV with 9 setae.............................. Protogamasellus hibernicus Group (Ascidae)
    - Podonotalpodonotal:
    relating to the dorsal podosoma, the region of the idiosoma over the legs.
    and opisthonotalopisthonotal:
    dorsal opisthosoma.
    shields without transverse lines; genugenu:
    (pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
    IV with 9 setae, tibiatibia:
    (pl. tibiae) the leg segment between the genu and the tarsus.
    IV with 10 setae.............................. Gamasellodes (Ascidae)

Diagnosis of Digamasellidae

Tan, pink to reddish dermanyssine mesostigmatans with subequal podonotalpodonotal:
relating to the dorsal podosoma, the region of the idiosoma over the legs.
(18–23 pairs of setae) and opisthonotalopisthonotal:
dorsal opisthosoma.
(15–19 pairs of setae) shields, the latter sometimes with horn-like processes; 2 pairs of scleronoduliscleronoduli:
3-4 light refractile structures, sometimes comma-shaped, in the podonotal region of many Rhodacaroidea and the genus Protogamasellus (Ascidae) in the Mesostigmata.  
often present. Peritremes short or long. Female with entire sternal shieldsternal shield:
a shield in the anterior intercoxal region of parasitiform mites that bears one or more pairs of sternal setae.
bearing 4 pairs of setae (st1–4) (st4 in soft cuticle in Longoseius) and 3 pairs of lyrifissures (stp1–2), anterior region usually +/- membranous; metasternal shields absent; genital shieldgenital shield:
a shield or shields covering the genital opening; in female mongynaspine Mesostigmata this shield is usually called the epigynal (epigynial) shield.  
usually trapezoidal to subrectangular and bearing 1 pair of setae; 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, bearing 2–6 pairs of ventral setaeventral setae:
in the Lindquist-Evans system used in the Mesostigmata, the ventral region has up to three longitudinal rows (Jv, Zv, Lv) with 1-5 transverse row designations.
and 3 circumanal setaecircumanal setae:
in Mesostigmata, the three setae (postanal and pair of peranal) setae surrounding the anal opening.
, sometimes fused to opisthonotal shieldopisthonotal shield:
the posterior shield in mesostigmatans with divided dorsal shields.
; anal opening sometimes enlarged (Digamasellus). Tarsustarsus:
(pl. tarsi) the subdistal leg segment between the tibia and the pretarsus (apotele).
I with claws; trochantertrochanter:
the leg segment between the coxa and the femur.
I with 6 setae; tibiatibia:
(pl. tibiae) the leg segment between the genu and the tarsus.
and genugenu:
(pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
I each with 5/3 dorsal/ventral setae; genugenu:
(pl. genua) (= patella) the 4th leg segment, between the femur and tibia.
IV with 7 setae, 4/1 dorsal/ventral. Chelicerae chelate-dentatechelate-dentate:
pincer-like chelicerae with teeth.
to serrateserrate:
with closely set teeth that resemble the cutting edge of a saw.
; movable digit without excrescences. 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.
horn-like (forked in some males). 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 2 subequal lateral tines and usually a median prong originating from the underside. Female sperm induction pores on legs III or IV or at their bases. 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 with st5 on separate or partially detached subtriangularsubtriangular:
more or less triangular.  
plates; 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 S-shaped.

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 setae.............................. Longoseius
   - Bodybody:
   the idiosoma of mites.
   subrectangular to oval in shape; trochantertrochanter:
   the leg segment between the coxa and the femur.
   III with 5 setae.............................. 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 setae z5; anal opening normal; seta 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; seta 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 spatulatespatulate:
   (Latin spatula = spoon) spatula-shaped; variously interpreted, but usually referring to setae that are flattened and somewhat expanded distally.
   setae; setae j2 inserted well behind setae 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; setae 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 species of Dendrolaelaps that have been studied are predators on small invertebrates such as nematodes and some feed on the eggs and larvae of bark beetles. Some are free-living in soil, but many are associated with insects (e.g., sciarid flies, dung beetles, bark beetles) that are found in boles, logs, and other woody debris and their associated fungi.

References

• 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.
• McGraw and Farrier 1969McGraw and Farrier 1969:
  McGraw JR and Farrier MH. 1969. Of the superfamily Parasitoidea (Acarina: Mesostigmata) associated with Dendroctonus and Ips (Coleoptera: Scolytidae). North Carolina Agricultural Experiment Station Technical Bulletin No. 192, 162 pp.
• 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.