Mesostigmata

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Taxonomy

Diagnostic characters

• Adult female with 4 pairs of setae on the sternal shield
• Dorsal shield divided, 4 scleronoduli  on pododnotal shield
• Tibia I with 6/4 and genu I with 6/3 dorsal/ventral setae; genu IV with 10 setae, 5/2 dorsal/ventral
• Chelicerae usually with arthrodial brush

Similar taxa

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

1. Arthrodial process simple.............................. 4
   - Arthrodial process produced as a brush.............................. 2

2. Basitarsus IV with 4 setae (pl4 present).............................. Pararhodacarus
   - Basitarsus IV with 3 setae (pl4 absent).............................. 3

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

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

5. Tibia I with 4 ventral setae; palp apotele 3-tined.............................. 6
   - Tibia I with 3 ventral setae; palp apotele 2-tined.............................. 9

6. 3 scleronoduli (median unpaired);  j1–2, z1, and s1 on anterior margin of podonotal shield.............................. 7
   - 4 scleronoduli (median pair +/- fused);  j1 (but not j2), z1 and s1 on anterior margin of shield.............................. 8

7. Pretarsus I absent; without presternal platelets.............................. Rhodacarus (+Mediorhodacarus)
   - Pretarsus I present; with 2 pairs of presternal platelets.............................. Rhodacaropsis

8. Podonotal shield entire.............................. Rhodacarellus
   - Podonotal shield divided between setae j3–j4; tectum denticulate-trifurcate.............................. Minirhodacarellus

9. Tibia I with 5 (rarely 4) dorsal setae; 2 pairs of scleronoduli; sternal shield with 4 pairs of setae; anal opening normal.............................. Dendrolaelaps (Digamasellidae)
   - Tibia I with 6 dorsal setae; 3 scleronoduli; sternal shield with 3 pairs of setae (st4 in soft cuticle); anal opening enlarged.............................. Protogamasellus mica Group (Ascidae)

10. Sternal seta st4 on sternal shield.............................. 11
    - Sternal  seta st4 in soft cuticle.............................. 15

11. Anal opening large; tibia I with 5 dorsal setae.............................. Digamasellus (Digamasellidae)
    - Anal opening normal; tibia I with 6 dorsal setae.............................. 12

12. Sternal shield strongly sclerotized throughout; tibia I with 4 ventral setae.............................. Geogamasus (Ologamasidae)
    - Anterior region of sternal shield poorly sclerotized, setae st1 in soft or granulate cuticle; tibia I with 3 ventral setae.............................. 13

13. Palp apotele 2-tined; coxa I without dorsal spine .............................. 15
    - Palpapotele 3-tined: coxa I with dorsal spine.............................. 14

14. Presternal area granulate.............................. Protogamasellopsis
    - Presternal area with paired stacks of 4 presternal platelets.............................. Rhodacarella

15. Posterior margin of podonotal (at j6) and anterior margin of opisthonotal (at J1) shields with transverse lines; genu IV with 8 setae, tibia IV with 9 setae.............................. Protogamasellus hibernicus Group (Ascidae)
    - Podonotal and opisthonotal shields without transverse lines; genu IV with 9 setae, tibia IV with 10 setae.............................. Gamasellodes (Ascidae)

References

• Athias-Henriot 1961aAthias-Henriot 1961a:
  Athias-Henriot C. 1961a. Mesostigmatides (Urop. excl.) edaphiques Mediterraneans (Acaromorpha, Anactinotrichida). Acarologia 3: 381–509.
• Hurlbutt 1973Hurlbutt 1973:
  Hurlbutt HW. 1973. The Afrogamasellus Loots and Ryke and Afrodacarellus n. gen. (Acarina: Rhodacaridae) of Tanzania. Acarologia 15: 565–619.
• Lee 1970Lee 1970:
  Lee DC. 1970. The Rhodacaridae (Acari: Mesostigmata); classification, external morphology and distribution of genera. Records of the South Australian Museum 16: 1–219.
• Loots 1969Loots 1969:
  Loots GC. 1969. Notes on Rhodacarus Oudemans and its related genera with descriptions of new species from the Ethiopian region. Publicações Culturais da Companhia de Diamantes de Angola 81: 45–82.
• Moraza 2004Moraza 2004:
  Moraza ML. 2004. Rhodacarella, a new genus of Rhodacaridae mites from North America (Acari: Mesostigmata: Rhodacaridae). Zootaxa 470: 1–10.