Diagnostic characters:

• Female with 4 pairs of setae on a well sclerotized sternal shield

• 4 scleronoduli rarely present

• Tibia I and genu I each with 6/4 dorsal/ ventral setae.

Similar taxa.  The various families in the Rhodacaroidea are usually easy to distinguish from other Mesostigmata by their entire sternal shields with 4 pairs of setae and 6/4 dorsal/ ventral setation of tibia I.  In Rhodacaridae, most of which are small, lightly sclerotized mites, the anterior margin of the sternal shield is usually membranous to about the level of st1.  Digamasellidae have a highly reduced leg chaetome and a distinctive tectum with a subdorsal median tine.   Species of both Australian Rhodacaridae (except Protogamasellopsis) and Digamasellidae (Digamasellus) usually have 3-4 scleronoduli, but I know of only 1 undescribed Australian ologamasid with these light refracting podonotal structures.  Some Pachylaelapidae and Parholaspididae may have sternal shields that 'capture' st4, but both families have highly reduced leg chaetomes.

Diagnosis.  Tan, brown, orange or reddish dermanyssine mesostigmatans.  Females with separate podonotal and opisthonotal shields, fused to smoothly holodorsal shield, or beetle-like all encompassing armor, rarely encased in a layer of soil; males with holodorsal shield.  Peritremes typical running past coxa I, sometimes chambered; peritrematal shields usually well developed.  Female with large sternal shield bearing 4 pairs of setae (st1-4) and 3 pairs of lyrifissures (stp1-3), sometimes with arms embracing genital shield; genital shield usually mound-shaped to subrectangular, hinged at level of coxae IV, bearing 1 pair of setae, and free from ventrianal shield. Venter covered by large ventrianal shield, sometimes fused to peritrematal and/or dorsal shields; anal opening with 3 circumanal setae.  Tarsus I slender, sometimes elongate, with or without claws; trochanter I with 6 setae; tibia I with 6 dorsal and 4 ventral setae; genu IV with 5 dorsal and 2 ventral setae.  Chelicerae various, especially chelate-dentate and snapping; movable digit without excrescences.  Palp genu with 6 setae, palp apotele 3-tined; corniculi usually horn-like, rarely truncate and toothed; internal male highly divided.  Tritosternum biflagellate, with columnar base.  Tectum various, but typically including an elongate median process.  Female sperm induction pores at base of coxae IV, on coxae IV, on coxae or trochanters III, or other sites; sperm ducts lead to unpaired, central spermathecal sack (laelapid type).  Males with genital opening at base of tritosternum in sternogenital shield; spermatodactyl simple and finger-like to extremely complex; legs II commonly with femoral spur.  Deutonymphs with divided dorsal shield, rarely with acrotarsus (Euryparasitus), sometimes phoretic on mammals.

Ecology & Distribution.  Ologamasids are the dominant predatory mesostigmatans in forest litter in the Southern Hemisphere, but few species have been studied in detail (see Lee 1973, 1974).  Most are considered free-living predators, but species of Cyrtolaelaps and Euryparasitusare associated with mammal nests and their deutonymphs are phoretic on the nest builders.  Also, deutonymphs of the aberrant genera  Iphidosoma (often assigned to the Eviphididae) and Epiphis (often Rhodacaridae) are found on carabid beetles, and the former sometimes on sciarid flies.

References

Antony LM. 1987. A phylogenetic analysis of the Rhodacaroidea (Acari : Mesostigmata). Dissertation Abstracts International 47: 4047B.

Evans EO & 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.

Gilyarov MS & Bregatova NG (eds)  1977.  Handbook for the Identification of Soil-inhabiting Mites, Mesostigmata.  Zoological Institute of the Academy of Sciences: Petrograd [In Russian]

Lee DC. 1966. New species of Ologamasus Berlese (Acari : Rhodacaridae) from Australia and New Zealand. Records of the South Australian Museum 15: 205-235.

Lee DC. 1967. Heterogamasus Trägårdh (Acari: Rhodacaridae), including the subgenus Evanssellus Ryke, stat. n. Records of the South Australian Museum 15: 497-512.

Lee DC. 1970. The Rhodacaridae (Acari : Mesostigmata); classification, external morphology and distribution of genera. Records of the South Australian Museum 16: 1-219.

Lee DC. 1973. Rhodacaridae (Acari : Mesostigmata) from near Adelaide, Australia. I. Systematics. Records of the South Australian Museum 16: 1-36.

Lee DC. 1973. Rhodacaridae (Acari : Mesostigmata) from near Adelaide, Australia. II. Ecology. Transactions of the Royal Society of South Australia 97: 139-151.

Lee DC. 1974. Rhodacaridae (Acari : Mesostigmata) from near Adelaide, Australia. III. - Behaviour and development. Acarologia 16: 21-44.

Lee, D. C. 1977. Nomenclatural status of Cyrtolaelapidae, Ologamasinae and Gamasellinae (Acari : Mesostigmata). Journal of the Australian Entomological Society 16: 297-299.

Krantz GW.  1978.  A Manual of Acarology.  OSU Bookstores: Corvallis.

Krantz GW & Ainscough B.  1990.  Mesostigmata.  pp. 583-665, in DL Dindal (ed) Soil Biology Guide.  John Wiley & Sons: Brisbane.