Gymnodamaeidae Grandjean, 1954

Walter, David Evans, 2009, Genera of Gymnodamaeidae (Acari: Oribatida: Plateremaeoidea) of Canada, with notes on some nomenclatorial problems, Zootaxa 2206, pp. 23-44 : 25

Gymnodamaeidae Grandjean, 1954 a

Diagnosis: Adult. Non-poronotic brachypyline oribatid mites with smooth to lightly rugose cuticle and thick coating of cerotegument with emergent, crystalloid pustules on body, legs, and setae. Notogaster typically flattened to concave and with raised rim (somewhat convex in Adrodamaeus ); anterior margin simple, or with short tubercles ( Adrodamaeus , Jacotella ) or median tubercular patch ( Pleodamaeus ); without scalps (except rarely in recently moulted individuals); bearing 2–3 pairs of dorsal lyrifissures (im, ip; ia present or obscure/ absent), 2 pairs (ips, ih) on the lateral aspect of the notogastral rim, pair of gland openings, and maximum of 6 pairs of posterior setae (h 1-3, p 1-3) (h 3 present in only one known species); sejugal tubercle (Sp) obscure or absent to spine-like and almost meeting pedotectum II; cerotegument with crystalline waxy pustules and often with a simple to complex pattern of folds, ridges and cells. Prodorsum without lamellae or costulae, but often with tubercles and ridges and covered by thick, pustulate cerotegument (sometimes with X-shaped raised area); with 5 pairs of setae (bo, ex, in, le, ro): interlamellar seta (in) short, spine-like, usually inserted on an apophysis; sensillus (bo) typically with a long stalk branched distally and covered in crystalline cerotegument that forms a paddle-like head covered in coarse denticles or barbs (Fig. 33); transverse prelamellar ridge posteriad insertions of lamellar setae (le) weakly to strongly developed; pedotectum I auriculate; pedotectum II auriculate, rounded or drawn-out and pointed distally ( Fig. 31 ); propodolateral tubercle (P) absent; postbothridial tubercle (Bp) variously developed. Legs and their setae covered in pustulate cerotegument; all pretarsi tridactyl and inserted on a stalk-like pedicel of varying length. Known tarsal setation I–V, respectively: (19–22)-(16)-(15–16)-(12–13), tarsal solenidia 2-2(1)-0-0; genu I and tibia IV each with a single solenidion; tibia I with 2 solenidia borne on a strong distal apophysis; femur I with 5 setae; femur IV with a maximum of 3 setae; trochanter IV with 0–1 seta; legs I and IV may approach the length of body. Subcapitulum diarthric, lateral lip with 2 setae, gena with 2 pairs of setae (a, m), mentum with one pair of setae and base usually covered by well developed mentotectum; epimeral setation 3-1-3-3; ventral plate may have pair of deep, funnel-shaped pits laterally near insertion of legs IV; anal and genital openings separated by band of the ventral plate (ano-genital bridge) that covers the preanal organ or confluent with a narrow band of soft cuticle between the plates, in which case preanal organ appears to be hinged to spur- processes of the ventral plate; anal plates each with 2 setae; genital plates each with 6–7 setae, g 2 inserted posteriad or laterad g 1.

Immatures. Multideficient, dorso-central setae present only in the larva, nymphs with a maximum of 9–10 pairs of gastronotal setae (c 1-3, h 1-3, p 1-3, +/- lp) displaced to margin of gastronotum, more or less plicate cuticle and bearing stacked remnants of previous dorsal notogastral exuviae (eupheredermous) ( Fig. 26 ).

Comments: The immature stages of Gymnodamaeidae are poorly known. For example, Grandjean (1954b) studied only Arthrodamaeus reticulatus (Berlese) for his classification of oribatid mites and only a few other studies (e.g. Perez-Iñigo 1997, Bayartogtokh & Schatz 2009) address the characters in immatures. Given the presence of 10 pairs of gastronotal setae in the tritonymph of Gymnodamaeus meyeri Bayartogtokh & Schatz , it is not clear if adult gymnodamaeids with 6 pairs of notogastral setae retain seta h 3 or lp, but the assumption of h 3 is made here. Additionally, the leg chaetotaxy as sparsely summarized here for the family must be considered preliminary.

Figures

FIGURES 22 – 31. J oshuella agrosticula Paschoal, 1983, Alberta, Canada. 22, Dorsal view (arrow points to longitudinal notogastral ridge), scale bar = 0.05 mm; 23, Ventral view (arrow points to anogenital bridge), scale bar = 0.05 mm; 24, Posterior notogaster showing 4 pairs of setae, scale bar = 10 μm; 25, Notogastral pustules, scale bar = 1 μm; 26, Tritonymph with stacked scalps, scale bar = 0.05 mm. Pleodamaeus plokosus (Woolley & Higgins, 1973), South Dakota, USA. 27, Dorsal habitus, scale bar = 0.1 mm; 28, Notogastral pustule, scale bar = 1 μm; 29, Tubercular patch (arrow) on median anterior rim of notogaster, scale bar = 10 μm; 30, Light micrograph showing tubercular patch and median prodorsal tubercle. Pleodamaeus sp., Alberta, Canada. 31, Anterior notogaster and prodorsum showing acuminate pedotectum II (arrow), scale bar = 0.05 mm.