Gymnodamaeus Kulczynski, 1902

Walter, David Evans, 2009, Genera of Gymnodamaeidae (Acari: Oribatida: Plateremaeoidea) of Canada, with notes on some nomenclatorial problems, Zootaxa 2206, pp. 23-44 : 26-27

Gymnodamaeus Kulczynski, 1902

Heterodamaeus Ewing, 1917

Type species: Damaeus bicostatus C.L. Koch, 1835

Diagnosis: Gymnodamaeidae with a ventral plate typically lacking an anogenital bridge ( Figs. 4, 7 , arrows), but with lateral pits; genital plates with smooth median margin and bearing 7 pairs of setae, seta g 2 inserted posteriad g 1; 2 pairs of adanal setae. Legs without retrotecta on distal segments ( Fig. 8 ), femur IV with 2 setae. Prodorsum without X-shaped raised cerotegumental ridges ( Figs. 1–2, 5–6 ), with spherical pustules ( Fig. 3 ); sensillus (bo) with long stalk and elongate, barbed head ( Fig. 2 ); bothridial rim simple, bothridial ridges well developed, arising anteriad bothridia, and ending in strong apophyses bearing the spine-like interlamellar seta (in) and forming enantiophysis with median prodorsal tubercle ( Figs. 1 arrow, 2); exobothridial seta (ex) inserted posteriad in; rostral seta (ro) inserted posteriad lamellar seta; lamellar seta (le) curves ventrad, inserted at anterior base of strong transverse prelamellar ridge ( Figs. 1–2, 6 ); pedotectum II rounded distally. Notogaster flattened, with 5 pairs of more or less sessile setae (h 1-2, p 1-3), raised rim, crenulate outer margin, and posterior median nipple-like process between setae h 1; without anterior median tubercular patch; cerotegument with spherical pustules and usually with a pattern of raised ridges or cells and parallel marginal folds ( Fig. 5 ); sejugal tubercle well developed.

Comments: As discussed in Woas (1992), the actual identity of the type species G. bicostatus is contentious: the location of the holotype is unknown ( Marshall et al. 1987) and two similar forms that vary in the presence (e.g. Willmann 1931, Woas 1992) or absence (e.g. Grandjean 1954a, Paschoal 1982a, Weigmann 2006) of a narrow anogenital bridge are known. Woas (1992) argued that although it may represent intraspecific variation, the form with a narrow anogenital bridge is likely to be the true G. bicostatus because it is present in Poland near the site of its presumed type locality. Gymnodamaeus bicostatus has been shown with a smooth notogaster (e.g. Paschoal 1982a), but it actually has a U-shaped cerotegumental ridge with outer branches formed from certotegument (e.g. Woas 1992, Weigmann 2006, Weigmann & Mourek 2008). In slide-flattened specimens these ridges can be difficult to observe (and are absent or obscure in recently moulted individuals).

About a dozen species of Gymnodamaeus are known from North America, but according to Paschoal (1982a) G. bicostatus does not occur in North America and, except as quarantine interceptions (e.g. Hammer 1969), previous records refer to other species. For example, the record of G. bicostatus in Alberta on the Diversity of Oribatida in Canada website ( Behan-Pelletier & Eamer 2004) is based on the Powell & Skaley (1975) study listed in Marshall et al. (1987), but Paschoal (1982a) must have considered this a misidentification, since the specimen was designated as the holotype of Gymnodamaeus taedaceus Paschoal.

With the exception of three Paschoal species (see below), and one record for G. sp. nr. bicostatus ( Oswald & Minty 1971) , other Canadian records for Gymnodamaeus have been attributed to G. ornatus Hammer, 1952 . Hammer (1952) described this species from Reindeer Station based on 7 specimens of which I have observed two syntypes on a slide in the CNC. She distinguished G. o r n a t u s from G. bicostatus by the smooth ridges forming “oval and crescent-shaped areas” (p. 28) on the notogaster and by the longer lamellar setae that project beyond the tip of the rostrum. Length of the lamellar seta, however, is difficult to judge from a dorsal slide mount (compare Fig. 2 to 6). Also, her illustration (fig. 35, p. 98) shows a more elaborate cell pattern on the notogaster than I usually find on Canadian specimens. The syntypes are flattened, but as far as can be discerned show the more typical form having one central U-shaped cell with incomplete internal ridges and two pairs of arms forming partial (rarely complete) lateral cells. The oval and crescentic areas within the Ushaped ridges appear to be artefacts caused by smooth areas without pustules and not by raised ridges; complete lateral cells are not visible on the syntypes, but I have seen a few specimens with one present asymmetrically.

Gymnodamaeus ornatus and G. bicostatus are very similar (see Weigmann & Mourek 2008) and may be conspecific. Since this problem cannot be resolved at this time, I accept Woas’ (1992) diagnosis of G.

bicostatus as having a narrow anogenital bridge and refer the very similar mite that lacks the anogenital bridge to G. cf. ornatus Hammer, 1952 . I have cox1 mitochondrial DNA sequences of the barcode region for 4 specimens from an Alberta population of G. cf. ornatus and they may be informative if comparisons can be made to European populations of G. bicostatus .

The holotype slides and only known specimens of G. saltuensis Paschoal and G. taedaceus were located in the CNC: both were labelled “ Gymnodamaeus bicostatus (Koch) ” but were identified by the collection data recorded in Paschoal 1975 and 1982a. Both mites were badly crushed, perhaps the reason that no illustrations were provided for the species ( Paschoal 1975, 1982a). Powell & Skaley (1975) published the “ Gymnodamaeus bicostatus (Koch) ” record in a pine blister rust study in Alberta which was subsequently used by Marshall et al. (1987) and Behan-Pelletier & Eamer (2004) to report this European species in Canada. I consider these species to be species inquirenda for the following reasons: the types, and only known specimens, of these two species are both badly crushed; one is a male and one a female; most of the major characters in the descriptions were misinterpretations of thick areas of cuticle (mostly ridges or tubercles on the surface of the mite) as apodemata; many other characters call for qualitative judgements; and there is no way to distinguish the descriptions of these mites from each other or from G. ornatus . Bayartogtokh & Schatz (2009) similarly considered these species to be unrecognizable, and suggested that they should be treated as a species inquirendae.

Gymnodamaeus victoriae Paschoal can be identified, but is transferred to Roynortonella below. Types of Gymnodamaeus gregarious Paschoal and G. orbicularis Paschoal are in good condition, and clearly members of Gymnodamaeus .

Figures

FIGURES 1 – 8. Gymnodamaeus cf. ornatus Hammer, Alberta, Canada; scale bars = 0.1 mm, except Fig. 3 = 1 μm. 1, Prodorsum showing interlamellar seta (in) on apophysis at median edge of bothridial ridge and opposed to median prodorsal tubercle (larger arrow); 2, Prodorsum and anterior notogaster; 3, Spherical crystalline notogastral pustules; 4, Ano-genital region, arrow points to soft cuticle between genital and anal openings; 5, Dorsal habitus view showing Ushaped raised notogastral ridge pattern; 6, Rostrum from anterior view; 7, Light micrograph of ano-genital region, arrow points to preanal organ; 8, Genu IV (DIC micrograph) showing normal joint, i. e. lacking retrotecta, between femur (top) and tibia.