Gymnodamaeus bicostatus

Weigmann, G. & Mourek, J., 2008, Contribution to the Central European Gymnodamaeus species G. barbarossa and G. bicostatus (Acari, Oribatida, Gymnodamaeidae, Zoosystematics and Evolution 84, pp. 255-264 : 260-263

Characteristics of Gymnodamaeus bicostatus (C. L. Koch, 1835)

Figures 5, 6d, 7b-c

Damaeus bicostatus C. L. Koch, 1835: CMA 2.12.

Gymnodamaeus bicostatus : Kulczynski 1902, Grandjean 1954, Ghilarov & Krivolutsky 1975, Paschoal 1982, Woas 1992, Perez-Inigo 1997, Weigmann 2006.

Eremaeus asperulus Berlese, 1882: syn. after Mahunka & Mahunka-Papp 2004.

Recently, G. bicostatus was redescribed by Perez-Inigo (1997) and in detail by Woas (1992). In this paper we therefore restrict the comments to differences from G. barbarossa and to some new details of the cerotegument. We also studied complete leg setation, because Woas (1992) gave setal formulas for leg I and IV only.

Specific characters. Body length 636-756 µm (for details see Table 1); posterior submarginal notogastral setae h1 and h2 different, h1 about 20 µm, h2 about 50 µm in length; posterior notogastral setae p1-p3 situated on the ventral boarder of notogaster, about 8-12 µm in length; notogaster at the posterior edge without double- indentation; sensilli with long stalk, head slender, flattened-fusiform with fine spines, length up to 200 µm; interlamellar setae very small and stout, positioned on projecting apophyses at the medio-anterior edge of the interlamellar costulae. The ornamentation of the more or less opaque cerotegument mass at the centre of the notogaster forming namely two parallel length-ridges with a transversal connection at the posterior end (fig. 5a) and often with two pairs of short projections directed laterad. The normal cerotegument layer consisting of a thin cuticular cover with some irregular lines, but without a mesh net formed by microgranula; the large cerotegument granula on the body surface and on proximal segments of the legs of about 2,5 µm diameter with a semi-globular form and covered only at the lateral parts with a dense mesh-net pattern formed by micro-granula, tops of the granula smooth or covered with several irregular microgranula (granula on prodorsum: see figure 5c, granula on genu: see figure 7c). On tarsi of legs with different cerotegument granula, similar to those of G. barbarossa (see figure 7b). Legs relatively longer than in G. barbarossa , leg IV at least as long or longer than body (see Table 1); leg IV> leg I> leg III> leg II. Setal formulas of the legs as follows, identical with that of G. barbarossa (from trochanter to tarsus, famulus included solenidia in parentheses, claws not included): I: 1-5-4(1)-5(2)-20(2); II: 1-4-4(1)-5(1)- 16(2); III: 2-3-3(1)-4(1)-15; IV 1-2 -3-4(1)-12.

Material examined

Austria: Obergoldes south of Graz , leg. R. Schuster 2001; in thick litter layer, mixed forest with Fagus , Castanea and others (specimens for microscopical studies in Weigmann 2006). - Austria, Virgental , Central Alps, leg. H. Schatz 1993, dry meadow, partly in litter of Juniperus shrubs (Schatz 1995). - Germany: Berlin , leg. H. Woltemade 1978; litter of Quercus trees, at a roadside of a forest area. The material from Austria and Germany was deposited in coll. G. Weigmann (Berlin). - Czech Republic: Southeast Moravia, northeast from the Pouzdrany village, Pouzdranska step National Reserve (48° 57 ’ N, 16°39 ’ E, altitude about 390 m), warm grassland with groups of Staphylea pinnata , Prunus domestica , Acer campestre and Quercus pubescens on loess soil, top of the hill and eastern slope, 16.09.2006 J. Mourek leg., (11 specimens in alcohol, 6 specimens mounted for SEM study) ; 17.05.2007 J. Mourek leg., (7 specimens in alcohol) , coll. J. Mourek - Slovakia: South Slovakia, Kovacovske kopce, about 3 km east of Kamenica nad Hronom (47°50'N, 18°38'47''E), forest steppe south-exposed slope near the top of the hill, 24.06.2004 F. St'áhlavský leg. (18 specimens in alcohol, 2 specimens mounted for SEM study) , the material from the Czech Republic and Slovakia deposited in coll. J. Mourek.

Distribution. Holarctic: in several countries of Europe and Asia; North Africa; North America (Marshall et al. 1987).

Ecology. Rajski (1967) discussed the controversial ecological preferences; in Southern Europe the species is more or less xerophilous and thermophilous (cf. Schatz 1983); for Eastern Austria Schuster (1960) indicated the preference for “ moderately dry and moderately fresh habitats ”. In temperate and northern climatic conditions in the Palaearctic the species occurs predominantly in litter layer of mesohygric forest soils (cf. in Poland: Rajski 1967, Woas 1992; in Berlin, Germany: Woltemade 1982).

New findings in dry and warm forest areas in Germany (Horak et al. 1997; Russell et al. 1994; Kratzmann etal. 1993) support the thermophilous predominance of the species also for Central Europe. Remarkably, Strenzke (1952) found it in dry moss on a roof in Northern Germany. But there are northern Palaearctic and subalpine records, referred e.g. in Rajski (1967) and Schatz (1983), which indicate a broader temperature tolerance.

Comparative remarks

G. bicostatus (C. L. Koch, 1835) is the first species of Gymnodamaeidae , described in “ Deutschlands Crustaceen, Myriapoden und Arachniden ” vol. 2 (not published in 1836, as indicated by several authors) as Damaeus bicostatus , and it is the type species of Gymnodamaeus Kulczynski, 1902. There are about 20 species of the genus Gymnodamaeus s. str. (cf. Subías 2004), the taxonomical positions of some species are questionable, some with uncertain synonymy. The taxonomical conception is controversial, e.g. comparing that of Woas (1992) versus Parschoal (1982; Paschoal & Johnston 1982) but is not object of this paper. This contribution focuses on European species of Gymnodamaeus s. str. The Spanish species G. quadriseta Ruiz, Kahwash and Subías, 1990, is similar to G. bicostatus in regard of prodorsal characters (sensillus shape, insertion of interlamellar setae) but differs mainly in smaller body size (460-510 µm) and in reduced numbers of notogastral setae (only two pairs at the posterior margin).

Comparing the microstructure of the cerotegument granula in G. bicostatus and G. barbarossa , the granula of the body cerotegument are significantly different (Figs 5c, 6b,e), but not on distal segments of the legs (Figs 7a-c). Cerotegument granula similar to those of G. barbarossa can be found on the tarsi of legs of G. bicostatus , also. At the first sight, the cerotegument granula of G. bicostatus seem, that they are somehow abraded on their tops, but it was stable among the studied specimens from different localities. Already Woolley (1972, 1973) presented SEM micrographs of cerotegument granula in G. chalazionus Woolley, 1972; in principle, the granula are structured as those in the European species, in detail they are different on the notogaster and ventral plate of G. chalazionus , and both are not identical to those in G. bicostatus and G. barbarossa . The cerotegument granula are not studied in most Gymnodamaeus species, and therefore the taxonomy may use this character additionally, only.