Diagnosis

Adults of medium size (332–377), with characters of ‘rugosus group’ of Limnozetes. Lamella narrow, with well developed cusp, translamella incomplete. Seta in not reaching incomplete translamella, bothridial seta short, setiform, barbed. Notogaster convex (body length to height ratio 1.9:1), with elongated and rounded microtubercles, short and thin setae, length to width ratio of notogaster and length to width ratio of pteromorph 1.2:1 and 1.4:1, respectively. Genal tooth triangular, acuminate, with more sharpened distal part than in L. solhoyorum. Seta d on femora I–III and seta l′ on femora I and II with relatively long barbs, covered often with debris. Seta l′ on femur III absent.

Juveniles with plicate cuticle, and other characters of ‘rugosus group’ of Limnozetes. Prodorsal setae le and in and bothridial seta long and thin, gastronotal setae short and thin. In tritonymph, seta l″ on femora I and II, l′ on femur III absent.

Adult. Measurements: body length (and range): females 348.4±12.1 (332–377, n= 50) and width 215.5±9.3 (202–234), males absent.

Prodorsum. Rostrum dorsally rounded, but with two indentations in frontal aspect, lamella long, translamella incomplete, lamellar cusp of medium size (16), rounded, with lamellar seta of medium size (Figs. 1a, 2, 3a, 4, 5, Table 1). Setae le and in longer (45–48) than ro (30–32), and in thinner than le and ro, seta ex short; in with short barbs, other setae smooth. Seta ro inserted on lateral part of rostrum, seta in inserted close to inner border of lamella and anterior border of notogaster. Bothridium rounded, with well developed dorsal expansion (Figs. 1a, 3a, 6a, 6b), bothridial seta short (11–12), setiform, barbed. Medial and posterior parts of prodorsum irregularly tuberculate (Figs. 5b, 5c).

Notogaster. Convex (body length to height ratio 1.9:1), length to width of notogaster (Figs. 1a, 4a) and length to width of pteromorph (Figs. 3a, 4c) is 1.2:1 and 1.4:1, respectively. Ten pairs of notogastral setae present, including c₂, all thin and short (Figs. 1a, 3a, 4, 5b, 5c, 6c, Table 1), seta h₃ inserted closer to h₂ than to lp. Notogaster with elongated and rounded microtubercles (Figs. 1a, 5b, 5c, 6c). Lyrifissures ia and im posterolateral to seta c₂ and posterior to seta la, respectively, ip anterolateral to seta h₁, ips and ih anterolateral and medial to seta p₃, respectively, and iad anteromedial to seta ad₃ (Figs. 1a, 2, 3a).

Gnathosoma. Subcapitular seta h, m and a short (8–10) and smooth (Fig. 2). Chelicera (length 97–99, width 37) with short setae (12), cha thicker than chb and barbed, chb smooth (Fig. 3c). Palp short (length 66–68) with short and smooth setae (Fig. 3d), except for slightly barbed seta l″ on tibia, palpal eupathidium acm fused with solenidion ω, eupathidia ul₁, ul₂ and su short. Formula of palp setae (trochanter to tarsus + solenidion ω): 0-2-1-3-9(1).

Lateral aspect. Pedotectum I large, oval, covering basal part of leg I, pedotectum II small, circumpedal carina incomplete, porose area Ah elongated, difficult to observe.

Ventral aspect. All epimeral setae short and smooth (Figs. 2, 4d), formula of epimeral setae 3-1-2-2. Genital setae (6 pairs) smooth and inserted on inner part of genital plates (Figs. 2, 6d). One pair of aggenital setae, three pairs of adanal and two pairs of anal setae; all short. Ventral and anal plate with small microtubercles (Figs. 4d, 6d).

Legs. Seta d on femora I–III and seta l′ on femora I and II with relatively long barbs (Figs. 1a, 3a, 5b, 5c, 6b, 7), and some parts of them often with debris. Seta l″ on genua I and II thicker than other leg setae, famulus ε on tarsus I close to solenidia ω₁ and ω₂, but hardly visible in light microscope, solenidia ω₁ and ω₂ on tarsi I and II glued at some distance from insertions, seta l′ absent from femur III, distal setae on all tarsi short, thick and barbed, setae d and l′ on genu IV absent. Formulae of leg setae [trochanter to tarsus (+ solenidia)]: I—1-4-3(1)-4(2)-15(2); II—1-4-3(1)-4(1)-14(2); III—2-2-1(1)-3(1)-13; IV—1-2-0-3(1)-10. Tarsi heterotridactylous.

Juvenile stages

Larva oval in dorsal aspect, light brown, cuticle plicate (Figs. 8, 9, 11a). Prodorsum subtriangular, setae le and in long and with short barbs, seta ro of medium size and seta ex short, both smooth (Table 1). Mutual distance between setal pair le about two times longer that between setal pair ro, and mutual distance between setal pair in about six times longer that between pair ro. Pair le inserted closer to pair ro than to pair in. Opening of bothridium small, oval, bothridial seta setiform and smooth, and about twice longer than seta in. Area between bothridia with transverse folds, lateral parts with longitudinal folds.

Gastronotum of larva with 12 pairs of setae, including minute h₃ inserted laterally to medial part of anal valves (Figs. 10a, 11a). All gastronotal setae short and smooth (8, 9, 10a, 11a, Table 1). Cupules not observed in plicate cuticle. Opisthonotal gland opening posterolateral to seta lm (Fig. 11a). Paraproctal valves (segment PS) glabrous. Most leg setae short, conical and smooth, distal setae on all tarsi short, thick and barbed (Fig. 12).

Prodorsum of protonymph porose, prodorsal setae and bothridial seta as in larva. Gastronotum of protonymph with 15 pairs of setae because setae of p-series appearing (Fig. 10b), and present in subsequent nymphs (Figs. 13a, 13b); all short and smooth. In protonymph, one pair of genital setae present on genital valves, and two pairs added in deutonymph and two pairs in tritonymph, all short and smooth. In deutonymph, one pair of aggenital setae and three pairs of adanal setae added, and retained in tritonymph (Figs. 13a, 13b), all short and smooth. In protonymph and deutonymph, anal valves glabrous, in tritonymph two pairs of short and smooth anal setae present. In all nymphs, cupules not observed in plicate cuticle, opisthonotal gland opening anterolateral to seta lp (Fig. 11b). Some gastronotal setae hardly visible in plicate cuticle in light microsopy, but better observed in SEM micrographs (Figs. 15, 16a). Leg segments of tritonymph stocky, most leg setae short and conical (Figs. 16c, 16d, 17), famulus ε on tarsus I hardly visible in light microsopy, solenidia ω₁ and ω₂ on tarsi I and II glued together at some distance from insertions; seta l″ on femora I and II, l′ on femur III absent.

Summary of ontogenetic transformations

In all juveniles of L. schatzi, setae le and in are long, ro is of medium size and ex is short, whereas in the adult in remains long, ro and le are of medium size, and ex is short. The bothridium is small and rounded in all juveniles, but in the adult, it is larger, and develops a dorsal scale. In all juveniles, the bothridial seta is long, setiform, whereas in adults it is short and setiform, barbed. In all instars, the gastronotal setae are short. The larva has 12 pairs of gastronotal setae, including minute h₃, the nymphs have 15 pairs (p-series is added). The notogaster of adult loses setae c₁, c₃ and of d-series, such that 10 pairs of setae remain. The formula of gastronotal setae of L. schatzi is 12-15-15-15-10 (from larva to adult), formulae of epimeral setae is 2-1-2 (larva), 3-1-2-1 (protonymph), 3-1-2-2 (deutonymph, tritonymph and adult), formula of genital setae is 1-3-5-6 (protonymph to adult) and formula of aggenital setae is 1-1-1 (deutonymph to adult). Fomula of segments PS–AN is 03333-0333-022. The ontogeny of leg setae and solenidia of L. schatzi is given in Table 2.

Distribution, ecology, and biology

We found quite a large population of L. schatzi in Høstedmyra (Trøndelag, Central Norway), in a hollow filled with water and overgrown by Sphagnum compactum. In one sample of this peat moss 14 oribatid species were found and the total density of Oribatida was 1722 specimens per 500 cm³. The most abundant oribatid species was L. ciliatus which comprised 43.0% of all specimens collected. The second abundant species was Trhypochthoniellus longisetus (Berlese, 1904, in Berlese 1905) which comprised 12.2% of Oribatida, followed by L. foveolatus (12.0%) and L. schatzi (11.4%). The density of L. schatzi was 197 specimens per 500 cm³ of peat moss. In the sample population, the adults dominated (71% of all individuals), and the stage structure was: 3 larvae, 16 protonymphs, 34 deutonymphs, 4 tritonymphs and 140 adults. Only females were noted, and 70% of them were gravid, carrying one or two large eggs. The eggs were relatively large (175 x 80), comprising 50% of total body length of females.

Type material

The holotype (female) and five paratypes (females) with above collection data are deposited in University Museum of Bergen, University of Bergen, Bergen, Norway.

Etymology

This species is named in honour of Dr. Heinrich Schatz (c/o Institute of Zoology, University of Innsbruck, Austria), who is an outstanding oribatologist and very helpful and appreciated Colleague.

Comparison of the morphology of Limnozetes schatzi with congeners and remarks

The adult of L. schatzi sp. nov. is the largest species of ‘rugosus group’ of Limnozetes, while the smallest are L. guyi and L. latilamellatus, but the body length of all species overlaps (324–377, Table 3). None of species has a complete translamella, but in some species, including L. schatzi, the translamella is incomplete. The stockiest species is L. latilamellatus, and the slimmest is L. rugosus. In in all species the bothridial seta is setiform, but in L. schatzi and L. borealis it is barbed, while in other species it is smooth. In most species, setae ad-series are short, but in L. borealis and L. latilamellatus they are of medium size. In both species, anal and aggenital setae are also medium sized, as are epimeral setae in L. borealis. These species differ also from one another by the location of seta h₃ on the notogaster, length of some setae on the main body and length and presence of some setae on legs (Table 3). Seniczak and Seniczak (2020) compared the morphology of all species of Limnozetes, and the adults of ‘rugosus group’ differ from’ciliatus group’ mainly by more convex notogaster and lack of setae d and l′ on genu IV, which are present in the ‘ciliatus group’.

The adult of L. schatzi is the most similar to that of L. rugosus, including rostral structure, but differs from it mainly by the shape of body (stockier in dorsal aspect, and less convex in lateral aspect than L. rugosus), longer prodorsal seta in and notogastral setae, lack of seta c₃, which in some individuals of L. rugosus is present, and sculpture of notogaster (Seniczak & Seniczak 2020). For example, in SEM micrographs, the anterior part of notogaster of both species has elongated elevations, but in L. schatzi these elevations are longer than in L. rugosus. Moreover, L. schatzi has seta d on femora I–III and seta l′ on femora I and II with longer barbs than L. rugosus (best observed in dorsal aspect), lacks seta l′ on femur III, which in L. rugosus is present, and has seta ev on femur IV shorter than on femur III, whereas in L. rugosus this seta is of similar length (Seniczak & Seniczak 2020). In the juveniles of L. schatzi, the gastronotal setae are short, whereas in those of L. rugosus lm and lp in larva, lp in nymphs are longer. Moreover, in L. schatzi seta l′ on femur III is absent, but in L. rugosus is present (Table 4).

Grandjean (1951), Behan-Pelletier (1989) and Seniczak and Seniczak (2020) compared several morphological characters of Limnozetes and Hydrozetes Berlese, 1902 and stated that these genera are closely related, that was also supported by the molecular phylogeny (Krause et al. 2016). The ontogeny of leg setae of Limnozetes species differs from that of Hydrozetes species, but in both genera the tarsal setae u and p are short, thick, and barbed (Seniczak & Seniczak 2008, 2009a, 2009b, 2010; Seniczak et al. 2007, 2009, 2017), reflecting their ecological importance. They cooperate with claws and help the mites to stick to water plants, which can be easily observed while manipulating mites with the needle.

Our study on L. schatzi shows the importance of SEM micrographs for better understanding the morphology of this species. For example, the sculpture of some parts of body of the adult of L. schatzi illustrated from light microscopy does not fully reflect the SEM micrographs, which better characterize the difference between species. The famulus ε on tarsus I is difficult to observe in a light microscopy and is well observed in SEM micrographs, similarly as the shape of palp setae and solenidion (Seniczak & Seniczak 2020).