Diagnosis

Adults of medium size (344–364), with characters of Limnozetes. Lamella narrow, with well developed cusp, translamella absent. Seta in reaching half length of lamella, sensillus short, setiform. Notogaster convex, with elongated and rounded foveae, short and thin setae, length to width of notogaster and length to width of pteromorph similar (1.2:1). Famulus on tarsus I present, but setae d and l' from genu IV absent.

Juveniles plicate, with characters of Limnozetes. Prodorsal setae le and in and bothridial seta long and thin, whereas gastronotal setae short and thin, except slightly longer lp, h₁ and h₂ in larva, and p₁ and h-series in nymphs. In deutonymph and tritonymph, setae d and l' from genu IV absent.

Adult. Measurements: mean body length (and range): females 353.9 (344–364, n= 50) and width 240.1 (234–244).

Prodorsum. Rostrum rounded, lamella long, without translamella, lamellar cusp of medium size (14), rounded, with lamelar seta (Figs. 1a, 2, 3a, 4a, 4b, 4c, 5a, Table 1). Setae le and in longer (46–48) than ro (33–35), and in thinner than le and ro. Seta ro inserted on lateral part of rostrum, whereas seta in inserted close to inner border of lamella and anterior border of notogaster. Bothridium rounded, with well developed dorsal expansion (Figs. 1a, 5a), bothridial seta short, setiform. Medial and posterior parts of prodorsum punctate.

Notogaster. Convex, ratio length to width of notogaster similar to ratio length to width of pteromorph (1.2:1, Figs. 4a, 5c). Ten pairs of notogastral setae present, including c₂, all short (Table 1) and thin. Notogaster with elongated and rounded foveae, anterior part and pteromorphs with more elongated foveae than central part (Figs. 1–3a, 4, 5a). Lyrifissures ia and im posterolateral to seta c₂ and posterior to seta la, respectively, ip posterolateral to seta h₁, ips and ih anterior and anteromedial to seta p₃, respectively, and iad anteromedial to seta ad₃ (Figs. 1a, 2, 3a).

Gnathosoma. Subcapitular seta h as long as m (23), seta a slightly shorter (16), all smooth (Figs. 2, 5b). Chelicera (length 87–89, width 38) with setae of similar length (12), cha thicker than chb, both barbed (Fig. 3b). Palp (length 55–57) with short and smooth setae (Figs. 3c, 5b, 6b, 6d), palpal eupathidium acm fused with solenidion ω at some distance from insertion of solenidion, eupathidia ul₁, ul₂ and su short (Figs. 3c, 6b, 6d). Formula of palp setae (trochanter to tarsus + solenidion ω): 0-2-1-3-9(1).

Ventral aspect. All epimeral setae short and smooth (Figs. 2, 4d), formula of epimeral setae 3-1-2-2. Six pairs of genital setae, all short and smooth, inserted on inner part of genital plates. One pair of aggenital setae as short as genital setae. Anadal setae short, but slightly longer than anal setae. Ventral and anal plate with elongated and rounded foveae (Figs. 4d, 5c).

Legs. Seta d on femora I–III very long, curved and barbed (Fig. 7). Seta l'' on genua I and II relatively thick, famulus ε on tarsus I short, solenidia ω₁ and ω₂ on tarsi I and II fused at some distance from insertions (Figs. 6a, 7a, 7b, 7e), setae d and l' absent from genu IV, distal setae on tarsi short, thick and barbed (Fig. 6c, 7). 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—2-3-1(1)-3(1)-13; IV—1-2-0-3(1)-10. Tarsi heterotridactylous.

Juvenile stages

Larva oval in dorsal aspect, light brown, cuticle plicate (Fig. 8). Prodorsum subtriangular, all prodorsal setae thin and smooth; ro of medium size, le and in long and ex short. Mutual distance between setal pair le about two times longer than between setal pair ro, and mutual distance between setal pair in about four times longer than between pair ro. Pair le inserted closer to pair ro than to pair in. Opening of bothridium small, oval, bothridial seta setiform and longer than seta in. Area between bothridia with transverse folds, lateral parts with longitudinal folds.

Gastronotum of larva with 12 pairs of setae, including h₃ inserted laterally to medial part of anal valves (Figs. 9a, 10a). Setae of c-series and h₃ minute, other gastronotal setae short, but posterior setae, especially seta lp, longer than other setae (Fig. 8, 10a, Table 1), all smooth. Cupules not observed in plicate cuticle. Opisthonotal gland opening anterolateral to lp (Fig. 10a). Paraproctal valves (segment PS) glabrous. Most leg setae short, setae l' and l'' on all genua and tibiae thicker than v' on tibiae (Fig. 11).

Prodorsum of protonymph porose, prodorsal setae and bothridial seta as in larva. Gastronotum of protonymph with 15 pairs of setae due to appearance of setae of p-series (Fig. 9b), retained in subsequent stages (Figs. 12a, 12b); all short and smooth. In protonymph, one pair of genital setae present on genital valves, and two pairs added in deutonymph and tritonymph each, all short and smooth. In deutonymph, one pair of aggenital setae and three pairs of adanal setae added, and retained in tritonymph (Figs. 12a, 12b), all short and smooth. In protonymph and deutonymph, anal valves glabrous, in tritonymph two pairs of short and smooth anal setae present. Cupules not observed in plicate cuticle, opisthonotal gland opening anterolateral to seta lp (Fig. 10b). Some anterior and medial setae hardly visible in plicate cuticle, posterior marginal setae on gastronotum longer than other setae (Figs. 10b, 12a, 12b, 13, 14, 15a). Palp of tritonymph with short and smooth setae, palpal eupathidium acm fused with solenidion ω at some distance from insertion, eupathidia ul₁, ul₂ and su short (Figs. 15c, 15d). Leg segments stocky, most leg setae short, setae l' and l'' on genua I and II and tibiae I and II thicker than seta v' on tibiae I and II (Fig. 16a, 16b). Famulus ε on tarsus I short, solenidia ω₁ and ω₂ on tarsi I and II fused together at some distance from insertions (Figs. 16a, 16b, 16e, 17a, 17b). In tritonymph, seta l'' on femora I–III present or absent, and setae d and l' from genu IV absent (Fig. 16).

Summary of ontogenetic transformations

In all juveniles of L. solhoyorum, setae le and in are long, ro is of medium size and ex is short, whereas in the adult in, le and ro are long, and ex is short. The bothridium is small and rounded in all juveniles, but in the adult it gets larger, and develops a dorsal expansion. In all juveniles, the bothridial seta is long, setiform, whereas in adults it is short, setiform or absent. In all instars, the gastronotal setae are short. The larva has 12 pairs of gastronotal setae, including 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, all are short and smooth. The formula of gastronotal setae of L. solhoyorum is 12-15-15-15-10 (from larva to adult), formulae of epimeral setae are 2-1-2 (larva), 3-1-2-1 (protonymph) and 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. solhoyorum is given in Table 2.

Distribution, ecology and biology

We found a large population of L. solhoyorum sp. nov. in a small pool in submerged moss Warnstorfia fluitans. In this pool, 5,994 individuals of L. solhoyorum were collected in 2 dm³ of moss, corresponding to density 150,000 individuals per m². This species constituted 82% of all Oribatida, being accompanied by Hydrozetes octosetosus Willmann, 1932a (17% of Oribatida) and single individuals of Hydrozetes lacustris (Michael 1882), Limnozetes foveolatus Willmann, 1939, Tyrphonothrus maior (Berlese 1910), Oppiella nova (Oudemans 1902) and Diapterobates humeralis (Hermann 1804). Juveniles of L. solhoyorum constituted 24% of all individuals of this species and the stage structure was: 119 larvae, 539 protonymphs, 732 deutonymphs, 50 tritonymphs and 4,554 adults. In the same bog, one adult of L. solhoyorum was also found in Sphagnum pulchrum (Lindb. ex Braithw.) Warnst and two adult individuals were found in S. riparium Ångstr. (mentioned as Limnozetes. sp. 1 in Seniczak et al. 2019b). Only females were noted, and 70% of them were gravid, carrying one or two large eggs. The eggs were relatively large (157 × 94), comprising 44% 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 two oribatologists working in Norway: Dr. Ingrid Wunderle-Solhøy and Prof. Torstein Solhøy, University of Bergen.

Comparison of the morphology of Limnozetes solhoyorum with congeners

Limnozetes Hull, 1916, with the type species L. ciliatus, comprises medium sized mites as adults (266–390 µm), with Limnozetes characters. Subías (2019) listed 14 species in Limnozetes, including Limnozetes palmerae Behan-Pelletier, 1989, but the latter species we consider a junior synonym of L. foveolatus Willmann, 1939, as suggested by Siepel et al. (2009) and supported by Lehmitz et al. (2019). Among these species, the largest is L. similis Pérez-Íñigo & Baggio, 1989 and the smallest is L. foveolatus. The body length of most species overlaps (Table 3). These 14 species also differ one from another by the presence of translamella, shape of bothridial seta, shape of notogaster and pteromorph, length of some setae and presence of setae d and l' on genu IV.

Based on the ontogeny of leg setae (Table 2), setae d and l' are also absent from genu IV in deutonymphs and tritonymphs of the ‘rugosus group’ (L. borealis, L. guyi, L. latilamellatus, L. rugosus, L. solhoyorum sp. nov.), with plicate cuticle (Behan-Pelletier 1989; Seniczak & Seniczak 2010), whereas these nymphs of the'ciliatus group', with boat-shaped juveniles, have these setae. Among the adults of the ‘rugosus group’, with plicate juveniles, L. borealis and L. rugosus have an incomplete translamella, whereas other species lack the translamella. However, in L. latilamellatus the lamella is wide, without lamellar cusp, which is unique in Limnozetes, whereas in L. solhoyorum and L. guyi the lamella is narrow, with lamellar cusp. From this comparison it is evident that L. solhoyorum is most similar to L. guyi, but differs from it mainly by shorter prodorsal seta in and notogastral setae, especially p₁, and by the distribution of posterior setae on the notogaster. In L. solhoyorum, seta h₁ is inserted more medially than in L. guyi (Behan-Pelletier 1989). The tritonymph of L. solhoyorum differs from that of L. guyi mainly by shorter gastronotal seta c₃, dm, dp, lm and lp. The body size of the adult of L. solhoyorum overlaps with that of L. rugosus, and the shape of body, pteromorph, leg setae, solenidia and famulus ε is also similar in both species (Figs. 4, 5a, 5c, 6a, 7, 18, 19, 20). The latter species has incomplete translamella, which in the former species is absent, and differs from it also by the length:width ratio of the notogaster and pteromorph (Table 3).

The tritonymph of L. solhoyorum differs from that of L. rugosus in few morphological characters (Table 4). The former species has higher number of longer setae on the gastronotum than the latter species both in the larva (lp, h₁, h₂, and lm, respectively) and nymphs (p₁, h-series, and lp, h₁, h₂, respectively), and differs also from it by the shape of setae in and h₃ in the larva. Moreover, the shape of leg setae and solenidia of the adult and tritonymph of L. rugosus (Figs. 20, 21) is similar as in L. solhoyorum presented above, but the ontogeny of setae differs in these species. In L. rugosus, seta l" is more often added on femora I and II than in L. solhoyorum, l" can appear on tibia II in the deutonymph or tritonymph (versus in tritonymph in L. solhoyorum), and l' appears in the deutonymph (versus in the tritonymph in adult of L. solhoyorum). The shape of body, palp and leg setae, solenidia and famulus ε of tritonymph of L. rugosus (Figs. 21, 22) is similar as in the tritonymph of L. solhoyorum (Figs. 14–17).