Oribatula pannonica Willmann, 1949

Seniczak, Stanisław, Ivan, Otilia & Seniczak, Anna, 2024, Morphological ontogeny of Oribatula pannonica (Acari, Oribatida, Oribatulidae), and comments on some species of Oribatula Berlese, Zootaxa 5485 (1), pp. 106-129 : 107-114

Oribatula pannonica Willmann, 1949

( Figs 1–14 )

Diagnosis. Adult of medium size (length 385–482), with characters of Oribatula given by Seniczak et al. (2023). Translamella absent, bothridial seta fusiform. Notogaster with anterior shoulder and 13 pairs of setae (p 3 absent), most of medium size and smooth. Notogastral porose areas (4 pairs) small, oval, Aa slightly larger than other porose areas.

Most prodorsal setae of juveniles of medium size, bothridial seta clavate. Larva with 11 pairs of gastronotal setae, including h 2, most of medium size and barbed, nymphs with 14 pairs (p 3 absent), most short and smooth. In larva basal excentrosclerites present at nine pairs of gastronotal setae (c 1, c 2, d -, l -series, h 1), and in nymphs at 12 pairs (c 1, c 2, d -, l -, h -series, p 1).

Morphology of adult. Morphology of adults ( Figs 1–5 , 6a, 6b , 7 ) similar to that described by Willmann (1949) but see Remarks. Mean length (and range) of females 449.5±15.9 (422–482, n= 144) and males 414.6±11.9 (385– 440, n= 66), mean width (and range) of females 263.8±14.3 (235–301) and males 238.2±7.1 (223–253). Prodorsal setae ro, le, in and bs long, ex of medium size ( Table 1 ), all finely barbed ( Figs 1 , 3a , 4 , 5a, 5b ). Cerotegument microporose, thin, many pits and granular cerotegument present between lamella and basal parts of legs ( Figs 3a , 4a, 4b, 4d , 5a, 5b ). Notogastral setae (13 pairs, including c 1 and c 2, p 3 absent) of medium size ( Table 1 ) and smooth, porose areas (4 pairs) small, oval, Aa slightly larger than other porose areas, opisthonotal gla opening located anterolateral to seta lp ( Figs 1a , 3a , 4 , 5 ). Lyrifissure ia posterolateral to seta c 2, im anterior to seta lp, ip between setae p 1 and p 2, ips and ih anterior to seta p 2 ( Figs 1a , 3a ). Subcapitular setae h, m and a short and finely barbed ( Figs 2 , 4c , 6a ). Chelicera chelate-dentate, with short, finely barbed setae, cha slightly longer than chb ( Fig. 3b ), palp relatively short, most setae of medium size and finely barbed ( Fig. 3c ), formula of palp setae (trochanter to tarsus + solenidion ω): 0-2-1-3-9(1). Epimeral, genital, aggenital, anal, and adanal setae short and smooth ( Figs 2 , 4b, 4c , 6b ), adanal lyrifissure iad anterior to anal plate. All femora flattened, with ventral carina, most leg setae with short barbs ( Figs 4 , 6a , 7 ). Formulae of leg setae (and solenidia), trochanter to tarsus: I—1-5-(3+1)-(4+2)-(20+2); II—1- 5-(2+1)-(4+1)-(15+2); III—2-3-(1+1)-(3+1)-15; IV—1-2-2-(3+1)-12. Leg tarsi heterotridactylous.

Remarks. The mean body size of adults investigated here is slightly larger of that described by Willmann (1949: length 400, width 240), Bulanova-Zachvatkina (1975: length 400) and Weigmann (2006: length 350–470); a sex ratio was not investigated in these papers. The body shape and distribution of prodorsal and notogastral setae are similar as in these papers. The anterior part of notogaster of the adult drawn by Willmann (1949) is wider than in our individuals, which might be a result of the preparation technique.

Description of juvenile stages. Larva oval in dorsal and ventral aspect ( Figs 8a , 9a ) and unpigmented. Prodorsum subtriangular, most prodorsal setae of medium size except for long ro ( Table 1 ), and short ex, all finely barbed. Mutual distance between setal pair le slightly longer than the distance between setal pair ro, and mutual distance between setal pair in over three times longer than that of setal pair ro, seta le inserted slightly closer to seta in than to seta ro ( Figs 8 , 10a ). Bothridium rounded, bothridial seta of medium size and clavate, with thick, barbed head. Prodorsal shield well-developed.

Gastronotum of larva weakly developed with 11 pairs of setae, including h 2 located laterally to medial part of anal valves, all of medium size ( Table 1 ) and finely barbed ( Figs 8 , 9a , 10a ). Setae c 1, c 2, d -, l -series, and h 1 with basal excentrosclerites, c 3, h 2 without excentrosclerites, most excentrosclerites small except for larger excentrosclerite at seta c 2. Cupule ia posterior to seta c 3, cupule im posterior to seta lm, cupule ip between setae h 1 and h 2, cupule ih lateral to anterior part of anal valves, opisthonotal gland opening gla anteroventral to seta lp ( Figs 8a , 9a , 10a ). Paraproctal valves (segment PS) with two pairs of short and smooth setae. Most leg setae of medium size and finely barbed ( Fig. 11 ).

Prodorsum and prodorsal setae of protonymph as in larva, but head of bothridial seta slimmer than in larva. Gastronotum of protonymph with 14 pairs of setae because of the addition of seta h 3 and two pairs of larval paraproctal setae remain as p -series setae (p 1 and p 2), also present in deutonymph and tritonymph ( Figs 9b , 10b , 12 ), most short and smooth except for finely barbed c 3. In protonymph, one pair of genital setae appearing, and one pair added each in deutonymph and tritonymph, all short and smooth. In deutonymph, one pair of aggenital setae and three pairs of adanal setae appearing and present in tritonymph, all short and smooth ( Figs 10b , 12 ). Most gastronotal setae of tritonymph short and smooth, except for finely barbed c 3 ( Figs 12b , 13 ). Basal excentrosclerites at setae c 1, c 2, d -, l -, h -series and p 1, other setae (c 3, p 2) without excentrosclerites, most excentrosclerites small except for larger excentrosclerite at seta c 2. Paraproctal valves of protonymph and deutonymph glabrous, those of tritonymph with two pairs of short and smooth setae. In tritonymph cupules ia and im located as in larva, cupule ip between setae h 2 and p 1, cupule iad lateral to anterior part of paraproctal valves, cupule ips and ih pushed lateral to cupule iad ( Figs 10b , 12b , 13 ). Gland opening gla located laterally to seta lp. Most leg setae of medium size and finely barbed ( Figs 6c, 6d , 14 ). Seta v’ on genu I present, but on genu II absent.

Summary of ontogenetic transformations. In all juveniles of O. pannonica the prodorsal seta ro is longest, and seta ex is shortest, whereas in the adult most setae are long, except for medium-sized ex. In all instars, the bothridium is rounded, but in the juveniles the bothridial seta is clavate and in the adult it is fusiform. The larva has 11 pairs of gastronotal setae, including h 2, the nymphs have 14 pairs (h 3 is added in protonymph, two pairs of larval paraproctal setae remain as p 1 and p 2), while the notogaster of adult loses seta c 3, and 13 pairs of setae remain. The formula of gastronotal setae in O. pannonica is 11-14-14-14-13 (larva to adult), and those of epimeral setae are: 3-1- 2 (larva), 3-1-3-1 (protonymph), 3-1-3-2 (deutonymph) and 3-1-3-3 (tritonymph and adult). The formula of genital setae is 1-2-3-4 (protonymph to adult), that of aggenital setae is 1-1-1 (deutonymph to adult), and the formula of segments PS–AN is 22222-0333-022. Ontogeny of leg setae and solenidia is similar as in O. heterochaeta ( Seniczak et al. 2023) , except for seta v’ on genu I, which is added in O. pannonica in the tritonymph, and in O. heterochaeta in the adult.

Distribution, ecology and biology. Oribatula pannonica has a Palaearctic distribution ( Subías 2004, 2024).This species was recorded from Central and Eastern Europe, i.e. from Austria ( Krisper et al. 2017), Czech Republic ( Miko 2016), Poland ( Niedbała & Olszanowski 2008), Hungary ( Mahunka & Mahunka-Papp 2004), Slovenia, Croatia, Bosnia and Herzegovina, Montenegro ( Tarman 1983), Romania ( Vasiliu et al. 1993), and Caucasus ( Shtanchaeva & Subías 2010). In was also found in Central Asia ( Karppinen et al. 1986) and Mongolia ( Bayartogtokh 2010).

In Romania, this species was recorded in forests ( Ivan & Vasiliu 2000), in meso-xerophilous meadows ( Ivan 2007), saxicolous habitats ( Ivan & Călugăr 2004) and cultivated soils ( Ivan & Călugăr 2013). However, it was most frequent and abundant in some meadows and cultivated soils, both with annual and perrennial crops, indicating its preference to agricultural habitats. Weigmann (2006) noted the preference of O. pannonica to dry soils and mosses on stones, and its tolerance to soil salinity. This species was less abundant in grazed meadows than in those used as hayfields ( Ivan 2007). It was abundant in meadows in the dammed area but was absent from soil of flooded meadows ( Ivan 2009) and was neither abundant nor frequent in forest soils (Ivan 2013). In Mongolia O. pannonica was found in the litter of birch forests and the soil of mountain and plain steppes ( Bayartogtokh 2010). The data collectively indicate a large ecological plasticity in this species.

In this study, O. pannonica was the most abundant in perennial crop in BuhăieŞti, and the least abundant in perennial crop in StănileŞti ( Table 2 ), while being relatively abundant in the urban garden in IaŞi, mesophilous meadow in StănileŞti, hayfield in TomeŞti and forest nursery in Guranda. Furthermore, females in the meadow in TomeŞti and StănileŞti were significantly wider than those in the urban garden in IaŞi, which might have been caused by the larger number of eggs carried by females in TomeŞti and StănileŞti ( Table 3 ). Females from the meadow in TomeŞti and StănileŞti, lucerne in BuhăieŞti, and forest nursery in Guranda were significantly longer than males from these habitats, whereas the other measurements of adults given in Table 3 were statistically insignificant.

The juveniles of O. pannonica were the most abundant in the urban garden in IaŞi, constituting 34% of species population with the stage structure as follows: 5 larvae, 6 protonymphs, 3 deutonymphs, 6 tritonymphs and 38 adults. Out of the 210 adults investigated, the sex ratio (females to males) was 1:0.46 ( Table 2 ). Most females (66%) were gravid carrying 1–9 large eggs (usually 2– 4 eggs), each 160 × 87, constituting 36% of body length of females .

Figures

FIGURE 1. Oribatula pannonica, female. (a) Dorsal aspect, legs partially drawn, scale bar 50 μm; (b) shape of seta le (enlarged).

FIGURE 2. Oribatula pannonica, female, ventral aspect, legs partially drawn, scale bar 50 μm.

FIGURE 3. Oribatula pannonica, female. (a) Lateral aspect, legs partially drawn, scale bar 50 μm; mouthparts, right side, scale bars 20 μm; (b) chelicera (Trägårdh organ indicated in a transparent area), (c) palp.

FIGURE 4. Oribatula pannonica, adult, SEM micrographs. (a) Dorsal view; (b) lateral view; (c) ventral view; (d) anterior and medial part of body, dorsal view.

FIGURE 5. Oribatula pannonica, adult, SEM micrographs. Lateral view, (a), (b) bothridial seta; (c), (d) gla opening.

FIGURE 6. Oribatula pannonica, SEM micrographs. Adult, (a) subcapitulum, ventral view; (b) genital plates, lateral view; tritonymph, ventral view, (c) leg I and II; (d) leg III and IV.

FIGURE 7. Oribatula pannonica, leg segments of adult (part of femur to tarsus), right side, antiaxial aspect, scale bar 20 μm. (a) Leg I, tarsus (pl’ not illustrated); (b) leg II; (c) leg III; (d) leg IV.

FIGURE 8. Oribatula pannonica, larva. (a) Dorsal aspect, legs I and II partially drawn, scale bar 20 μm; (b) shape of seta dp (enlarged).

FIGURE 9. Oribatula pannonica, ventral part of hysterosoma, legs III and IV partially drawn, scale bar 20 μm. (a) Larva, (b) protonymph.

FIGURE 10. Oribatula pannonica, lateral aspect, legs partially drawn, scale bars 20 μm. (a) Larva, (b) tritonymph.

FIGURE 11. Oribatula pannonica, leg segments of larva (part of femur to tarsus), right side, antiaxial aspect, scale bar 10 μm. (a) Leg I, tarsus (pl’ not illustrated); (b) leg II; (c) leg III.

FIGURE 12. Oribatula pannonica, ventral part of hysterosoma, legs IV partially drawn, scale bar 50 μm. (a) Deutonymph, (b) tritonymph.

FIGURE 13. Oribatula pannonica, tritonymph. (a) Dorsal aspect, legs partially drawn, scale bar 50 μm; (b) shape of seta c3 (enlarged).

FIGURE 14. Oribatula pannonica, leg segments of tritonymph (part of femur to tarsus), right side, antiaxial aspect, scale bar 20 μm. (a) Leg I, tarsus (pl’ not illustrated); (b) leg II; (c) leg III; (d) leg IV.

Tables

TABLE 1. Measurements of some morphological characters of instars of Oribatula pannonica (mean measurements of 3–10 specimens in μm); nd—not developed.

Morphological characters		Larva	Protonymph	Deutonymph	Tritonymph	Adult
Body length		198	264	310	416	430
Body width		99	135	132	182	248
Length of prodorsum		69	69	105	115	125
Length of:	seta ro	22	24	32	43	58
	seta le	12	15	23	27	68
	seta in	15	17	26	35	61
	seta bs	27	30	35	38	49
	seta c 1	12	11	12	10	32
	seta c 2	9	9	9	8	23
	seta c 3	12	12	13	12	lost
	seta da	11	9	8	10	29
	seta dp	10	10	9	11	33
	seta la	10	9	8	10	28
	seta lp	11	10	9	11	37
	seta h 1	15	11	11	10	33
	seta h 2	10	10	10	10	29
	seta h 3	nd	8	10	10	33
	seta p 1	nd	10	11	10	24
	seta p 2	nd	9	9	9	26
genital opening		nd	26	44	58	52
anal opening		31	47	71	97	74