The morphological ontogeny of Cosmochthonius oralensissp. nov. from West Kazakhstan is described and illustrated. The adult of this species has thin cerotegument and microfoveae on the pygidium, as has C. minifoveolatusGil et al., 1991, but the latter species is smaller than C. oralensis and its basal cilia on erected setae of f-series are distinctly longer than on setae of e-series; in C. oralensis these cilia are of similar length. The juveniles of both species are similar to adults, except for smaller body size and more delicate cuticle of juveniles. These species also differ from each other by the number of cilia on erected setae, both in the juveniles and adults. The morphology of C. oralensis is compared with congeners.
Cosmochthonius Berlese, 1910 comprises medium sized mites (250–360 µm) as adults. These mites are elongated, with many heavily barbed or bushy setae on the main body and legs. Cosmochthonius belongs to the lower Oribatida and has four plates on the notogaster (Weigmann 2006), which are connected with thin cuticle, making the body elastic while squeezing through soil pores. This genus has four pairs of long, strong, barbed and erected setae, which are inserted on transverse intercalar sclerites on the notogaster (Grandjean 1931). After erection, these setae enlarge the body size of mites, protecting them to a certain degree against small predators. Most species of Cosmochthonius are covered with a thick layer of cerotegument (Gordeeva 1980; Ayyildiz & Luxton 1990; Gil et al. 1991; Penttinen & Gordeeva 2010), which probably limits intensive water evaporation from the body, but there are also species with thin cerotegument, like Cosmochthonius oralensis sp. nov. from West Kazakhstan studied herein. This species has irregular microfoveae on the pygidium, which are rare in Cosmochthonius. Pygidial microfoveae also occur on C. minifoveolatus Gil et al., 1991, but this species is smaller than C. oralensis and has basal cilia on erected setae of f-series distinctly longer than on setae of e-series; in C. oralensis, these cilia are of similar length. In most species of Cosmochthonius, the pygidium is reticulate or with foveae. The Cosmochthonius species also differ from one another by the number of cilia on erected setae. The juveniles of Cosmochthonius are similar to adults, except for smaller body size and more delicate cuticle of juveniles (Seniczak & Seniczak 2010; Seniczak et al. 2011). Cosmochthonius comprises 32 species and two subspecies (Subías 2019).
In the catalogue of juvenile oribatid mites, Norton and Ermilov (2014) listed four species of Cosmochthonius with full ontogeny, which constitute 12% of all species of this genus. These species are: C. foliatus Subías, 1982, C. ponticus Gordeeva, 1980, C. reticulatus Grandjean, 1947 and C. ugamaensis Gordeeva, 1980. A nymph of C. lanatus (Michael 1885) is also known.
The aim of this paper is to describe and illustrate the morphological ontogeny C. oralensis sp. nov. and compare the morphology of this species with congeners.
Material, methods and terminology
The juveniles and adults of C. oralensis sp. nov. used in this study were collected on 21 November 2018 by S. Kaczmarek from the litter of Scots pine (Pinus sylvestris L.), about 50–60 years old, which was planted in lines 30–50 m wide, in a steppe of West Kazakhstan (Uralsk surroundings, 51.2753°N, 52.1322°E, 40 m a. s. l.). Illustrations were prepared from individuals mounted temporarily on slides in lactic acid, using the open-mount technique (Grandjean 1949). We measured total length (from tip of rostrum to posterior edge of notogaster) and width (widest part of notogaster) of mites, and length of setae and some parts of the body of mites in µm. The illustrations of instars of C. oralensis are limited to the body regions of mites that show substantial differences between instars, including the dorsal and lateral aspects and some leg segments of the larva, tritonymph and adult, ventral regions of all instars, and chelicera and palp of the adult. We also investigated leg setae and solenidia, chelicera and palp of C. foliatus, which were omitted by Seniczak et al. (2011). The latter species originated from cypress litter in Santa Susana (Costa Brava, North-East Spain, 41.3726°N, 2.4324°E, 4 m a. s. l.). In the text and figures, we used the following abbreviations: rostral (ro), lamellar (le), interlamellar (in) and exobothridial (exs, exi) setae, bothridium (bo), bothridial seta (bs), notogastral or gastronotal setae (c-, d-, e-, f-, h-, p-series), notogastral or gastronotal plates (Na, Nm1, Nm2, Py), genital (G) aggenital (Ag), adanal (Ad) and anal (An) plates, cupules (ia, im, ip, ih, ips, iad), epimeral setae (1a–c, 2a, 2b, 3a–c, 4a–d), adanal and anal setae (ad-, an-series), subcapitular setae (a, m1, m2, h), cheliceral setae (cha, chb), palp setae (sup, inf, l, d, cm, acm, lt, vt, ul, su) and solenidion ω, leg solenidia (φ, ω), famulus (ε) and setae (bv, ev, d, l, ft, tc, it, p, u, a, s, pv, pl, v). Terminology used follows that of Grandjean (1931, 1947, 1949, 1953) and Norton and Behan-Pelletier (2009). The species nomenclature follows Subías (2004, 2019).
For scanning electron microscopy (SEM), the mites were air-dried and coated with Au/Pd in a Polaron SC502, sputter coater and placed on Al-stubs with double-sticky carbontape. Observations and micrographs were made with a ZEISS Supra 55VP scanning electron microscope.
Adults of medium size (287–323), yellowish-brown, with characters of Cosmochthonius. Pygidium with thin cerotegument and microfoveae of irregular size. Setae of c-series longer than those of d-series. Seta c1 longer than d1, erected setae of e- and f-series with 18–20 pairs and 16–18 pairs of cilia, respectively, setae and basal cilia of both series of similar length. Legs II–IV tridactylous.
Juveniles uncoloured, cuticle more delicate than in adult. Setae of c- and d-series as in adult, erected setae (e- and f-series) with 11–15 pairs, and 9–12 pairs of cilia in larva, and 15–18 and 11–14 pairs in tritonymph, respectively. In larva, basal cilia on erected setae of similar length, in tritonymph, basal cilia on setae of f-series slightly longer than on setae of e-series.
Morphology of adult
Measurements. Body length and width of holotype (305, 155, respectively), length and width (and range) of other females—306.9 (287–323, n= 17), 156.8 (142–172), respectively.
Prodorsum. Rostrum rounded and wide in dorsal and ventral aspects (Figs. 1b, 2), rostral fenestration comprises rounded alveoli in anterior 1–3 rows and elongated alveoli in posterior row (Figs. 1a, 1b). Rostral setae bushy or barbed (Figs. 1b, 2, 3a, 4a–c, 5b, 5c). Five pairs of setae present, including two pairs of exobothridial setae (exs, exi, Figs. 1b, 3a); all bushy, except for barbed exi. Seta ro slightly longer than le, both curved inwards, seta in curved anterior. Mutual distance between insertions of setae ro slightly longer than between setae le and in. Bothridium rounded, protruding above surface, bothridial seta long, with barbed apical half (Figs. 1b, 3a, 4a–c, 5c). Prodorsum yellowish-brown, covered with thin granular cerotegument, some parts with thicker cerotegument (Fig. 6d).
Notogaster. Elongated, egg-shaped, with 16 pairs of setae and three transverse scissures, dividing notogaster into four plates (Figs. 1b, 3a, 4), Py longest, Nm2 shortest. Plate Na with four pairs of setae, c1–c3 in anterior row and cp in posterior row; all of medium size (Table 1) and pinnate; cp longest, c2 shortest. Plate Nm1 with two pairs of setae (d1, d2), shorter than c-series and with shorter barbs. Transverse intercalar sclerites present between plates Nm1 and Nm2, and Nm2 and Py, each with two pairs of long, hypertrophied and erected setae (e- and f-series, respectively). Setae of e- and f-series with 18–20 and 16–18 pairs of cilia, respectively, all pinnate, basal cilia of each series of similar length. When not erected, all erectile setae protrude behind anterior part of pygidium. Pygidium with six pairs of bushy setae (h-, p-series) and irregular microfoveae (Figs. 1c, 4d, 5a). Lyrifissures ia and im posterolateral to setae c3 and cp, respectively, lyrifissure ip posterior to seta p3, and lyrifissure iad lateral to anterior part of adanal plate (Figs. 2, 3a). Other lyrifissures not observed. Notogaster yellowish-brown, covered with thin granular cerotegument. Lateral sides of hysterosoma with denser microfoveae than on pygidium, also observed as small net (Figs. 3b, 5a, 6a, 6b).
Gnathosoma. Subcapitular seta h longer (23) than m1, m2 and a (11), all barbed (Fig. 2). Chelicera (length 47–49, width 21) with two setae of similar length (13), cha setiform, chb with comb-form distal part (Fig. 3c). Palp (length 60–62) with smooth setae (Fig. 3d), except for barbed sup, palpal eupathidium acm separated from solenidion ω, eupathidia ul1 and ul2 setiform and relative long, su shorter and barbed. Formula of palp setae (trochanter to tarsus + solenidion ω): 0-2-1-3-9(1).
Ventral and lateral aspects. All epimeral setae barbed (Fig. 2), formula of epimeral setae 3-2-3-4. Ten pairs of genital setae present of different lengths. Based on appearance of setae in ontogeny, g1, g3, g5 and g7 longer than other setae (Figs. 2, 7a). Elongated aggenital plate lateral to genital plate, but aggenital seta absent. Anadal and anal plates with four pairs of setae each, all barbed, but setae of ad-series longer than of an-series; setae of ad-series of similar length, but an1 longer than an2–4. Anal plate with short longitudinal lines. Ventral and lateral parts of hysterosoma yellowish-brown and covered with thin granular cerotegument.
Legs. Most leg setae barbed, but dorsal and lateral setae of femora, genua and tibiae with longer barbs than other setae (Fig. 8). Solenidion φ on tibia I long, on large apophysis, directed anterior and pliable, solenidion ω on tarsi I and II shorter and curved anterior, other leg solenidia short; famulus ε on tarsus I relatively long. Solenidion σ on all genua absent, but seta d present on all femora, genua and tibiae. Formula of leg setae and solenidia: I—1-5-5-5(1)-20(1); II—1-6-5-5(1)-17(1); III—2-3-4-4(1)-15; IV—2-3-4-4(1)-13. Leg I heterobidactylous, legs II–IV heterotridactylous.
Description of juvenile stages
Larva oval, unpigmented, usually distended in lactic acid. Prodorsum relatively long (Table 1), subtriangular, with rounded, wide rostrum, and with small, fenestrate areas (Fig. 9). Prodorsal setae ro, le, in and exs with long basal barbs, curved, uniramous, cilia on setae single, except for bifurcate basal cilia of setae le and exs; seta exi distinctly shorter and barbed. Bothridium rounded, bothridial seta long, with narrow, and barbed apical half.
Gastronotum of larva with 14 pairs of setae (Figs. 9, 10a, 11a), including inguinal h4 positioned anterior to paraproctal valves (segment PS). Pygidial plate weakly developed, with three pairs of barbed setae of h-series, h3 shorter than h1 and h2. Seta h1 pinate (with about 7 cilia), other setae of hseries barbed. Gastronotum with three transverse scissures, which divide it into four plates. Plate Na with four pairs of setae; c1–c3 in anterior row, cp in posterior row; all long and barbed, c1 and c2 reaching anterior board of plate Nm1, cp hardly reaching anterior board of plate Nm2. Plate Nm1 with two pairs of setae (d1, d2), shorter than of c-series and barbed, not reaching anterior intercalary sclerites. Setae of e- and of f-series hypertrophied, erectile, pinnate, inserted on intercalary sclerites, located between plates Nm1 and Nm2, and Nm2 and pygidium (Py), respectively. Setae of e- and fseries with 13–15 and 9–12 pairs of cilia, respectively, basal cilia of each series of similar length. Paraproctal valves with four pairs of barbed setae, slightly shorter than h4. Cupule ia posterior to seta c3, cupule im posteroventral to seta cp, cupule ip anterior to seta h3, cupule ih lateral to seta p4 (Figs. 10a, 11a). Ventral parts of gastronotum weakly striated. Leg setae of larva barbed (Fig. 12). Solenidion φ on tibia I long, solenidion ω on tarsi I and II of medium size, other leg solenidia short, famulus ε on tarsus I relatively long.
Nymphs more slender than larva, most prodorsal setae bushy, except for barbed exi. Bothridium relatively smaller than in larva, but bothridial seta as in larva. Gastronotum of protonymph with 16 pairs of setae due to lost inguinal seta h4 and p4, and transfer of three pairs of p-series setae from paraproctal valves to gastronotum (Fig. 10b), retained in deutonymph and tritonymph (Figs. 13a, 13b), all of medium size (Table 1), curved and barbed; in protonymph and deutonymph, p1 and p2 longer than p3, in tritonymph all setae of similar length. In all nymphs, three transverse scissures present, which divide gastronotum in four parts. Number and distribution of setae on plates Na, Nm1 and Nm2 as in larva, but pygidium with six pairs of setae (h- and p-series); all of medium size and barbed (Table 1). Setae of c-series longer than of d-series, and barbed, erectile setae of e- and f-series pinnate. In tritonymph, setae of e- and f-series with 15–18 and 11–14 pairs of cilia, respectively, basal cilia on setae of f-series slightly longer than on setae of e-series (Figs. 11b, 14). Protonymph with one pair of medium sized genital setae, and two pairs of similar setae added in deutonymph, and four pairs in tritonymph (one pair medium sized and three pairs of short setae, Figs. 13a, 13b), all barbed. In deutonymph four pairs of adanal setae present on segment AD, which remain in tritonymph. Paraproctal valves of protonymph (segment AD), deutonymph and tritonymph (segment AN) with four pairs of setae; anal barbed and shorter than adanal setae. Aggenital plate and setae absent. Anogenital region of nymphs with gentle striae. Dorsal and lateral setae on femora and genua I and II with longer barbs than in larva (Fig. 15), but shape of leg solenidia as in adult.
Summary of ontogenetic transformations
The number of prodorsal setae is constant during the ontogeny of C. oralensis (5 pairs, including bothridial setae), and the shape of these setae remains similar, but the number of gastronotal setae increases from 14 pairs in the larva to 16 pairs in the nymphs and adult (inguinal h4 and p4 lost, p1–p3 present). All instars have three transverse scissures on the dorsal part of hysterosoma, and hypertrophied, erectile and pinnate setae of e- and f-series, which are inserted on transverse intercalary sclerites. Aggenital setae are absent. The formula gastronotal setae is 14-16-16-16-16, whereas the formulae of epimeral, genital, and segments PS–AN are as in C. ponticus (Seniczak & Seniczak 2010). The ontogeny of leg setae is given in Table 2.
Distribution, ecology and biology
Cosmochthonius oralensis was found in a dry Scots pine litter in a steppe of West Kazakhstan. In this sample, the density of this species was 46 individuals per 500 cm3, and the juveniles constituted 67% of the total population. The stage structure of C. oralensis was the following: one larva, two protonymphs, 16 deutonymphs, 10 tritonymphs and 17 adults. No gravid female was observed in a sample population.
Type material deposition
Holotype female and three paratypes (females) are deposited in the University Museum of Bergen, University of Bergen, Bergen, Norway.
The species name follows the Kazakhstanis name Oral (Uralsk), in which surroundings this species was found.
Measurements of some morphological characters of juvenile stages of Cosmochthonius oralensis (mean measurements of 1–10 individuals per instar in µm); Nd—not developed.
Ontogeny of leg setae (Roman letters) and solenidia (Greek letters) in Cosmochthonius oralensis.
Comparison of morphology of Cosmochthonius oralensis with congeners and remarks
Among Cosmochthonius species, the largest is C. foveolatus Beck, 1962, and smallest is C. maroccanus Gil et al., 1992, and the body length of most species overlaps (Table 3). In C. asiaticus Gordeeva, 1980 and C. desaussurei Mahunka, 1982, the pygidium has no distinct pattern, in C. minifoveolatus Gil et al., 1991, and C. oralensis sp. nov. it has microfoveae, whereas in other species the pygidium is either foveolate or reticulate. Cosmochthonius species also differ one from another by the number and shape of cilia on erected setae, shape of setae of c-and d-series, and number of genital setae and claws on legs II–IV (Table 3). From this comparison it is evident that C. oralensis is similar to C. minifoveolatus, but the latter species is smaller than C. oralensis and its basal cilia on setae of f-series are distinctly longer than those of e-series, whereas in C. oralensis these cilia are of similar length.
Selected morphological characters of adults of Cosmochthonius species.
Seniczak et al. (2011) compared the juveniles of C. foliatus, C. reticulatus, C. ponticus and C. ugamaensis, and it is possible to find some differences between these species and C. oralensis. In the larva of C. oralensis, the number of pairs of cilia on erected setae of e- and f-series is similar to that of C. foliatus, whereas C. reticulatus has fewer cilia and C. ponticus and C. ugamaensis have more cilia than C. oralensis. In C. oralensis, the basal cilia on setae f1 and e1 are of similar length, as in C. foliatus, whereas in C. reticulatus, C. ponticus and C. ugamaensis the basal cilia on seta e1 are longer than on seta f1. In C. oralensis, seta h1 is pinnate, as in C. foliatus, C. reticulatus and C. ugamaensis, whereas in C. ponticus has this seta is bushy. In C. oralensis, the number of cilia on seta h1 is similar to that of C. foliatus and C. ugamaensis, whereas C. reticulatus has fewer cilia and C. ugamaensis has more cilia than C. oralensis. Cosmochthonius oralensis also differs from other species by the shape of setae of d- and h-series and p1.
In the nymphs of C. oralensis, the number of pairs of cilia on erected setae of e- and f-series is similar to that of C. ugamaensis, whereas C. foliatus and C. ugamaensis have more cilia, and C. ponticus has fewer cilia than C. oralensis. In C. oralensis, the basal cilia on setae of e- and f-series are of similar length, as in C. foliatus, whereas in other species the basal cilia on seta e1 are longer than on seta f1. From these comparisons it is evident that the juveniles of C. oralensis differ from other species mainly by the number and shape of cilia on erected setae. In the nymphs, the shape of setae of d- and h-series and p1 is also important.
The chelicerae of C. oralensis and C. foliatus are typical of Cosmochthonius, by having two setae of different shape, cha setiform and chb with comb-form distal part (Grandjean 1947; Beck 1962; Lee 1982). In both species, seta cha is smooth, but in C. foliatus the combs of seta chb are slightly longer (Fig. 7c) than in C. oralensis (Fig. 3c). In C. australicus Womersley, 1945, seta cha (Lee 1982) is smooth as in C. oralensis and C. foliatus, whereas in C. reticulatus and C. domesticus Grandjean, 1947 [= C. lanatus (Michael 1885)], C. foveolatus Beck, 1962 and C. nayoroensis Fujikawa, 1980 this seta is barbed. Grandjean (1947) used the shape of chelicera to separate C. reticulatus from C. domesticus.
The number and location of palp setae of C. oralensis are similar as in C. foliatus, but the shape of some setae differs, especially sup. In the former species, this seta is barbed (Fig. 3d), whereas in the later species it has rare and long cilia (Fig. 7d). In both species, two long setae are observed on the palpal tarsus, probably cm and acm, as in C. foveolatus (see Beck 1962) and C. australicus (see Lee 1982), but the former author noted 10 palpal setae, whereas the latter author illustrated nine setae, as in C. oralensis and C. foliatus. However, it is difficult to discuss the differences in the number and shape of palp setae because the notation of these setae by Beck (1962) and Lee (1982) differs from that of C. oralensis and C. foliatus.
The ontogeny of leg setae and solenidia of C. oralensis is similar to that of C. foliatus. In both species, most leg setae are added in the protonymph and deutonymph, and solenidion σ is absent from genua I–III. The distribution of leg setae and solenidia in the adult of C. foliatus (Fig. 16) is similar to that of C. oralensis (Fig. 8), but the shape of some setae differs. In C. foliatus, the dorsal and lateral setae on femora and genua I–IV are bushy or have longer barbs than in C. oralensis, and a thick layer of cerotegument is present between some setae, which is absent in C. oralensis. In the tritonymph of C. foliatus (Fig. 17), the dorsal and lateral setae on femora and genua I–IV are slightly shorter than in the adult, and a thick layer of cerotegument is absent. In the adults of most other species of Cosmochthonius, only the number of leg claws is known, whereas the formulae of setae and solenidia is known in C. nayoroensis, C. taurus and C. zanini (Fujikawa 1980; Niemi et al. 2002; Penttinen & Gordeeva 2003), and formulae of legs I–III in C. austalicus (Lee 1982). In all species, the number of leg setae is similar to that of C. oralensis and C. foliatus, except for tarsus IV (two latter species has one seta less than other species), and tarsus I of C. nayoroensis (it has one seta less than C. oralensis and C. foliatus). All these data indicate that hat the shape of chelicera, palp and leg setae of Cosmochthonius can be diagnostic and needs more investigation.
Kaczmarek S. would like to thank Prof. Dr. B. Alzhanova and Prof. Dr. T.T.E. Darbaieva (Department of Biology and Ecology, M. Utemisov West Kazakhstan State University) for assistance in arranging his stay in the Department of Biology and Ecology and sampling. We thank two anonymous reviewers for helpful suggestions that improved the scientific value of this paper. This study was done under the program of the Polish Minister of Science and Higher Education "Regional Initiative of Excellence" in 2019–2022 (Grant No. 008/RID/2018/19).