The morphological ontogeny of Proteremaeus oralensissp. nov. from the elderberry litter (Sambucus nigra L.) from Kazakhstan is described and illustrated. The adult of this species is the most similar to that of P. macleani Behan-Pelletier, 1982, but differs from it mainly in the shape of lamellar complex, posterior notogastral tip, distribution of genital setae, and some leg characters. The juveniles of P. oralensis are oval, light-brown, with short prodorsal and gastronotal setae and clavate bothridial seta. The nymphs are quadrideficient and eupheredermous, i.e. they lack setae of d-series and carry the exuvial scalps of previous instars on the gastronotum. In the nymphs, setae p1 and h1 are inserted close to each other, and seta h2 is placed approximately at similar distances from seta p1 and p2.
Introduction
While working on the oribatid mites from elderberry litter (Sambucus nigra L.) from Kazakhstan, we found a new species from Proteremaeus Piffl, 1965 (Eremaeidae), which was rather abundant and included all developmental instars. This species was the only member of Eremaeidae, so the juveniles and adults undoubtedly belong to it.
Proteremaeus, with the type species P. jonasi Piffl, 1965 comprises nine nominative species that occupy a Paleartic region (Subías 2004, updated 2020). Diagnosis of the adult of this genus gave Behan-Pelletier and Rjabinin (1991), with the main morphological characters: lamellar seta at tip of lamellar costula, interlamellar seta lateral of lamellar costula and anterior of bothridium; notogaster with 10 or 11 pairs of setae, each with porose ring; discidium present, two pairs of anal and three pairs of adanal setae, ventral plate heavily sclerotized posteriorly, femora with unequal paraxial and antiaxial carinae.
The juvenile stages of Proteremaeus are insufficiently known. Based on the catalogue of oribatid juveniles by Norton and Ermilov (2014), the full morphological ontogeny of P. punctulatus Bayartogtokh, 2000 has been described, which constitutes 11% of all species of this genus.
The aim of this paper is to describe and illustrate the morphological ontogeny of P. oralensis sp. nov., and compare the morphology of this species with congeners.
Material and methods
The juveniles and adults of P. oralensis for this study were collected on 11 July 2019 by Kaczmarek S. from moist litter under elderberry (Sambucus nigra L.) growing dense on a slope (150–200 m2) in a meadow plain, about 10 m from Derkul river, one km east from Dachi-Novostroyka village (51°16′49″N, 51°17′70″E, 52 m a. s. l., West Kazakhstan). In this habitat, we investigated the density and stage structure of mites, and based on 30 randomly selected specimens, the sex ratio, number of gravid females and carried eggs, and length and width of the body. We measured total body length (from tip of rostrum to posterior edge of notogaster) in lateral aspect and body width (widest part of notogaster) in dorsal aspect, and size of anal and genital openings and setae perpendicularly to their length in µm.
The illustrations of instars are limited to the body regions of mites that show substantial differences between instars, including the dorsal and lateral aspect and some leg segments of the larva, tritonymph and adult, and ventral regions of all instars. Palp and chelicera of the adult are also illustrated. Illustrations were prepared from individuals mounted temporarily in lactic acid. In the text and figures we used the following abbreviations: rostral (ro), lamellar (le), interlamellar (in) and exobothridial (ex) setae, lamellar costula (Cos), bothridium (bo), bothridial seta (bs), notogastral or gastronotal setae (c-, d-, l-, h-, p-series), exuviae of larva (L), protonymph (Pn) and deutonymph (Dn), lyrifissures or cupules (ia, im, ip, ih, ips, iad, ian), integumental pit (em), opisthonotal gland opening (gla), pedotectum (Pd), discidium (Dis), subcapitular setae (a, m, h), cheliceral setae (cha, chb), Trägårdh organ (Tg), palp setae (sup, inf, l, d, cm, acm, it, vt, ul, su) and solenidion ω, epimeral setae (1a–c, 2a, 3a–c, 4a–c), adanal and anal setae (ad-, an-series), aggenital (ag) and genital setae (g), leg solenidia (σ, 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 (1939, 1949, 1953) and Norton and Behan-Pelletier (2009). The species names follows Subías (2004, updated 2020).
Proteremaeus oralensis sp. nov.
(Figs. 1–15)
Diagnosis
Adult of medium size (507–572), with characters of Proteremaeus. Rostral and lamellar setae of medium size and finely barbed, interlamellar seta short and smooth. Lamellar costula long, s-shaped, with seta le and in in anterior and posterior part, respectively; transverse ridge present between anterior part of lamellar costula, and small triangular ridge between lamellar costula and bothridium. Bothridial seta clavate, with narrow, barbed head. Notogaster with reticulate pattern and 11 pairs of short setae, posterior tip of notogaster rounded. Adanal and anal setae with basal porose ring.
Juveniles oval, light-brown. Prodorsum without ridges in central part, and with short setae, but le longer than in. Bothridium rounded, bothridial seta clavate, with barbed head. Gastronotum with 12 pairs of short setae, nymphs quadrideficient and eupheredermous, carrying exuvial scalps of previous instars, most setae inserted in peripheral part of gastronotum. Posterior setae p1 and h1 inserted close to each other, seta h2 inserted approximately at similar distances from seta p1 and p2.
Morphology of adult
Measurements. Mean length (and range) of females 565.0±8.2 (553–572, n= 13) and males 525.8±10.9 (507–540, n= 17), mean width (and range) of females 352.0±8.7 (338–358) and males 307.2±22.8 (267–332).
Integument. Most parts of body with reticulate pattern, well observed on notogaster, lateral parts of prodorsum, tectopedia I and II and epimeres (Figs. 1, 2, 3a, 5, 6), and covered with granular cerotegument.
Prodorsum. Rostrum rounded, rostral seta of medium size (length 28–30), finely barbed, inserted on lateral part of rostrum (Figs. 1, 2, 3a, 5, 6a). Lamellar costula long, narrow (90–101 × 5), s-shaped, located on lateral part of prodorsum, with seta le and in in anterior and posterior part, respectively; small triangular ridge present between lamellar costula and bothridium. Lamellar seta slightly longer (33–35) than rostral seta (27–29), both with very short barbs, interlamellar seta short (12) and smooth. Two transverse ridges present, longer anterior to setal pair le and shorter between pair le. Bothridium rounded, bothridial seta (bs, 42–45) clavate, with narrow, flattened and barbed head (Figs. 1, 3a, 5, 6). Exobothridial seta (ex, 15) thin and smooth, inserted closer to pedotectum II than to bothridium. Integumental pit em present between seta ex and pedotectum II.
Notogaster. Longer (368–415) than wide (267–358), with 11 pairs of short setae (26–35). Lyrifissure ia posterolateral to seta c2, im posterior to seta la, ip posterolateral to seta h2, ips and ih anterolateral and anterior to seta p3, respectively, opisthonotal gland opening anterolateral to seta lp (Figs. 1, 2, 3a). Posterior tip of notogaster rounded.
Gnathosoma. Infracapitulum diarthric, subcapitular setae short (21–25) and barbed (Figs. 2, 7a). Apical part of palp (71) relatively wide, most setae relatively long and smooth, except for barbed tibial l'', solenidion ω separated from seta acm (Figs. 3b, 7a), formula of setae (trochanter to tarsus + solenidion ω): 0-2-1-3-9(1). Chelicera (122 x 55) chelate, seta cha longer (35) than chb (21), both barbed, barbs on cha clearly longer than on chb (Figs. 3c, 7a).
Ventral and lateral regions. Apodemes I, II and IV strongly developed and fused with sternal ridge, apodeme III short. Epimeral setae short (12–15) and smooth, formula of epimeral setae 3-1-3-3. Genital setae (6 pairs), aggenital setae (1 pair), adanal setae (3 pairs) and anal setae (2 pairs) as short as epimeral setae, adanal and anal setae with basal porose ring. Lyrifissure iad anteromedial to seta ad3, ian anterior to seta an2. Ovipositor long, with relatively short apical setae (Fig. 3a).
Legs. Trochanters III and IV and all femora flattened, with ventral carina and porose areas on paraxial side. Most leg setae finely barbed or smooth. Seta d present on all genua and tibia IV, close to proper solenidion (Fig. 4). Formulae of leg setae (and solenidia, trochanter to tarsus): I—1-5-4(1)-4(2)-20(2); II—1-5-4(1)-4(1)-15(2); III—2-3-2(1)-3(1)-15; IV—1-2-1-3(1)-12. Leg tarsi tridactylous.
Description of juveniles
Larva oval (Fig. 8), body light-brown. Prodorsum subtriangular, without distinct ridges in central part, and with short (Table 1) and smooth setae, ro and le longer than other setae. Mutual distance between setal pair le about two times longer than between pair ro, between setal pair in about four times longer than between pair ro, pair le inserted closer to pair ro than in. Opening of bothridium rounded, bothridial seta clavate, with barbed head. Transverse and inclined folds in medial and posterior part of prodorsum. Integumental pit em present posterolateral to seta ex (Fig. 10a).
Gastronotum of larva with 12 pairs of setae, including h3 inserted lateral to medial part of anal opening (Fig. 9a), all short (Table 1) and smooth. Gastronotum with transverse and inclined folds in anterior and medial parts, and longitudinal folds in lateral parts. Paraproctal valves (segment PS) with two pairs of small setae. Cupule ia posterolateral to seta c3, im posterior to seta lm, ip posterior to seta h2, ih lateral to anterior part of anal valves (Fig. 9a). Gland opening located lateral to seta h2. Anal region with transverse and inclined folds, lateral parts of gastronotum with longitudinal folds. Most leg setae smooth or finely barbed (Fig. 11), seta d present at solenidia on all genua, but thin, short and difficult to observe.
Protonymph more stocky (Fig. 9b) than larva, body light-brown. Prodorsum, prodorsal setae and bothridium as in larva, but bothridial seta with slimmer head than in larva. Gastronotum of protonymph with 12 pairs of setae because p-series appearing and remaining in deutonymph and tritonymph (Figs. 12a, 12b), and setae of d-series lost and remaining absent in all nymphs (Figs. 10b, 13), all short and most inserted in peripheral part of gastronotum. In protonymph, one pair of genital setae appearing on genital valves, and two pairs added in deutonymph and tritonymph each (Figs. 12a, 12b), all short and smooth. In deutonymph, one pair of aggenital setae and three pairs of adanal setae appearing, and remaining in tritonymph, all short and smooth. In protonymph and deutonymph, anal valves glabrous, in tritonymph two pairs of short and smooth anal setae present (Figs. 9b, 12a, 12b). All nymphs carrying exuvial scalps of previous instars on gastronotum (Figs. 7a–c, 10b, 13). After removal of these exuviae, dorsocentral part glabrous. In light microscope, prodorsum of tritonymph with transverse and inclined folds, in SEM micrographs with two longitudinal ridges and transverse ridges (Figs. 7b, 7c, 13). Setae p1 and h1 inserted close to each other, seta h2 inserted approximately at similar distances from seta p1 and p2 (Figs. 9b, 12a, 12b). Cupule ia and im located as in larva, cupule ip posterolateral (protonymph, deutonymph) or posterior to seta h2 (tritonymph), cupule iad lateral to anterior part of anal opening, cupule ips and ih displaced anterolateral and lateral from cupule iad, respectively, cupule ian anterior to seta an2, gland opening anterolateral to seta ad3 (Figs. 9b, 10b, 12, 14b–d). Anogenital region with transverse and inclined folds, lateral parts with longitudinal folds. Most leg setae smooth or finely barbed (Fig. 15), seta d present at solenidia on all genua and tibia IV, but thin, short and difficult to observe, at other solenidia on tibiae this seta not observed.
Summary of ontogenetic transformations
In all juveniles, the prodorsal setae are short, whereas in the adult ro and le are of medium size, and other setae are short. The bothridium is rounded in all instars, and the bothridial seta is clavate, but in the larva the head of the bothridial seta is relatively thicker than in the nymphs and adult. The larva has 12 pairs of gastronotal setae and so have the nymphs (p-series appears, d-series lost). The notogaster of the adult loses seta c3, such that and 11 pairs of setae remain. The formula of gastronotal setae in P. oralensis is 12-12-12-12-11 (larva to adult), the formulae of epimeral setae are: 3-1-2 (larva, including scaliform 1c), 3-1-2-1 (protonymph), 3-1-2-2 (deutonymph) and 3-1-3-3 (tritonymph and adult). The formula of genital setae is 1-3-5-6 (protonymph to adult), that of aggenital setae is 1-1-1 (deutonymph to adult), and the formula of segments PS–AN is 23333-0333-022. The ontogeny of leg setae and solenidia of P. oralensis is given in Table 2.
Ecology and biology
Proteremaeus oralensis was relatively abundant in moist elderberry litter (134 indiv./500cm3) near Dachi-Novostroyka village (West Kazakhstan). In this habitat, the juveniles dominated, constituting 53% of all individuals. The stage structure of this species was the following: 2 larvae, 7 protonymphs, 70 deutonymphs, 62 tritonymphs and 126 adults. In this population, the sex ratio (females to males) was 1:1.3, and only two females were gravid, carying 1 large egg each (290 × 132), which comprised 51% of the length of females.
Type material deposition
Holotype female and five paratypes (two females and three males) are deposited in the University Museum of Bergen, University of Bergen, Bergen, Norway.
Etymology
The species name follows the Kazakhstanis name Oral (Uralsk), in which surroundings this species was found.
TABLE 1.
Measurements of some morphological characters of juvenile stages and adult of Proteremaeus oralensis sp. nov., (mean measurements of 2–10 specimens in µm); Nd: not developed.
TABLE 2.
Ontogeny of leg setae (Roman letters) and solenidia (Greek letters) in Proteremaeus oralensis sp. nov.
Comparison of morphology of Proteremaeus oralensis sp. nov. with congeners and remarks
Based on the mean length of adults of Proteremaeus species, the largest is P. oralensis sp. nov., and smallest is P. punctulatus, while the body length of P. jonasi Piffl, 1965 is unknown (Table 3). In most species, the bothridial seta is clavate, but in P. chadaevae Golosova, 1983, P. elongatus (Rjabinin & Krivolutsky, 1975) and P. nebaikini Behan-Pelletier & Rjabinin, 1991 it is fusiform. Most species have the transverse ridge between lamellar setae, whereas in P. chadaevae, P. jonasi, P. macleani Behan-Pelletier, 1982 and P. punctulatus this ridge is absent. In most species, the posterior tip of notogaster is present, whereas in P. chadaevae, P. jonasi and P. nebaikini it is absent. In most species, the notogastral seta c1 is absent, but in P. macleani and P. oralensis this seta is present. These species also differ from one another by the shape of posterior part of lamellar costula and shape of some setae (Table 3).
The morphological ontogeny of P. oralensis is similar to that of P. punctulatus investigated by Seniczak et al. (2013). The larva of both species differs slightly from each other in the length of seta h1, but the tritonymph of P. oralensis differs clearly from that of P. punctulatus by the location of setae h1, h2 and p1 on the posterior part of gastronotum (Table 4). The adults of P. oralensis have 11 pairs of notogastral setae, including c1, which is lacking in P. punctulatus. These species differ from each other also by the body size and shape of prodorsal seta in (Table 4). By contrast, the morphology of P. oralensis and P. punctulatus differs clearly from that of Eueremaeus laticostulatus Bayartogtokh, 2003, which has six pairs of adanal setae in the deutonymph, tritonymph and adult and 5–6 pairs of anal setae in the tritonymph and adult. Similar number of adanal and anal setae as E. laticostulatus have other species of Eueremaeus Mihelčič, 1963 and Eremaeus C.L Koch, 1835 (Behan-Pelletier 1993, Seniczak et al. 2013, 2014), and in species with known ontogeny, the location of setae h1, h2, p1 and p2 on the gastronotum has diagnostic value, as in Proteremaeus species.
TABLE 3.
Selective morphological characters of Proteremaeus oralensis sp. nov., P. punctulatus and Eueremaeus laticostulatus.
The adults of Proteremaeus have 10 or 11 pairs of notogastral setae, depending on seta c1, which in P. oralensis and P. macleani is present, and in other species is absent. The number of c-series setae on the notogaster is an important character of Brachypylina (Circumdehiscence) that can explain the phylogeny of mites. According to Grandjean (1939, 1949, 1953) and Shaldybina (1972) during the phylogeny loss of notogastral setae starts with the c-series, but the former author thought that the first is lost seta c1, and next c3 and only c2 remains, whereas the latter author observed this loss in an opposite order, e.g. from c3 via c1 to c2. Proteremaeus oralensis and P. macleani lost one setae of cseries (c3), whereas other species lost two setae (c3 and c1), so the latter species are phylogenetically younger than P. oralensis and P. macleani. Proteremaeus loses setae of c-series according to Shaldybina (1972), similarly as Sphaerozetinae (Ceratozetidae) sensu Shaldybina (1975), where we can observe gradual loss of setae of c-series and d-series. For example, the most primitive Ghilarovizetes has 15 pairs of notogastral setae, and only f1 is lacking, comparing to holotrichous setal pattern of Hermannia Nicolet, 1855 (Seniczak et al. 2017a, b), whereas Melanozetes loses seta c1 and 14 pairs of notogastral setae remain (Shaldybina 1975; Seniczak et al. 1990, 2015). Fuscozetes loses also seta c3, and some species lose some or all setae of d-series, such as 10–13 pairs of notogastral setae remain, including c2 (Seniczak et al. 1990, 1991, 2016). However, the nymphs of Sphaerozetinae are apheredermous, and have 15 pairs of gastronotal setae, and this subfamily loses setae of d-series between the tritonymph and adult, whereas the nymphs of Proteremaeus are eupheredermous, and lose setae of d-series between the larva and protonymph. Loss of setae of dseries in this genus makes the central part of gastronotum glabrous, which allows carry the dorsal exuvial scalps of previous instars.
TABLE 4.
Selected morphological characters of Proteremaeus species; Ng: notogaster (notogastral).
Proteremaeus has seta d at some leg solenidia, but this seta is usually short and thin or closely associated with corresponding solenidion (Bayartogtokh 2000), and therefore it is difficult to observe in the light microscope. For example, in P. oralensis, seta d is present on genua I–III and tibia IV, but this observation is based on several specimens, and different angles of observations. In other species of Proteremaeus, this seta was noted either at all leg solenidia on genua and tibiae, at some of them or leg setae of species are unknown (Table 4). Therefore, the diagnostic value of coupled seta d in Proteremaeus seems to be small, which is consistent with the observation of Behan-Pelletier (1993), who investigated the presence of seta d at solenidia of 42 North American species of close related genera Eremaeus and Eueremaeus; in 10 species she found this seta, in seven species this seta was present or absent, and in other species it was absent.
Acknowledgements
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).