Ermilov, Sergey G. ¹ ; Rybalov, Leonid B. ² and Sharapov, Denis V. ³

¹✉ Tyumen State University, Institute of Environmental and Agricultural Biology (X-BIO), Tyumen, Russia.
²Institute of Ecology and Evolution, Russian Academy of Sciences, Laboratory of Soil Zoology and General Entomology, Moscow, Russia.
³Tyumen State University, Institute of Environmental and Agricultural Biology (X-BIO), Tyumen, Russia.

2024 - Volume: 64 Issue: 2 pages: 525-541

Original research

Keywords

Abstract

Introduction

The oribatid mite genus Ethiovertex Mahunka, 1982 (Acari, Oribatida, Scutoverticidae) comprises 10 species, distributed throughout the Afrotropical, Neotropical, Oriental, and southern Palaearctic regions (Subías 2022, unpublished online version 2024).

Ethiovertex africanus (Evans, 1953) was described by Evans (1953) from Tanzania. Until now, this species has been known only from the type locality (Kilimanjaro, mountainous soil). The original description of the adult is brief and incomplete. In particular, it lacks certain details concerning the morphology of the lateral and ventral sides of the body, gnathosoma, and the morphology and setation of the legs; only figures of the dorsal side of the body and legs I and IV have been presented. Nonetheless, the species is easily identifiable due to a specific set of morphological characters: bothridial seta short, erect, with globular, barbed head; translamella present; the cusp of lamella with anteromedial triangular process; the humeral region of the notogaster narrowly depressed and bordered by long, oblique ridge.

In the course of a taxonomic survey of the Ethiopian mites collected from the Bale Mountains National Park, we found E. africanus represented by all ontogenetic instars. Prior to this study, the morphology of the juvenile instars of this species, as well as the morphology of juveniles within Ethiovertex were unknown (Norton and Ermilov 2014, 2024). In the family Scutoverticidae, juvenile morphology is known for 10 species (Norton and Ermilov 2014) from three genera (Arthrovertex Balogh, 1970 – one species; Provertex Mihelčič, 1959 – three species; Scutovertex Michael, 1879 – six species). Fernández and Cleva (2002) described a tritonymph of A. coineaui (Fernández and Cleva, 2002). Travé (1963, 1964) described all juvenile instars of P. delamarei Travé, 1963 and P. mailloli Travé, 1964, respectively. Pfingstl et al. (2008, 2009) described all juvenile instars of S. sculptus (Michael, 1879) and P. kuehnelti Mihelčič, 1959, respectively. Aoki (2000) presented a figure of a nymph of S. japonicus Aoki, 2000. Schäffer and Krisper (2007) described all juvenile instars of S. minutus (Koch, 1835). Ermilov et al. (2008) described all juvenile instars of S. neonominatus Subías, 2004 (as S. perforatus) and S. sculptus (Michael, 1879) (as S. rugosus). McCullough and Krisper (2013) described all juvenile instars of S. pannonicus Schuster, 1958. Finally, Ermilov and Chistyakov (2004) briefly described all juvenile instars of S. punctatus Sitnikova, 1975. Also, some morphological data were provided in Michael (1884), Grandjean (1949) and Haarløv (1957). The main juvenile traits of Scutoverticidae and Scutovertex were summarized by Grandjean (1953).

The main goal of this paper is to present a supplementary description of the adult E. africanus based on the material from Ethiopia and to summarize its diagnostic morphological traits, which will help with the identification of this and related species in the future. An additional goal is to describe the morphology of this species' juvenile instars.

Material and methods

Material — Sixty-four specimens (23 adults: five males and 18 females; 41 juvenile instars: 14 larvae, 10 protonymphs, 10 deutonymphs, and seven tritonymphs) were collected from the following locality (Fig. 1a): Ethiopia, Bale Mountains National Park, Sanetti Plateau, 6°53′14″ N; 39°54′24″ E, 3975 m a.s.l., rocky alpine communities, mosses on a stone lying along a spring, 6 November 2023 (L.B. Rybalov). All specimens have been preserved in 70% solution of ethanol with a drop of glycerol and stored in the collection of the Tyumen State University Museum of Zoology, Tyumen, Russia.

Sampling — Substrate samples (moss) containing oribatid mites were collected using a stainless-steel frame (50 × 50 cm) with a sieve (mesh size 2 × 2 cm). Mites were extracted into 75% ethanol using Berlese`s funnels with electric lamps in laboratory conditions (at the Institute of Ecology and Evolution, Moscow, Russia).

Juvenile specimens were associated with adults using criteria outlined by Norton and Ermilov (2014). In particular, they were found in the same samples with the adults and had appropriate size and proportions.

Observation and documentation — For measurements and illustrations, specimens were mounted in lactic acid on temporary cavity slides. Some specimens were preliminarily placed for one day in a concentrated (5%) potassium hydroxide solution to illuminate their body surface and to dissolve the cerotegument. All body measurements are presented in micrometers (µm); body length was measured in lateral view, from the tip of the rostrum to the posterior edge of the gastronotum; notogaster/gastronotic width refers to the maximum width of the notogaster/gastronotic region in dorsal view; the lengths of body setae were measured in lateral aspect. Formulas for leg setation are given in parentheses according to the sequence trochanter-femur-genu-tibia-tarsus (famulus included); formulas for leg solenidia are given in square brackets, according to the sequence genu-tibia-tarsus. Drawings were made with a camera lucida using a Leica transmission light microscope Leica DM 2500. Images were obtained with an AxioCam ICc3 camera using a Carl Zeiss transmission light microscope Axio Lab.A. Image stacks were combined using the Helicon Focus Pro (v. 5.0) suite. For SEM microscopy, alcohol-preserved mites were covered with gold and scanned with the aid of a TESCAN Mira3 LMU SEM microscope.

Terminology — Morphological terminology used in this paper mostly follows that used in the papers on Scutoverticidae (e.g., Ermilov et al. 2008, 2023); also, see Norton (1977) for leg setal nomenclature and Norton and Behan-Pelletier (2009) for overview.

Abbreviations — Prodorsum: lam = lamella; tlam = translamella; dlc = lateral carina; tc = transverse carina; lpl = lateral prodorsal ledge; ro, le, in, bs, ex = rostral, lamellar, interlamellar, bothridial, and exobothridial setae, respectively; D = dorsophragma. Notogaster/Gastronotic region: c, da, la, dm, lm, dp, lp, h, p = setae; ia, im, ip, ih, ips = lyrifissures/cupules; gla = opisthonotal gland opening. Gnathosoma: a, m, h = subcapitular setae; or = adoral seta; d, l, v, cm, acm, ul, su, vt, lt = palp setae; ω = palp solenidion; cha, chb = cheliceral setae; Tg = Trägårdh's organ. Epimeral and lateral podosomal regions: er = epimeral ridge; 1a, 1b, 1c, 2a, 3a, 3b, 4a, 4b = epimeral setae; Cl = Claparède's organ. Anogenital region: g, ag, an, ad = genital, aggenital, anal, and adanal setae, respectively; iad = adanal lyrifissure/cupule. Legs: Tr, Fe, Ge, Ti, Ta = trochanter, femur, genu, tibia, and tarsus, respectively; ω, φ, σ = solenidia; d, l, v, bv, ev, ft, tc, p, u, a, s, pv, pl = setae; sac = saccule; bra = brachytrachea. Instars: LA = larva, PN = protonymph, DN = deutonymph, TN = tritonymph, JUV = juvenile instars; AD = adult.

Descriptions

Ethiovertex africanus (Evans, 1953)

(Figures 1–11)

Supplementary description of adult — Measurements – Body length: 570–615 (males), 600–660 (females); notogaster width: 330–360 (males), 345–390 (females).

Integument (Figs 1b, 3c, 9a–d, 10a) – Body dark brown. Surface of body and legs slightly densely microtuberculate (well visible in dissected specimens under high magnification, ×1000), covered by thin layer of blocky cerotegument including dense microgranulate components and dirt; cerotegumental microgranules frequently forming club-shaped and ridge-like structures; interlamellar region with two slightly oblique ridges and some mediobasal ridges; humeral region of notogaster narrowly depressed and bordered by long, oblique ridge; dorsal part of notogaster with indistinct ridges and depressions in light microscope, but well observable in SEM; medioposterior part of subcapitular mentum with some transverse and oblique ridges; lateral side of body and ventral plate with some ridges.

Prodorsum (Figs 1b, 2a, c, 3b, 9a–d, 10a) – Rostrum broadly rounded (but it seems truncated in dorsal aspect), forming rostral ''visor″. Lamella about 2/3 length of prodorsum, with long (about 1/2 length of lamella), broad cusp having anteromedial triangular process (but sometimes it seems rounded in dorsal aspect); translamella present, thin. Rostral (41–49) and lamellar (52–60) setae rod-like, roughened, curved; bothridial seta (41–49) erect, with short stalk and globular, barbed head; stalk and head slightly differing in length; interlamellar and exobothridial setae and their alveoli absent.

Notogaster (Figs 1b, 2a, c, 3a, 9a–d) – Anterior margin distinct, convex medially. Humeral process broadly rounded, slightly developed. Lenticulus not observable. Ten pairs of notogastral setae (11–15) spiniform, roughened. Opisthonotal gland opening and all lyrifissures well visible.

Gnathosoma (Figs 2b, 3c–f) – Subcapitulum size: 142–150 × 94–105; mentum with anterior tectum; setae (a, h 26–34; m 30–37) rod-like, roughened; a and m slightly curved, h straight; both adoral setae (22) rod-like, roughened. Palp length 94–101; postpalpal seta (5) spiniform, smooth. Chelicera length 146–154; setae (cha 37–39; chb 34–37) setiform, barbed.

Epimeral and lateral podosomal regions (Figs 2b, c, 9c, d) – Epimeral setal formula: 3–1–2–2; all setae (3b 17–22; others 11–15) spiniform, roughened.

Anogenital region (Figs 2b, c, 3a, 9c, d) – Anogenital formula: 6–1–2–3; genital, aggenital, anal, and adanal setae (g₁ 22–30; others 13–17) spiniform, roughened. Adanal lyrifissure distinct.

Legs (Figs 4a–d, 9c, d, 10a) – Median claw thick, lateral claws thin, all slightly barbed on dorsal side. Femora I and II with dorsolateral (paraxial) brachytrachea; trochanters III, IV with dorsolateral (paraxial), femora III, IV with dorsolateral (paraxial) and tibiae I–IV with distoventral saccule. Femora II–IV with ventral ridge; femora III, IV, tibiae I–IV and tarsi I–IV with dorsal ridge; genua I–IV with lateral (antiaxial) ridge. Formulas of leg setation and solenidia: I (1–4–3–4–15) [1–2–2], II (1–4–3–4–13) [1–1–2], III (2–3–1–3–13) [1–1–0], IV (1–2–2–3–12) [0–1–0]; homology of setae and solenidia indicated in Table 1; solenidia φ₁ of tibia I and φ on tibia II long, subflagellate; other solenidia short, rod-like; seta s of tarsus I thorn-like, roughened (not eupathidial), located between paired setae a and pv; setae it′ and it″ absent on all tarsi.

Description of juvenile instars — Measurements – Total length of: larva 270–300, protonymph 360–420, deutonymph 435–495, tritonymph 525–545. Total width of: larva 150–165, protonymph 194–225, deutonymph 240–270, tritonymph 330–360.

Integument (Figs 1c, 5a–d, 6a–g, 10b–d, 11a) – Body colorless or grayish to light brown. Surface of body indistinctly porose (visible under high magnification in dissected specimens), partially covered by thin layer of dense microgranulate cerotegument; additionally, gastronotum, anogenital and epimeral regions folded.

Prodorsum (Figs 1c, 5a–d, 6e–g, 10c, d, 11b, c) – Relatively short, about 1/2 (in larva) or 1/3 (in nymphal instars) length of gastronotic region. Rostrum broadly rounded (illusorily seems truncated in dorsal aspect). Prodorsum with lateral ledge in larva. Dorsal side of prodorsum with one pair of dorsolateral carinae fused by transverse carina (most likely, being vestigial lamellae and translamella); basal part with semi-quadrangular ridge-like structure. Rostral seta (LA, PN 22–26; DN 26–30; TN 30–34) setiform, slightly barbed, inserted on small tubercle; lamellar, interlamellar and exobothridial setae (LA, PN 7–11; DN 7–11; TN 13–15) spiniform, roughened; bothridial seta (LA, PN 30–34, DN 30–37, TN 34–41) erect, with short stalk and globular, barbed head; stalk shorter than head.

Gastronotic region (Figs 1c, 5a–g, 6a–g, 10c, d, 11d–g) – Larva with 12, nymphal instars with 15 pairs of spiniform (except setiform, erect, slightly barbed h₂ in LA; some setae modified, with cylindrical mediobasal part and needleform distal part), roughened setae. Lengths of gastronotic setae: LA: h₂ 19–26, others 9–15; PN, DN 11–15; TN 15–19. Opisthonotal gland opening and all cupules (except ip not observable) poorly visible.

Gnathosoma (Figs 5h–j) – Subcapitulum size: LA 56–64 × 64–67, PN 75–82 × 75–82, DN 90–97 × 90–97, TN 109–116 × 109–116; anterior part of mentum with transverse ridge; length of subcapitular setae a, m: LA 15–19; PN, DN 15; TN 22; length of subcapitular seta h: LA 11–15, PN 11, DN 11–15, TN 15–19; length of adoral seta: LA 7–11; PN, DN 7; TN 11; a, m and adoral setae setiform, slightly barbed; h with cylindrical mediobasal part and needleform distal part. Palp length: LA 56–67; PN 64–71; DN 67–75; TN 79–82; palp formula in all instars: 0–2–1–3–9(+ω); solenidion distally connected with tubercle bearing eupathidium; length of postpalpal seta: LA, PN, DN, TN 7; seta spiniform, roughened. Chelicera length: LA 64–67, PN 82–86, DN 97–105, TN 120–131; length of setae cha and chb: LA 19–22; PN, DN 22–26; TN 26–30; length of seta chb: LA 15, PN 19, DN 20–22, TN 26; both setae setiform, barbed.

Epimeral and lateral podosomal regions (Figs 6a–g) – Setal formulas for epimeres: LA 3–1–2 (1c as typical scale covering Claparède's organ); PN 3–1–2–1; DN, TN 3–1–2–2; length of setae: LA, PN, DN 9–13; TN 15–19; all setae spiniform, roughened (sometimes some setae modified, represented by cylindrical mediobasal part and needleform distal part).

Anogenital region (Figs 6a–e) – Ontogeny of genital, aggenital, anal, and adanal setal formulas, larva to tritonymph: 0–1–3–5, 0–0–1–1, 0–0–0–2, 0–0–2–2, respectively; all setae (PN, DN 9–13, TN 15–19) spiniform, roughened; paraproctal setae absent. Adanal cupule distinct; anal cupule not observable.

Legs (Figs 7a–d, 8a–d, 10c, d, 11h, i) – Claw of each leg slightly barbed on dorsal side. Femora I–IV with distoventral saccule. Formulas of leg setation and solenidia: larva I (0–2–3–4–16) [1–1–1], II (0–2–3–3–13) [1–1–1], III (0–2–2–2–13) [1–1–0]; protonymph I (0–2–3–4–16) [1–1–2], II (0–2–3–3–13) [1–1–1], III (0–2–2–2–13) [1–1–0], IV (0–0–0–0–7) [0–0–0]; deutonymph I (0–4–3–4–16) [1–2–2], II (0–4–3–4–13) [1–1–2], III (1–3–2–3–13) [1–1–0], IV (0–2–2–2–12) [0–1–0]; tritonymph I (1–4–4–5–16) [1–2–2], II (1–4–4–5–13) [1–1–2], III (2–3–2–4–13) [1–1–0], IV (1–2–2–4–12) [0–1–0]; homologies of setae and solenidia indicated in Table 1.

General remarks

Comparison to the original description — The adult of E. africanus from Ethiopia is morphologically similar to that originally described from Tanzania (Evans 1953), but slightly smaller (570–660 × 330–390 versus 650–670 × 400–420). We believe this size difference represents an intraspecific variability, and therefore, it should be accounted for when identifying E. africanus in the future.

Diagnosis of adult E. africanus — Based on our supplementary description and on the original description of adult E. africanus (see Evans 1953), we propose the following diagnostic morphological traits for this species: body length 570–670; surface of body and legs slightly densely microtuberculate, covered by thin layer of blocky cerotegument including dense microgranulate components (cerotegumental microgranules frequently forming club-shaped and ridge-like structures); interlamellar region with two slightly oblique ridges; humeral region of notogaster narrowly depressed and bordered by long, oblique ridge; dorsal part of notogaster with indistinct ridges and depressions; rostrum rounded, forming rostral ''visor″; lamella with well-developed cusp having anteromedial triangular process; translamella present; rostral and lamellar setae medium-sized, rod-like, roughened; bothridial seta medium-sized, erect, with short stalk and globular, barbed head; humeral process present, broadly rounded; lenticulus not observable; notogastral setae short, spiniform, roughened; epimeral and anogenital setae short, spiniform, roughened; leg trochanters III, IV, femora I–IV and tibiae I–IV with saccule; setae it′ and it″ absent on all tarsi.

Main ontogenetic transformations of E. africanus — Measurements – Body size increases with each successive instar; length from 270–300 in LA to 570–660 in AD. Integument – Body colorless or light yellowish in JUV to dark brown in AD. In JUV, surface of body indistinctly porose, partially covered by thin layer of dense microgranulate cerotegument; additionally, gastronotum, anogenital and epimeral regions folded. In AD, surface of body microtuberculate, covered by thin layer of blocky cerotegument including dense microgranulate components and dirt (cerotegumental microgranules frequently forming club-shaped and ridge-like structures); interlamellar region with two slightly oblique ridges and some mediobasal ridges; humeral region of notogaster narrowly depressed and bordered by long, oblique ridge; dorsal part of notogaster with indistinct ridges and depressions; medioposterior part of subcapitular mentum with some transverse and oblique ridges. Prodorsum – In JUV, rostrum broadly rounded, with lateral ledge in LA. In AD, rostrum forming rostral peak. In JUV, dorsal side of prodorsum with one pair of dorsolateral carinae fused by transverse carina; basal part with semi-quadrangular ridge-like structure. In AD, prodorsum with well-developed lamellae with long, broad cusp having anteromedial triangular process; translamella present, thin. In JUV, rostral seta short, setiform, slightly barbed versus rostral seta medium-sized rod-like, roughened in AD; in JUV, lamellar, interlamellar and exobothridial setae short, spiniform, roughened versus lamellar seta medium-sized rod-like, roughened, interlamellar and exobothridial setae absent in AD; in all instars, bothridial seta comparatively short, erect, with short stalk and globular, barbed head. Notogaster/gastronotic region – In JUV, soft, slightly flattened versus hard, convex in AD. LA with 12, nymphal instars with 15, AD with 10 pairs of short, spiniform (except setiform h₂ in LA), roughened setae; in JUV, some setae modified, represented by cylindrical mediobasal part and needleform distal part. Gnathosoma – Subcapitulum with three pairs of subcapitular and two pairs of adoral setae in all instars. In JUV, anterior part of mentum with transverse ridge; setae a, m and adoral setae setiform, slightly barbed; h with cylindrical mediobasal part and needleform distal part versus mentum with anterior tectum; setae a, m and adoral setae rod-like, roughened. In all instars, palp formula 0–2–1–3–9(+ω); chelicera chelate-dentate, with two setiform, barbed setae. Epimeral and lateral podosomal regions – LA with six (1a, 1b, 1c as scale covering Claparède's organ, 2a, 3a, 3b), PN with seven (4a added), DN (4b added), TN and AD with eight pairs of epimeral setae; all setae short, spiniform, roughened (in JUV, some setae modified, represented by a cylindrical mediobasal part and a needleform distal part). In AD, pedotecta I, II well developed. Anogenital region – In PN, one pair of genital setae; in DN, two pairs of genital, one pair of aggenital and three pairs of adanal setae added; in TN, two pairs of genital and two pairs of anal setae added; in AD, one pair of genital setae added; all anogenital setae short, spiniform, roughened. Legs – In JUV leg tarsi with one claw versus with three claws in AD; leg setation increases from instar to instar as shown in Table 1.

Comparison of juvenile instars — Data on the juvenile morphology of Scutoverticidae are available for 10 species belonging to three genera (Arthrovertex, Provertex and Scutovertex). Morphological analysis shows a general similarity between juvenile instars of different species within the family (e.g., all scutoverticid juveniles with folded surface of gastronotum and ventral side; frequently short, spiniform gastronotic, epimeral and anogenital setae; epimeral and anogenital setation). Nonetheless, some differences between E. africanus and the other species can be observed.

The tritonymph of E. africanus differs from that of A. coineaui (see Fernández and Cleva 2002) in the length and morphology of lamellar and gastronotic setae c₂, c₃, la, lm, lp, h₁, h₂, h₃, p₁ (short, spiniform versus medium-sized, setiform).

Juvenile instars of E. africanus, P. delamarei (see Travé 1963), P. mailloli (see Travé 1964), and S. neonominatus (see Ermilov et al. 2008) are very similar, except the tritonymph of E. africanus without setae it′ and it″ on leg tarsi I–III (versus with these setae present in P. delamarei and P. mailloli).

Juvenile instars of E. africanus differ from those of P. kuehnelti (see Pfingstl et al. 2009) in the morphology of the gastronotic setae dm, dp, lp, h₁ (in larva); dp, lp, h₁, h₂, h₃ (in protonymph); dp, lp, h₁, h₂, h₃, p₁ (in deutonymph); and dp, lp, h₁, h₂, h₃, p₁, p₂, p₃ (in deuto- and tritonymph) (spiniform versus dilated distally in P. kuehnelti). Juvenile instars of E. africanus also differ in the absence (versus presence in P. kuehnelti) of setae it′ and it″ on leg tarsi I–III in tritonymph.

Juvenile instars of E. africanus differ from those of S. minutus (see Schäffer and Krisper 2007), S. pannonicus (see McCullough and Krisper 2013), and S. sculptus (see Ermilov et al. 2008; Pfingstl et al. 2008) in the length and morphology of bothridial seta (short, with globose head versus long, with elongate clavate head in S. sculptus) and in the absence (versus presence in S. sculptus) of setae it′ and it″ on leg tarsi I–III in tritonymph.

The published photograph of a nymphal instar of S. japonicus (see Aoki 2000) is of poor quality, and the description of juvenile instars of S. punctatus (see Ermilov and Chistyakov 2004) is brief. For these reasons, their morphological comparison with the juveniles of E. africanus is difficult.

Acknowledgements

We thank Dr. Gezahegn Degefe for supporting our field studies and organizing laboratory work. We also express gratitude to two anonymous reviewers for valuable comments and Nikita A. Shulaev for SEM micrographs. The work was performed within the framework of the Joint Russian-Ethiopian Biological Expedition, financially supported by the Russian Academy of Sciences. The collection of materials was conducted under the Agreement between the Russian Academy of Sciences and the Ministry of Science and Technology (Ministry of Innovation and Technology) of the Federal Democratic Republic of Ethiopia (17 Dec. 2020 – present).

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