Verachthonius cf. laticeps (Strenzke, 1951)

Ordouni, Fatemeh, Ramroodi, Sara, Akrami, Mohammad Ali & Rakhshani, Ehsan, 2023, Oribatid mites (Acari: Oribatida) from southeastern Iran, with supplementary description of Verachthonius cf. laticeps (Brachychthoniidae), Persian Journal of Acarology 12 (2), pp. 173-188 : 181-186

Verachthonius cf. laticeps (Strenzke, 1951) ( Figs. 2–11 )

Supplementary description

Measurements (n = 3) – Body length 210–218 (length of prodorsum 65–68; length of notogaster 145–150: NA 53–54, NM 27–29, NP 65–67); width of prodorsum 82–84; width of notogaster 128–130. Lateral height 90–94. Bothridial seta (peduncle 20–22, head 19–20). Bothridium: diameter 13, length 10–11. Op 5 × 7.5. Prodorsal setae ro 18–19, le 17, il 16, exa 17. Notogastral setae c 1 17, c 2 16, c 3 16, d 1 18, d 2 16, d 3 18, e 1 15, e 2 19, f 1 18, f 2 17, h 1 18, h 2 16, h 3 15, p 1 15, p 2 13, p 3 15. Intervals of setae: ro -ro 10, le -le 23, il -il 30, exa -exa 66–67, c 1 - c 1 44, d 1 - d 1 38, e 1 - e 1 31, f 1 - f 1 14–15, h 1 - h 1 26–28, h 2 - h 2 53–55, p 1 - p 1 27. Epimeral setae 6–7. Anogenital setae pe 7–8, an 1 and an 2 9–10, ad 1 16, ad 2 14, ad 3 13, g 1-7 and ag 5–6. Chelicera 40. Cheliceral seta 10–11. Palp 50– 52. Subcapitulum 54–56 × 24–25. Subcapitular setae h and ma 7–8, m and a 9–10. Adoral seta or 10.

Integument – Body yellowish in color; integumental surface smooth, not sculptured. Cuticle of body smooth, not sculptured, only with numerous round or oval muscle sigillae on dorsal plates and legs.

Prodorsum ( Fig. 2 ) – Broader than long and slightly narrower than the notogaster. Rostrum widely rounded and rostral apex without teeth. Prodorsal setae thick, setiform and smooth, rostral seta (ro) larger setae, situated near tip of rostrum, close together and parallel to each other. Another three pairs of prodorsal setae (except bothridial seta) nearly equal in length, and smooth. Longitudinal, transversal and curved ridges visible between rostral, lamellar and exobothridial setae. Both lamellar (le) and interlamellar (il) setae slightly shorter than their mutual distance. Anterolaterad of each bothridium, a spherical, robust lateral tubercle (op) present; anterior exobothridial seta (exa) inserted on its anterior rim, nearly as long as other prodorsal setae (except ro); posterior exobothridial pore (exp) lateral to bothridium. Bothridium (bo) cup-shaped, with wide opening, directed posterolaterally. Bothridial seta (bs) spindle-shaped and barbed. One pair of mascle sigillae in the exobothridial regions and two pairs of oblong or oval-shape mascle sigillae in the between of interlamellar setae.

Notogaster ( Fig. 2 ) – Parallel-sided laterally, almost evenly rounded posteriorly with 16 pairs of medium long, stout and smooth setae. Setal row c and d (6 pairs) on anterior notogastral sclerite (NA), row e (2 pairs) on medial (NM), and rows f, h and p (8 pairs) on posterior sclerite (NP). Seta d 2 close to d 1, setae p 2 and p 3 visible in lateral and ventral view. NA bearing four mascle sigillae on each side, middle two mascle sigillae near each other; NM with three small mascle sigillae on each side and NP bearing two near and small spots on each side addition four large spots, touching each other between setae p1.

Pleural region ( Fig. 4 ) – Only one pair of suprapleural plate (SpE) present. Anterior pleural sclerite (PA) triangular, with weak ridges, anterior apex reaching close to region of lyrifissure ia. posterior pleural sclerite (PP) wider, smooth and fused to ended of NP. Sclerites PA and PP separated from each other. Lyrifissures (ia, im, ih, ip and ips) as small cupules, in usual position.

Gnathosoma ( Figs. 3 , 5–7 ) – Subcapitulum bearing subcapitular setae (a, ma, m and h), setae h and ma short and setae h longer than their mutual distance. Adoral setae (or) square-tipped and flated at apex. Rutellum (ru) tri-dentated directed anteromedial and bears two independent brushes (br) on its dorsal face, that one shorter than the other. Palp five-segmented with formula: 0-2-1-3- 10(+1ω), setae (u) fused, bifid; all setae smooth. Chelicerae weakly dentate, with one setiform and smooth seta (cha) on dorsum of fixed digit that directed anteriad. Movable digit small. Chelicera proximally inserted in body wall and adaxially emarginated; lamellated organ (l.or), oncophysis opʹ and the cheliceral frame attachment (line en) present.

tarsus) omitted; 6. Left palp, dorsoabaxial view; 7. Left chelicera, adaxial view. Scale bars 25 μm.

Epimeral region ( Fig. 3 ) – Epimeral setal formula: 3-1-3-4. All setae short, thin and almost equal in length.

Anogenital region ( Fig. 3 ) – Genital plates large, bearing seven pairs of short, smooth and thin setae (g 1- g 7) in two longitudinal rows (four medially and three laterally); one pair aggenital setae (ag) present on unsclerotized integument (aggenital sclerite absent). Peranal sclerites broad with one pair of peranal setae (pe). Ano-adanal sclerites with two pairs of equal, smooth and thin anal setae (an 1 -an 2); three pairs of long, thicker and smooth adanal setae (ad 1 -ad 3), progressively shorter from ad 1 to ad 3; adanal sclerites fused posteriorly, forming a U-shaped plate.

Legs ( Figs. 8–11 ) – All tarsi monodactylous; claws rather slender. Formulae of leg setation (solenidia): I: 0-3-3-4-18 (2-1-3), II: 0-4-3-4-14 (1-1-1), III: 2-3-3-3-11 (1-1-0), IV: 1-2-3-4-11 (1- 1-0); solenidion φ of tibia I and II very long; solenidia ω of tarsi I and II long, famulus ε of tarsus I short, inserted beside ω 1. Coupled setae and solenidia on genua and tibiae I–IV. Oval-shape mascle sigillae present on some segments. Homology of leg setae and solenidia as shown in Table 1.

Remarks

The genus Verachthonius was erected by Moritz (1976) and then fully defined by Lee (1982) based on a limited number of species. To date, six species are included in Verachthonius ( Subías 2022) that are closely related and some of which can be distinguished only with difficulty. One problem in classifying this genus is that the descriptions of some included species are too brief and mainly based on the dorsal view of body, thus more of differentiating characteristics were overlooked. Distinguishing characteristics are found in the combination of body dimensions; form, relative length and distance between of dorsal setae; form of sensillus; dorsal mascle sigillae and ridges.

We consider the Iranian specimens similar to Verachthonius moritzi ( Lee 1982: p. 343) , Verachthonius pseudolaticeps ( Subías 1977: p. 65) , Verachthonius congruus ( Moritz 1976: p. 164) , Verachthonius diversus ( Moritz 1976: p. 159) and Verachthonius montanus (Hummer 1952: p. 17 & 1958: p. 19).

Verachthonius moritzi is the smallest species of the genus (158) and beside possessing more notal ridges than the other 5 nominal species, differs by having conspicuously large and fine notal setae that some of which on tubercle (“ S 5 ”), adanal shields not posteriorly merged together, aggenital sclerite present and some difference in leg cheatotaxy (tibia and tarsus I; tibia II and IV).

Verachthonius pseudolaticeps is the largest species of the genus (255) and differs by having fine and setiform dorsal setae that narrow towards the end, setae on NP longer than other notal setae and size and form of mascle sigillae (3 between il, 2 on each side NA and 1 on each side NM and NP).

Verachthonius congruus differs by having the dorsal setae being long, thin, faintly curved and stand away from the body, the pleural sclerites (PP and PA) overlapping, the number and position of the mascle sigillae (5 on prodorsum & 4 on NA), the structure of the sensillus and the distance between dorsal setae.

Verachthonius diversus differs by having short, simple and stout the dorsal setae, separation the pleural sclerites (PP and PA), the number and position of the mascle sigillae (only 5 on prodorsum), short stalk and stout fusiform club the bothridium.

Although the original description of Verachthonius montanus is not very detailed, according to the illustrations, the overall body shape, form and size of sensillus, relative length and distance between of dorsal setae, it has similarities with Iranian specimens however differs by having relatively large body size (240 × 140), lanceolate dorsal setae, adanal shields not posteriorly merged together, the number and position of the mascle sigillae, two bends just behind the rostral setae and connect the lamellar setae with a curved line. Present and number of the suprapleural sclerites are characters heavily weighted in diagnosing the genus (Schatz 2021: p. 376). Hammer (1952: p. 17) states in his generic diagnosis of Verachthonius montanus that “ On the ventral side three of the four lateral plates characteristic of the genus are seen (to the left on the figure 5 a)”, which contradicts the characteristics of Verachthonius .

According to the original description of Verachthonius laticeps (Strenzke 1951: p. 240) and supplementary description of this species by Moritz (1976: p. 155), Iranian specimens show the most similarities with this palearectic species by having medium long and stout dorsal setae, same distance between the dorsal setae, adanal sclerites fused caudally and simple and thin the adanal setae. Also it seems that there are some morphological differences such as body size, absent transverse bulge arching in front of the bases of setae h2 and h3, and curved ridges in the middle of prodorsum in Iranian specimens.

The resolution of some ambiguities by examining type specimens or in some cases must wait for the collection of new samples from the type localities and the creation of a neotype. In conclusion, the following key can be used to identify adults of all known species of Verachthonius .

Figures

Figures 2–4. Verachthonius cf. laticeps (Strenzke, 1951) – 2. Dorsal view of body; 3. Ventral view of body (legs and distal palp segments not shown); 4. Lateral view of body (legs and palp not shown). Scale bar 50 μm.

Figures 5–7. Verachthonius cf. laticeps (Strenzke, 1951) – 5. Subcapitulum, ventral view, distal palp segments (genu-

Figures 8–11. Verachthonius cf. laticeps (Strenzke, 1951(– 8. Leg I, left, adaxial view; 9. Leg II, right, abaxial view; 10. Leg III, right, adaxial view; 11. Leg IV, right, adaxial view. Scale bar 25 μm.