Ontogenetic instars of Melanozetes paramollicomus sp. nov., with remarks on morphological ontogeny of Sphaerozetinae (Acari: Oribatida: Ceratozetidae) Author Bayartogtokh, Badamdorj 0000-0002-6370-5759 Department of Biology, School of Arts and Sciences, National University of Mongolia, Ulaanbaatar, Mongolia. bayartogtokh @ num. edu. mn; https: // orcid. org / 0000 - 0002 - 6370 - 5759 bayartogtokh@num.edu.mn Author Ermilov, Sergey G. 0000-0002-0913-131X Institute of Environmental and Agricultural Biology (X-BIO), Tyumen State University, Tyumen, Russia. ermilovacari @ yandex. ru; https: // orcid. org / 0000 - 0002 - 0913 - 131 X ermilovacari@yandex.ru Author Shtanchaeva, Umukusum Ya. Complutense University, Madrid, Spain. Author Subías, Luis S. Complutense University, Madrid, Spain. text Zootaxa 2021 2021-12-30 5086 1 69 89 journal article 2823 10.11646/zootaxa.5086.1.7 94248568-cae7-461f-a300-7f3584527910 1175-5326 5814499 C7E49DCD-114C-4E33-B854-94C9FB37FB4E Melanozetes paramollicomus sp. nov. Diagnosis. Adult . Body size: 830–913 × 581–630. Notogaster and ventral side of body sparsely foveolate. Rostrum weakly bulged with some stria. Basal part of pedotectum II and dorsal side of tutorium densely striate. Lamellar cusp truncate. Translamella present, often poorly visible. Rostral seta setiform, barbed (its basal part not covered by tutorial cusp); lamellar and interlamellar setae rod-like, slightly barbed; ro shortest, in longest. Bothridial seta of medium length, clavate Notogastral porose area Aa oval; A1 , A2 , A3 rounded, comparatively small. Fourteen pairs of notogastral setae ( c 1 absent) comparatively long, rod-like, slightly barbed ( c 3 slightly longer than others). Epimeral setae setiform, slightly barbed. Anogenital setae rod-like, slightly barbed; adanal setae longer than others, ad 3 ˃ ad 2 ˃ ad 1 ). All tibiae and genua with thick lateral antiaxial seta. Juvenile instars . Basal part of prodorsum and anterior part of gastronotum densely tuberculate; gastronotic shield (macrosclerite) and partially anogenital region sparsely foveolate. Rostral and interlamellar setae setiform, lamellar and exobothridial setae rod-like, all slightly barbed; in longest. Bothridial seta clavate, slightly barbed. Gastronotic setae rod-like, slightly barbed; c 2 , c 3 , dp longest in larva and protonymph, c 2 , c 3 , dp , h 1 —in deutonymph, c 3 —in tritonymph. Epimeral setal formula of deutonymph: 3-1-3-2. Epimeral and anogenital setae setiform, slightly barbed. FIGURE 2. Melanozetes paramollicomus sp. nov. , adult:A—lateral view (legs not shown); B—posterior view; C—subcapitulum, ventral view; D—right lip with adoral setae, ventral view; E—palp, left, antiaxial view; F—chelicera, right, antiaxial view; G—ovipositor. Scale bars 100 μm (A, B), 50 μm (C, D, F, G), 20 μm (E). Adult ( Figs 1–4 , 5A ) Measurements . Body length: 879 ( holotype , female), 830–913 ( 31 paratypes , 18 males and 13 females ); notogastral width: 614 ( holotype ), 581–630 ( 31 paratypes ). Females larger than males: 879–913 × 614–630 versus 830–863 × 581–597. Integument ( Figs 4A, 4B ). Body colour brown. Body covered by thin layer of gel-like cerotegument with microgranular inclusions. Body surface and legs densely microporose (visible only under high magnification in dissected specimens); additionally, notogaster, subcapitular mentum and gena, antiaxial side of leg femora I-IV and trochanters III, IV, and ventral side of body sparsely foveolate (diameter of foveola up to 2). Rostrum nearly bulge with some stria. Basal part of pedotectum II and dorsal side of tutorium densely striate. FIGURE 3. Melanozetes paramollicomus sp. nov. , adult: A—leg I, right, antiaxial view; B—leg II, right, antiaxial view; C—leg III, left, antiaxial view; D—leg IV, left, antiaxial view. Scale bar 50 μm. FIGURE 4. Melanozetes paramollicomus sp. nov. , adult, SEM micrographs:A—dorsal view; B—ventral view C—dorsoanterior view; D—dorsoposterior view. Scale bar 200 μm. Prodorsum ( Figs 1A , 2A , 4A, 4C , 5A ). Rostrum broadly rounded. Anterior part of prodorsum (near rostrum) with slight bulge. Lamella (including cusp) about 3/5 length of prodorsum; cusp short, truncate. Translamella short, thickened, often poorly visible. Tutorium (including cusp) about 2/3 length of prodorsum; cusp short, triangular. Lateral porose areas oval, poorly visible, located above basal part of tutorium. Genal tooth elongate triangular. Rostral seta (118–123) setiform, barbed; its basal part not covered by tutorium. Lamellar (139–151) and interlamellar (241–255, sometimes up to 287) setae rod-like, slightly barbed. Bothridial seta (69–77) clavate (illusory may seem globular in dorsal view), slightly barbed; stalk and head approximately equal in length. Exobothridial seta (65–77) setiform, slightly barbed. Dorsosejugal porose area oval, poorly visible. Dorsophragmata located close to each other, connected apically. Notogaster ( Figs 1A , 2A, 2B , 4A, 4D , 5A ). Lenticulus large, with diffuse borders. Pteromorph broadly rounded laterally. Four pairs of porose areas, Aa oval (28–32 × 20–28) others rounded (12–20). Fourteen pairs of notogastral setae ( c 1 absent) comparatively long ( c 3 : 164–180; others: 143–164), rod-like, slightly barbed. Opisthonotal gland opening and all lyrifissures distinct. Gnathosoma ( Figs 2C–2F ). Subcapitulum longer than wide (209–229 × 164–172). Subcapitular setae setiform, a (32–41) and m (61–69) slightly barbed, h (82–94) barbed. Adoral seta (20–24) setiform, barbed. Palp (131–135) with typical setation: 0–2–1–3–9(+ω). Postpalpal seta (6) spiniform. Axillary saccule (20–28) distinct, oblong. Chelicera (221–229) with two setiform, barbed setae ( cha : 90–98; chb : 41–45). Lateral podosomal and epimeral regions ( Figs 1B , 2A , 4B , 5A ). Humeral porose areas Am and Ah elongate oval, poorly visible. Custodium short, narrowly triangular. Discidium broadly triangular. Circumpedal carina long, apically fused to custodium. Horizontal folds in the integument between and dorsal of acetabula II and III not observed. Epimeral setal formula: 3–1–3–3. Epimeral setae ( 1b , 3c : 77–86; 1c , 3b , 4a : 49–61; others: 32–45) setiform, slightly barbed. Anogenital region ( Figs 1B , 2A, 2B, 2G , 4B , 5A ). Six pairs of genital (41–45), one pair of aggenital (41–45), two pairs of anal (57–65) and three pairs of adanal ( ad 1 : 102–131; ad 2 : 90–110; ad 3 : 57–65) setae rod-like, slightly barbed. Adanal lyrifissure located close and parallel to anal plate. Postanal porose area (65–73 × 8–10) elongate oval. Ovipositor elongated (269–274 × 123–131), blades (106–114) shorter than length of distal section (beyond middle fold; 155–168). Setae ψ 1 and τ 1 (57–65) rod-like; ψ 2 , τ a , τ b , τ c (26–28), and k (22–24) thorn-like. Legs ( Figs 3A–3D ). Median claw distinctly thicker than lateral claws, all slightly barbed dorsally. Dorsoparaxial porose area on femora I-IV and on trochanters III, IV large, distinct. Proximoventral porose area on tarsi I-IV and distoventral porose area on tibiae I-IV small, poorly visible. Genua I-IV without triangular process. Formulas of leg setation and solenidia: I (1-5-3-4-18) [1-2-2], II (1-5-3-4-15) [1-1-2], III (2-3-1-3-15) [1-1-0], IV (1-2-2-3-12) [0-1- 0]; homology of setae and solenidia as indicated in Table 1 . Famulus short, mini-stick, slightly curved and swollen distally, inserted laterally to solenidion ω 1 . Seta s on tarsus I eupathidial, located before setae a’ and a” . Setae v’ and l” on tarsus I absent. All tibiae and genua with thick lateral antiaxial seta. Solenidion ω 1 and ω 2 on tarsus II and σ on genu III rod-like, other solenidia setiform. Juvenile instars ( Figs 5B–5E , 6–9 ) Measurements . Total length of larva: 332–381 (n=6), protonymph: 431–464 (n=5), deutonymph: 531–597 (n=5), tritonymph: 630–747 (n=6). Total width of larva: 249–282 (n=6), protonymph: 298–348 (n=5), deutonymph: 381– 415 (n=5), tritonymph: 448–481 (n=6). Integument ( Figs 5 B-5E). Body pale yellow to light brown. Cuticle densely and partially microsculpturing and microporose. Basal part of prodorsum and anterior part of gastronotum densely tuberculate. Gastronotic shield (macrosclerite) and partially anogenital region sparsely foveolate. Anogenital region and lateral side of body with some folds. Sternal epimeral region with some folds and tubercles. Prodorsum ( Figs 5 B-5E, 6A, 6C, 7A, 7C). Relatively about 2/3 length of gastronotic region. Rostrum rounded. Rostral and interlamellar setae setiform, lamellar and exobothridial setae rod-like, all slightly barbed. Bothridial seta clavate, slightly barbed; stalk longer than head. Prodorsal setae lengths during ontogeny are presented in Table 2 . Transverse ridge slightly developed between interlamellar setae. Gastronotic region ( Figs 5B, 5C , 6 A-6C, 7A-7C, 8D, 8E). Humeral elongate sclerite and gastronotic shield (macrosclerite) distinct. Humeral organ present, positioned anterolateral to seta c 3 . Larva with 12 pairs (of these, seven pairs located on macrosclerite), nymphs with 15 pairs (of these, 10 pairs located on macrosclerite) of rod-like, slightly barbed setae. Gastronotic setae lengths during ontogeny are presented in Table 2 . Cupules ia , im and ip and opisthonotal gland opening well visible. Gnathosoma ( Fig. 8A ). Generally similar to adult except the following characters: labiogenal articulation of subcapitulum not observed; subcapitular setae equal in length, all slightly barbed. Epimeral region ( Figs 5C , 6B, 6C , 7B, 7C , 8B, 8C ). Setal formulas for successive epimeres: larva 3-1-2 (third setae of first epimere forms protective scale over respective Claparède’s organs); protonymph 3-1-2-1; deutonymph 3-1-3-2, tritonymph 3-1-3-3. Setae setiform, slightly barbed. Epimeral setae lengths during ontogeny are presented in Table 2 . Anogenital region ( Figs 5C , 6B, 6C , 7B, 7C , 8D, 8E ). Ontogeny of genital, aggenital, adanal, anal setal formulas, larva to tritonymph: 0-1-3-5, 0-0-1-1, 0-0-3-3, 0-0-0-2, respectively. All setae setiform, slightly barbed. Cupules ih , ips , iad appearing in normal ontogenetic pattern. Anogenital setae lengths during ontogeny are presented in Table 2 . Legs ( Figs 9 A-D). Claw of each leg strong, slightly serrate dorsally. Ventroparaxial porose area on femora I-IV and on trochanters III, IV large, distinct. Proximoventral porose area on tarsi I-IV and distoventral porose area on tibiae I-IV not observed. Leg formulas: larva: I (0–2–2–3–16) [1–1–1], II (0–2–2–2–13) [1–1–1], III (0–2–1–1–13) [1–1–0]; protonymph: I (0–2–2–3–16) [1–1–2], II (0–2–2–2–13) [1–1–1], III (0–2–1–1–13) [1–1–0], IV (0–0–0– 0–7) [0–0–0]; deutonymph: I (0–4–2–3–16) [1–2–2], II (0–4–2–3–13) [1–1–2], III (1[or 2]–3–1–2–13) [1–1–0], IV (0–2–2–1–12) [0–1–0]; tritonymph: I (1–4–3–4–18) [1–2–2], II (1–4–3–4–15) [1–1–2], III (2–3–1–3–15) [1–1–0], IV (1–2–2–3–12) [0–1–0]. Homologies of leg setae and solenidia as indicated in Table 1 . Material examined. Holotype ( female ), 31 paratypes ( 18 males , 13 females ) and 22 juvenile instars ( six larvae , five protonymphs, five deutonymphs, six tritonymphs): Ethiopia , Amhara Region , Debre Berhan , 10.29408ºN ; 039.90089ºE , 2890 m a.s.l., litter in Juniperus forest, 17.03.2020 (collected by L.B. Rybalov ). FIGURE 5. Melanozetes paramollicomus sp. nov. , adult (A) and deutonymph (B–E), SEM micrographs: A, C—lateral view; B—dorsal view D—dorsoanterior view; E—bothridium, bothridial and exobothridial setae. Scale bars 200 μm (A–D), 20 μm (E). TABLE 1. Development of leg setation of Melanozetes paramollicomus sp. nov.

Tr	Fe	Ge	Ti	Ta
Leg I
La	–	d , bv”	(l) , σ	(l) , v’ , φ1	(ft) , (tc) , (p) , (u) , (a) , s , (pv) , (pl), ɛ, ω1
Pn	–	–	–	–	ω2
Dn	–	(l)	–	φ2	–
Tn	v’	–	v’	v”	(it)
Ad	–	v”	–	–	–
Leg II
La	–	d , bv”	(l) , σ	l’ , v’ , φ	(ft) , (tc) , (p) , (u) , (a) , s , (pv) , ω 1
Pn	–	–	–	–	–
Dn	–	(l)	–	l”	ω2
Tn	v’	–	v’	v”	(it)
Ad	–	v”	–	–	–
Leg III
La	–	d , ev’	l’ , σ	v’ , φ	(ft) , (tc) , (p) , (u) , (a) , s , (pv)
Pn	–	–	–	–	–
Dn	v’ (rarely also l’ )	l’	–	l’	–
Tn	l’	–	–	v”	(it)
Ad	–	–	–	–	–
Leg IV
Pn	–	–	–	–	ft” , (p) , (u) , (pv)
Dn	–	d , ev’	d , l’	v’ , φ	ft’ , (tc) , (a) , s
Tn	v’	–	–	l’ , v”	–
Ad	–	–	–	–	–

Note: Roman letters refer to normal setae, Greek letters refer to solenidia (except ɛ — famulus). Single quotation mark ( ’ ) designates setae on the anterior and double quotation mark ( ” ) setae on the posterior side of a given leg segment. Parentheses refer to a pair of setae. Setae are listed only for the stage in which they first appear. TABLE 2. Body setae lengths of Melanozetes paramollicomus sp. nov. during ontogeny

Body setae	La	Pn Dn Tn
Rostral	49–53	53–57 65–73 98–106
Lamellar	57–61	65–69 82–86 114–127
Interlamellar	94–102	110–123 155–180 188–205
Bothridial	53–57	57–65 61–69 69–73
Exobothridial	20–28	28–32 41–45 49–65
Epimeral	1b , 3b : 16–20; others: 1b : 20–28; others: 14– 1b : 32–36; others: 20– 1b : 41–45; 1c , 3c , 4c :
12–16	16 22 28–36; others: 24–28
Gastronotic	c 1, dm : 57–65; c 2, c 3, dp : 65–73; da , la , lm , lp , h 1:	c 1, da , la , dm : 53–65; c 2, c 2, c 3, dp , h 1: 98–106; c 3: 139–147; lm , lp : c 3, dp : 65–73; lp : 57–65; dm : 90–98; others: 73– 118–127; dp : 131–139;
41–45; h 2: 32–36; h 3: 16–20	h 1– h 3: 61–65; p 1: 32–36; 82 others: 102–110 p 2: 28–32; p 3: 24–26
Genital	–	12–16 20–22 24–28
Aggenital	–	– 20–22 24–28
Anal	–	– – 24–28
Adanal	–	– 28–32 36–41

FIGURE 6. Melanozetes paramollicomus sp. nov. , larva: A—dorsal view; B—ventral view (legs not shown); C—lateral view (gnathosoma and legs not shown). Scale bar 50 μm. Type deposition. The holotype and two paratypes are deposited in the collection of the SMNH; two paratypes are deposited in the collection of the NMB; 27 paratypes and all juvenile instars are deposited in the collection of the TSUMZ. All specimens are preserved in 70% solution of ethanol with a drop of glycerol. Etymology. The species name refers to the similarity between the new species and Melanozetes mollicomus (Koch, 1839) . Differential diagnosis. Adult of Melanozetes paramollicomus sp. nov. is similar to Melanozetes mollicomus (Koch, 1839) from the Palaearctic region (e.g. see also Shaldybina 1967 ; Seniczak 1989 a ; Pavlitshenko, 1994 ; Weigmann 2006 ) in having long, rod-like notogastral setae, but differs from the latter by the much larger body length (830–913 versus 430–590), short lamellar cusp (versus comparatively longer), long adanal setae ad 1 , ad 2 (versus comparatively shorter), thick lateral antiaxial seta on all leg tibiae I-IV and genua I-IV (versus thick lateral setae absent), and the absence of broadly dilated ventral keel of femora I, II (versus ventral keel broadly dilated). Juvenile instars of Melanozetes paramollicomus sp. nov. differs from those of M. mollicomus by the presence of comparatively very long interlamellar seta and long gastronotic setae on the gastronotic shield (versus interlamellar sea of medium length; all gastronotic setae short in larva, short or medium length in nymphs), the clavate bothridial setae, which is distally rounded (versus distally narrowed bothridial seta in M. mollicomus ), and much larger body size of the respective instars. FIGURE 7. Melanozetes paramollicomus sp. nov. , deutonymph: A—dorsal view; B—ventral view (legs except trochanters not shown); C—lateral view (gnathosoma and legs not shown). Scale bar 50 μm. FIGURE 8. Melanozetes paramollicomus sp. nov. , proto- (B, D), deuto- (A) and tritonymph (C, E): A—subcapitulum, ventral view; B, C—epimeral regions; D, E—anogenital regions. Scale bars 20 μm (A), 50 μm (B–E). FIGURE 9. Melanozetes paramollicomus sp. nov. , deutonymph:A—leg I, right, antiaxial view; B—leg II, without tarsus, right, antiaxial view; C—leg III, without tarsus, left, antiaxial view; D—leg IV, left, antiaxial view. Scale bar 20 μm. It is noteworthy that Mahunka (1984 b ) proposed Ghilarovizetes africanus Mahunka, 1984 from Tanzania , which is very similar to the present new species. The main differentiation (additionally to longer notogastral setae and presence of translamella in the new species) between these species is the number of notogastral setae, which is 15 pairs in G. africanus , while 14 pairs in M. paramollicomus sp. nov. (lacking c 1 ). Seniczak et al. (1990 , 2015 ) studied the systematic value of the notogastral setae losses in adults of Sphaerozetinae , and they emphasized the number of notogastral setae in adults has important diagnostic character, and losses of some notogastral setae, especially c 1 and c 3 have great systematic value, which is helpful for explaining the phylogeny of Ceratozetidae .According to these authors, losses of notogastral setae in adults of Sphaerozetinae is associated with the size of humeral macrosclerites in juveniles, especially in nymphs. They stated that the juveniles of Ghilarovizetes have very large humeral macrosclerite bearing all setae of c -series, while in those of Melanozetes , humeral macrosclerite is smaller, which bears only seta c 1 . These authors considered Ghilarovizetes as a most primitive genus, while Melanozetes as a derived group. In the annually updated checklist of the world oribatid mites, Subías (2004 , 2021 ) transferred both G. africanus and G. longisetosus to Melanozetes , however, as stated above, we consider these as members of Ghilarovizetes . Ontogenetic transformations Juveniles unpigmented, pale yellowish to light brown, stouter than adult. Cuticle densely and partially microsculpturing and microporose; basal part of prodorsum and anterior part of gastronotum densely tuberculate; gastronotic shield (pygidial sclerite) and partially anogenital region sparsely foveolate; anogenital region and lateral side of body with some folds. Prodorsum stockier in larva than in nymphs and adult; five pairs of prodorsal setae (including bothridial seta) constant during ontogeny; all these setae slightly longer in each stage, except bothridial seta, which has nearly same size in tritonymph and adult. The bothridial seta with short stalk and clavate head, slightly slenderer in adult than in juveniles. Juveniles have a transverse ridge between insertions of interlamellar setae, whereas the adult bears well-developed lamella. Larva bears 12 pairs of gastronotic setae, whereas in protonymph the setae of p -series are newly appeared, in adult the seta c 1 is lost. Hence protonymph bears 15 pairs of gastronotic setae, remaining unchanged in the successive stages, deutonymph and tritonymph, while the adult has 14 pairs of notogastral setae. Gastronotal setae c 2 , c 3 , dp and h 1 of deutonymph, c 3 and dp of tritonymph are relatively longer than other setae, but notogastral setae in adult mostly equal in length, except slightly longer c 3 . In juvenile instars, cupules (lyrifissures) ia , im, ih , ip , ips and iad take generally similar position, while cupule ian was not evident in both juveniles and adult. The larva has only six pairs of epimeral setae ( 1a , 1b , 1c , 2a , 3a , and 3b ), and in protonymph, seta 4a appears, seta 4b added in deutonymph, setae 3 c and 4c formed in tritonymph. Number of anogenital setae gradually increases from protonymph to adult; a pair of genital setae are formed first in protonymph, and three pairs of genital, one pair of aggenital and three pairs of adanal setae appear in deutonymph; tritonymph with five pairs of genital setae along with formation of two pairs of anal setae. Except for genital setae (six pairs in adult), the anogenital setation of tritonymph remains the same in adult instar. Paraproctal valves of larva (segment PS) with two pairs of setae, whereas those of protonymph (segment AD) and deutonymph (segment AN) are bare, but those of tritonymph have two pairs of setae. Formula of segments of paraproctal origin: 2-3-3-3-3 (PS); 0-3-3-3 (AD); 0-2-2 (AN). Leg setation increases from instar to instar as shown in Table 1 .