Melanozetes avachai, Seniczak & Kaczmarek & Seniczak, 2016

Seniczak, S., Kaczmarek, S. & Seniczak, A., 2016, Morphological ontogeny of Melanozetes avachai n. sp., a unique member of Melanozetes (Acari: Oribatida: Ceratozetidae), Acarologia 56 (4), pp. 463-484 : 464-478

Melanozetes avachai n. sp.

Diagnosis — Adult relatively long (length of females 831 – 864, and males 717 – 799), with characters of Melanozetes ( Shaldybina 1975) . Lamellar cusp short, translamella usually absent, but may be present or incomplete. Seta le almost as long as in, sensillus clavate. Notogastral setae with barbs. Femora I and II oval in cross section, without ventral carina. Larva without gastronotal shield and seta c 1 inserted on microsclerite, not on humeral macrosclerite, nymphs with uniform gastronotal shield bearing 10 pairs of smooth setae, c 1 on humeral macrosclerite, c 2, c 3, p 2 and p 3 on microsclerites. Humeral organ present. Femora I and II oval in cross section, without ventral carina.

Description of adult — Body oval in dorsal aspect ( Figure 1 ), females usually slightly larger than males. Measurements: length of holotype (female 799), mean of 30 females - 810.1 (range 831 – 864) and 30 males - 751.4 (range 717 – 799); notogaster width of holotype (455), mean of 30 females - 491.4 µm (range 462 – 546) and 30 males - 443.9 µm (range 423 – 468).

Integument — Posterior part of prodorsum, central part of notogaster and ventral plate microporose, with light dots ( Figure 1B ), marginal parts of notogaster and pteromorphs microporose and reticulate ( Figure 1C ), other parts of body microporose.

specimens in µm).

Prodorsum — Subtriangular, rostrum rounded ( Figure 1 ). Seta ro relatively long ( Table 1), positioned laterally and barbed laterally. Seta le nearly as long as in, barbed, acuminate, seta ex short. Lamella (La) long (118 – 122), with longitudinal striae, translamella (tr) usually absent, but may be present or incomplete ( Figure 2 ), lamellar cusp short (10) and rounded. Bothridium (bo) with welldeveloped medial and lateral scales; sensillus (ss) short ( Table 1), clavate, with smooth stalk and barbed head. Humerosejugal porose area Aj oval.

Notogaster — Longer (females 585 – 650, males 520 – 585) than wide (females 462 – 546, males 423 – 468), with well-developed, immovable pteromorphs. Notogastral setae (14 pairs, including c 2 and c 3) relatively long ( Figures 1 , 3A ; Table 1) and barbed. Lyrifissures ia, im, ip, ih, ips and opisthonotal gland opening (gla) and porose areas (4 pairs) in normal position, Aa largest.

Gnathosoma — Subcapitular seta h longer (45) than m (41) and a (31); all smooth ( Figure 4 ). Chelicera (length 209 – 212) with seta cha (64) barbed and chb (33) smooth ( Figure 5D ). Axillary saccula of subcapitulum (sac) short (16). Palp (length 126 – 129) with seta inf barbed, other setae smooth ( Figures 5 A-C). Formula of palp setae (trochanter to tarsus + solenidion ω): 0-2-1-3-9(1).

Epimeral and lateral regions — Central epimeral setae (1a, 2, 3a, 3b, 4a, 4b) short (18 – 22) and smooth ( Figure 4 ), marginal setae longer (37 – 41), and finely barbed, 1b longest (51). Tutorium (tu) long (148 – 162) and narrow, and distally pointed. Humerosejugal porose areas Am and Ah and sublamellar porose are Al present. Pedotectum I (pd1) large, oval (131 × 56), with longitudinal striae ( Figure 3A ). Genal tooth (gt) long (38), narrow and pointed, custodium (cus) shorter (20), triangular and blunt. Discidium (dis) triangular. Circumpedal carina (cp) wellformed.

Anogenital region — Genital setae (six pairs) about equally as long (15 – 18) as aggenital (one pair), adanal (three pairs) and anal (two pairs) setae ( Figure 4 ). Lyrifissures iad short, located close to anterior end of anal opening. Postanal porose present.

Legs — Femora I and II oval in cross section, without ventral carina. Porose areas present on paraxial side of femora I-IV and trochanters III and IV. Solenidion ω 2 on tarsus I longer than ω 1, and located anterolateral to ω 1; famulus short, seta ft" minute ( Figure 6 ); solenidia ω 1 and ω 2 on tarsus II of similar size. Seta l" on genua I and II and seta d on femora III and IV thicker than other leg setae. Formulae of leg setae [trochanter to tarsus (+ solenidia)]: I - 1-5-3(1)-4(2)-20(2); II - 1-5-3(1)-4(1)-15(2); III - 2-3-1(1)-3(1)-15; IV - 1-2-2-3(1)-12 ( Table 2).

Description of juveniles — Larva oval in dorsal view ( Figure 7 ), main body unpigmented, except light brown sclerites and legs. Prodorsum triangular, with setae ro and le of medium size, in long ( Table 1) and ex short; all barbed. Mutual distance of setae ro> mutual distance le> greater than mutual distance in; pair le inserted approximately in midway between pairs ro and in. Opening of bothridium rounded, sensillus clavate with barbed head. Lateral depression present above leg I. Prodorsum porose, porosity denser posteriorly.

Gastronotum of larva ( Figures 7 , 8A ) unsclerotized, except for three pairs of glabrous, aligned macrosclerites (well-formed humeral macrosclerite and two elongated lateral macrosclerites), and 12 pairs of setae, including h 3 inserted lateral to middle part of anal valves. Gastronotal setae (12 pairs) short and barbed, except smooth h 2 and minute h 3, inserted lateral to middle of anal valves; all on microsclerites, except h 3; other microsclerites present in central part of gastronotum. Cupule ia posteroventral to seta c 3, cupule im posterior to seta lm, cupule ip lateral to seta h 2, cupule ih lateral to anterior end of anal opening; opisthonotal gland opening gla on microsclerite, lateral to ih and humeral organ (oh) located anterolateral to seta c 3. Paraproctal valves (segment PS) glabrous.

Main body of protonymph and legs light brown. Compared to larva, prodorsum relatively shorter, setae slightly longer ( Table 1), and sensillus relatively slimmer. Gastronotum with 15 pairs of setae due to appearance of p -series ( Figure 9A ), which are retained by subsequent nymphs ( Figures 10A, B ); all setae smooth, except barbed c 1 and c 2. Seta c 1 inserted on humeral macrosclerite, c 2 and c 3 on microsclerites. Gastronotal macrosclerite uniform, reticulate, with 10 pairs of setae (d -, l -, h -series and p 1); setae p 2 and p 3 on microsclerites. In protonymph one pair of genital setae on genital valves, and two pairs are added in both deutonymph and tritonymph. Opisthonotal gland opening gla lateral to seta lp, with dark, porose sclerite, humeral organ oh located anterolateral to seta c 3. Deutonymph with one pair of aggenital setae and three pairs of adanal setae ( Figure 10A ), remaining in subsequent instars; all short and smooth. Tritonymph with two pairs anal setae on anal valves ( Figure 10B ). Prodorsum of tritonymph relatively shorter ( Figure 10 ; Table 1) than in other nymphs, but setae similar. Lateral integument with five macrosclerites, four elongated and one smaller ( Figure 8B ). Cupules ia and im placed as in larva, cupule ip between setae p 1 and p 2, cupule iad lateral to anterior part of anal valves, cupules ips and ih displaced posterolateral to iad. Setae of p -series (three pairs) longer than ad -series (three pairs) and an -series (two pairs); all smooth, p 2 and p 3 on microsclerites ( Figure 10B ). Genital setae (five pairs) and aggenital setae (one pair) short and smooth. Femora I and II oval in cross section, without ventral carina. Location and shape of solenidia on tarsus I of tritonymph ( Figure 11 ) similar as in adult, but some setae on leg segments (d on femora I and II and genu IV, l" on genua I and II and tibia II, l’ on genu and tibia III and tibia IV, v’ on tibia III and IV) thicker.

Summary of ontogenetic transformations — Setae ro and le are of medium size, in is long and ex is short in all juveniles, whereas in the adult ro and le are long, but ex remains short. The sensillus is relatively thicker in the larva than in the nymphs and adult. The larva has 12 pairs of gastronotal setae, including h 3, the nymphs have 15 pairs. A humeral macrosclerite is present in all juvenile instars, but in the larva it is glabrous and in the nymphs it bears seta c 1. Gastronotal macrosclerite is absent in the larva and is well-formed in the nymphs. The notogaster of adult loses seta c 1. The number of leg setae and solenidia increases during the ontogeny ( Table 2), but some setae of tritonymph are thicker than in the adult.

Ecology and biology — We found M. avachai n. sp. in one sample (1 dm 3) in dense moss in the floor of deciduous forest, with alder dominating and some birch. Density of oribatid mites was 345 individuals per 500 cm 3, with M. avachai the dominant oribatid mite (59.8 %). In M. avachai , the adults dominated (67 % of all individuals), and the stage structure of this species was the following: 22 larvae, 38 protonymphs, 3 deutonymphs, 6 tritonymphs and 137 adults. The mean sex ratio (females to males) was 1:1.5. Most females (87 %) were gravid and carried 4-5 large eggs.

Type deposition — The holotype and 6 paratypes (in 70 % ethanol) are deposited in the University Museum of Bergen ( Norway) and 6 paratypes are deposited in the Department of Evolutionary Biology , Kazimierz Wielki University, Bydgoszcz, Poland .

Etymology — The species epithet avachai refers to the Avacha volcano (Kamchatka, Russia), the type locality.

Figures

FIGURE 1: Melanozetes avachai n. sp., adult: A – dorsal aspect, legs partially drawn, scale bar 100 µm; B – microporose notogaster, with light dots and seta da; C – reticulate pattern of pteromorph.

FIGURE 2: Melanozetes avachai n. sp., adult, prodorsum and part of notogaster, legs partially drawn, scale bar 50 µm: A, B – different individuals, showing variation in form of translamella.

FIGURE 3: Melanozetes avachai n. sp., adult, legs partially drawn, scale bars 100 µm: A – lateral aspect; B – anogenital region.

FIGURE 4: Melanozetes avachai n. sp., adult, anterior half of ventral side, legs removed, scale bar 50 µm.

FIGURE 5: Melanozetes avachai n. sp., antiaxial aspect, scale bars 20 µm: A, B, C – palps of adult, tritonymph and larva, respectively; D – chelicera of adult, a hole through the chelicera partially shows the Traghardh’s organ on the opposite side.

FIGURE 6: Melanozetes avachai n. sp., adult, leg segments, antiaxial aspect, setae on the opposite side are not illustrated (in brackets), scale bar 20 µm: A – leg I, femur (l’), genu (l’), tibia (l’), tarsus (pl’); B – region of solenidia ω1 and ω2 on tarsus I; C – leg II, femur (l’), tibia (v’); D – leg III, tibia (v"); E – leg IV.

FIGURE 7: Melanozetes avachai n. sp., larva: A – Dorsal aspect, legs partially drawn, scale bar 50 µm; B – gastronotal seta c1.

FIGURE 8: Melanozetes avachai n. sp., lateral aspect, legs partially drawn, scale bars 50 µm: A – larva; B – tritonymph.

FIGURE 9: Melanozetes avachai n. sp., lateral aspect, legs partially drawn, scale bars 50 µm: A – larva; B – tritonymph.

FIGURE 10: Melanozetes avachai n. sp., legs partially drawn, anogenital region, scale bars 50 µm: A – deutonymph; B – tritonymph.

FIGURE 11: Melanozetes avachai n. sp., tritonymph: A – Dorsal aspect, legs partially drawn, scale bar 100 µm; B – part of gastronotum with seta c2; C – part of gastronotum with seta da.