Humerobates aokii, Bayartogtokh & Bae, 2024

Bayartogtokh, Badamdorj & Bae, Yang-Seop, 2024, New findings of poronotic oribatid mites (Acari: Oribatida) from Korea, Zootaxa 5405 (2), pp. 151-184 : 152-158

Humerobates aokii sp. nov.

( Figures 1–4 )

Diagnosis. Body length 357–382 μm, width 252–273 μm. Rostrum rounded dorsally, with pair of lateral incisions and teeth. Prolamellar ridge absent.All prodorsal setae long, barbed. Bothridial seta composed of short, thin peduncle and large clavate, spiculate head. Lamella narrow, with large lateral tooth-like cusp. Tutorium large, distally not dentate. Notogaster with movable pteromorph, hinge well developed; ten pairs of vestigial notogastral setae; four pairs of porose areas small, circular or subcircular, with indistinct rims. Genital and aggenital setae well developed, six pairs of genital setae; anal and adanal setae represented by their alveoli. Epimeral setae short to medium long, setal formula: 3–1–3–3. Legs heterotridactylous.

Measurements. Body length 357–382 (371) μm, width 252–273 (264) μm, length of notogaster 298–319 (311) μm.

Integument. Body colour yellowish brown; microtuberculate over whole body and leg segments; excrescences of cerotegument granular; restricted to region between pteromorph, pedotectum I, tutorium and lateral side of body.

Prodorsum ( Figs. 1A, C , 2A , 4A, D ). Rostrum rounded dorsally, but slightly projecting in lateral view; with pair of lateral incisions and teeth; prolamellar ridge absent. Rostral seta (ro) arising slightly mediad of distal margin of tutorium, distinctly barbed, ~63 μm long, extending beyond tip of rostrum, curved anteromediad. Lamella narrow, ~50 μm long, with distinct cusp like large lateral tooth; translamella absent. Lamellar seta (le) ~109 μm long, barbed, inserted on medial end of lamella, extending beyond tip of rostrum. Interlamellar seta (in) ~76 μm long, barbed. Distance between bases of setae le and in about 55 and 46 μm, respectively. Exobothridial seta (ex) ~29 μm long, barbed. Bothridial seta (bs) ~42 μm long, with short peduncle barely extending from bothridium and large, clavate head, with spiculate surface. Bothridium oval, with ventrolateral and ventromedial scales; mostly covered by anterior margin of notogaster. Tutorium large, ~109 μm long, narrowed basally, with longitudinal striations, distally with prominent cusp, not dentate. Humerosejugal porose area Aj oval, ~21 μm long, hardly visible; porose areas Am, Ah not evident. Genal tooth narrow, pointed distally. Pedotectum I large, with convex dorsal margin, partly covering base of seta ex.

Notogaster ( Figs. 1A , 2A , 4A, C ). Longer than wide, ratio about 1.2:1.0; anterior margin broadly rounded. Pteromorph large, curved ventrad, with line of desclerotization. Ten pairs of notogastral setae represented by their alveoli. Four pairs of porose areas circular or subcircular, with indistinct rims, subequal in size, 16–22 μm in diameter. Opisthonotal gland opening (gla) situated lateral or anterolateral to A 1. Lyrifissures ia, im, ih, ips and ip well developed, in normal positions. Posterior notogastral tectum present.

Gnathosoma ( Figs. 1B , 4B ). Typical for family (e.g., Behan-Pelletier & Mahunka 1993; Ermilov et al. 2011). Subcapitulum wider than long; subcapitular setae a, m and h setiform, smooth, 17–21 μm long. Palp and chelicera typical for family; palpal setation: 0–2–1–3–9(+ω), solenidion bacilliform; cheliceral setae setiform, barbed; cha longer than chb.

Epimeral region ( Figs. 1B , 4B ). Epimeres without muscle sigillae; apodemes apo.2, apo.sj and apo.3 well developed. Epimeral setae smooth, 17–29 μm long, setal formula: 3–1–3–3; seta lb, 3b, 3c and 4b distinctly longer than other setae. Discidium large, projected distally; custodium short, extending anteriad to level of posterior margin of leg acetabulum II. Circumpedal carina short, not reaching to base of pedotectum I, but complete laterally, reaching margin of ventral plate.

Anogenital region ( Figs. 1B , 4B ). Genital and aggenital setae well developed; six pairs of genital setae, g 1 – g 4 inserted along anterior margin of genital plate, g 5 and g 6 close to posterior margin. Anal and adanal setae represented by their alveoli; ad 1 and ad 2 inserted posterior, ad 3 lateral to anal aperture. Lyrifissure iad located close and parallel to anterolateral margin of anal aperture. Postanal porose area small, oval.

Legs ( Figs. 2B , 3 ). Medial claw thicker than lateral claws, tarsi without pulvillus. Ventral spur on genua II, III and femur II strongly developed. Porose area present proximoventrally on tarsi I–IV; porose areas on femora I–IV and trochanters III and IV large. Lateral antiaxial seta l ” on tibia I and genua I, II thick; seta s of tarsus II similarly barbed to other setae on this segment. Formulas of leg setae: I (1–5–3–4–20), II (1–5–3–4–15), III (2–3–1–3–15), IV (1–2–2–3–12); formulas of solenidia: I (1–2–2), II (1–1–2), III (1–1–0), IV (0–1–0); homology of setae and solenidia indicated in Table 1 .

Material examined. Holotype (female) and three paratypes (one male and two females): San 171, Taeha-ri , Seo-myeon , Ulleung-gun , North Gyeongsang Province, Korea, 37°29’35.13”N, 130°49’40.71”E, soil and litter of mixed forest composed by Siebold humlock ( Tsuga sieboldii Carrière ), Japanese white pine ( Pinus parviflora Siebold and Zuccarini ) and Engler’s beech ( Fagus engleriana Seemen ex Diels ), 26 May 2022, Coll. T. G. Lee.

Etymology. This species is named in memory of the eminent acarologist and soil zoologist, Dr. Jun-ichi Aoki, Professor emeritus of the Yokohama National University, Japan, who has introduced generations of students to the discipline of acarology and soil zoology during his exemplary career as researcher and teacher. His enormous scientific career and influential works have always inspired the generations of soil acarologists, and influenced the creations of many young researchers.

Remarks. At a glance of superficial view, both new species proposed here remind us of Chamobates species. The presence of the large lateral tooth distally on lamellae, insertion of the lamellar setae on the surface of prodorsum, absence of the prolamellar ridge, lamellar cusps and translamella all contribute to this appearance. However, both new species have hinged pteromorphs, i.e., with clearly developed line of desclerotization, which is the principal character state that can distinguish the families Chamobatidae and Humerobatidae .

It should be noted that most species of Humerobates have a pair of prolamella-like longitudinal ridge on their rostral region (e.g., see Hammer 1967; Pérez-Iñigo & Pérez-Iñigo 1993; Choi 2004; Weigmann 2006), which is absent in both of our new species. Also, most species of Humerobates have short, but distinctly developed lamellar cusps and incomplete transamella, and the lamellar setae are inserted on the lamellar cusps. However, in both of our newly proposed species, lamellar cusps are not developed, but the lamellae have large lateral tooth distally, and the lamellar setae are inserted on the surface of the prodorsum.

The present new species clearly differs from all other known species of Humerobates in the relatively small circular or subcircular porose areas with indistinct rims; development of large cusp-like lateral tooth of lamellar cusp; ventrally bent pteromorph with no radiating vein-like ridges, and absence of anal and adanal setae, which represented by their alveoli.

Two species previously recorded in Korea, Humerobates flechtmanni Pérez-Iñigo & Pérez-Iñigo, 1993 and Humerobates nudus ( Hammer, 1967) are distinguishable from the present new species in the oval and much larger notogastral porose areas, especially Aa (vs. small, round porose areas in the new species); much longer interlamellar setae, which extending beyond rostrum (vs. relatively short setae in not reaching rostrum in the new species); large pteromorphs extended laterally with many radiating vein-like ridges (vs. pteromorphs small, bent down, without vein-like ridges in the new species); lamellar cusps with no lateral tooth (vs. lamellar cusps with large cusp like lateral tooth in the new species); and well-developed anal and adanal setae (anal and adanal setae represented by their alveoli in the new species).

Figures

FIGURE 1. Line drawing images of Humerobates aokii sp. nov. A—Dorsal view; B—Ventral view of body; C—Prodorsum.

FIGURE 2. Line drawing images of Humerobates aokii sp. nov. A—Lateral view of body; B—Leg I, right, antiaxial view.

FIGURE 3. Line drawing images of Humerobates aokii sp. nov. A—Leg II, right, antiaxial view; B—Leg III, right, antiaxial view; C—Leg IV, right, antiaxial view.

FIGURE 4. Compound microscopic images of Humerobates aokii sp. nov. A—Dorsal view; B—Ventral view of body; C—Lateral view of hysterosoma, D—Lateral view of proterosoma.

Tables

TABLE 1. Leg setation and solenidia of adult Humerobates aokii sp. nov.

Leg	Tr	Fe	Ge	Ti	Ta
I	v’	d, (l), bv”, v”	(l), v’, σ	(l), (v), φ, φ 1 2	(ft), (tc), (it), (p), (u), (a), s, (pv), v’, (pl), l”, ɛ, ω, ω 1 2
II	v’	d, (l), bv”, v”	(l), v’, σ	(l), (v), φ	(ft), (tc), (it), (p), (u), (a), s, (pv), ω, ω 1 2
III	l’, v’	d, l’, ev’	l’, σ	l’, (v), φ	(ft), (tc), (it), (p), (u), (a), s, (pv)
IV	v’	d, ev’	d, l’	l’, (v), φ	ft”, (tc), (p), (u), (a), s, (pv)

Note: Roman letters refer to normal setae, Greek letters 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.