Elliptochthonius profundus Norton, 1975

Ermilov, Sergey G. & Bayartogtokh, Badamdorj, 2022, Ontogenetic instars of Elliptochthonius profundus Norton, 1975 (Acari, Oribatida, Elliptochthoniidae), with remarks on juveniles of the superfamily Parhypochthonioidea, Zootaxa 5187 (1), pp. 53-68 : 54-61

Elliptochthonius profundus Norton, 1975

( Figs 1–9 )

Diagnosis of adult ( Figs 1 , 2 ). Body elongate oval, dorsoventrally flattened, widest at level of notogastral setae d 3. Body size: 565–595 × 200–209. Body colour light yellowish. Surface sparsely microfoveolate; prodorsum tuberculate sculpturing; posterior part of gastronotum with large foveolae; lateral and ventral sides partially striate. Rostrum laterally with irregular teeth. Rostral, lamellar, anterior and posterior exobothridial setae short, simple; interlamellar seta long, slightly lanceolate; bothridial seta fusiform, shortly ciliate. Dorsal or postpedal transverse scissure developed between setal rows d and e. With 16 pairs of slightly lanceolate notogastral setae; of these, anterior notogastral half with six pairs (setal rows c, d), posterior notogastral half with 10 pairs (setal rows e, f, h, p). Four pairs of subcapitular and one pair of adoral setae simple. Palp four-segmented; setation: 1-0-2-7(+ω). Cheliceral seta cha short, needle-shaped; chb long, simple. Supracoxal seta present. Epimeres I and II separated medially by membrane, epimeres III and IV fused medially. Setal formulas for epimeres: 3-2-3-4. With eight pairs of genital (on plate six setae in paraxial row, two setae in antiaxial row), one pair of aggenital, three pairs of anal, four pairs of adanal setae. Leg tarsi tridactylous, with a highly reduced central claw. Famulus bifurcate. Number of solenidia on genu-tibia tarsus: I: 2-1-3; II: 1-1-1; III, IV: 1-1-0.

Description of juvenile instars ( Figs 3–9 ). Form. Body elongate oval, but much stout than adults (especially larva), slightly flattened dorsoventrally.

Measurements. Total length of larva: 215–232; protonymph: 282–298; deutonymph: 365–381; tritonymph: 415–431. Total width of larva: 83–99; protonymph: 99–116; deutonymph: 132; tritonymph: 149–166.

Integument ( Figs 3 – 5 ). Body cuticle colourless except posterior part of gastronotic region light brown. Surface sparsely microfoveolate; foveolae mostly very small, visible under high magnification in dissected specimens, but foveolae in posterior part of gastronotic region larger, distinctly visible. Prodorsum and lateral side of gastronotic region tuberculate; tubercles in basal part of prodorsum largest. Gastronotic region near scissure transversely striate; sternal region longitudinally striate; lateral part of gastronotic region and cuticle near aggenital and adanal regions striate.

Prodorsum ( Figs 3A, C ; 5A ). Relatively long, about 1/2 (in larva) and 1/3 (in nymphs) length of gastronotic region (measured in lateral view). Rostrum broad, laterally with slight irregular teeth. Rostral, lamellar, interlamellar, anterior exobothridial and posterior exobothridial setae setiform, slightly barbed; seta in comparatively long, much longer than other prodorsal setae. Bothridial seta fusiform, shortly ciliate. Setae lengths during ontogeny as presented in Table 1 .

Gastronotic region ( Figs 3 – 5 ). Gastronotum widest at level of setae c 3 and/or d 3, tapering posteriorly. Dorsal transverse scissure well visible, located between setal rows d and e, continuing lateroventrally. Larva with 13 pairs, nymphs with 16 pairs of gastronotic setae; of these, anterior gastronotic part (before scissure) with six pairs of setae (setal rows c, d), posterior gastronotic part (behind scissure) with seven and 10 pairs (except paraproctal setae) of setae in larva and nymphs, respectively. All setae (except thin, smooth p 1 – p 4 on paraproctal segment in larva) setiform (centrodorsal setae usually slightly blunt-ended), barbed. Strong ventral ridge developed anterior to setae h 1 in larva and protonymph, anterior to p 1 and p 2 in deuto- and tritonymphs. Opisthonotal gland opening and cupules ia, im, ip well visible. Setae lengths during ontogeny as presented in Table 1 .

Gnathosoma ( Fig 6 ). Subcapitulum slightly longer than wide, simple, without secondary articulation. All subcapitular setae setiform, slightly barbed, similar in thickness; m 2 (fourth pair of subcapitular setae) added in deutonymph. One pair of adoral setae setiform, smooth. Dorsal and lateral lips smooth. Palp four-segmented, trochanter and femur fused; setation: 1-0-2-7(+ω); solenidion of palptarsus long, free, bacilliform. Postpalpal seta thorn-like, blunt-ended, smooth. Chelicera with two setae and some chitinous barbs on both antiaxial and paraxial sides; cha needle-shaped; chb setiform, smooth. Gnathosoma and setae lengths during ontogeny as presented in Table 2 .

Epimeral and lateral podosomal regions ( Figs 3B, C ; 4B, C ; 5B ). Supracoxal seta eI thorn-like, smooth. Claparède’s organ long, clavate. Setal formulas for epimeres in larva: 3-1-2; protonymph: 3-2-3-1; deutonymph and tritonymph 3-2-3-4. Setae 1c in larva modified to ring-like thickening structure; others setiform, thin, roughened. Setae lengths during ontogeny as presented in Table 1 .

Anogenital region ( Figs 3B ; 4B, C ; 5B ). Ontogeny of genital, aggenital, adanal, and anal setal formulas, from larva to tritonymph: 0-1-3-6, 0-0-1-1, 0-4-4-4, 0-0-3-3, respectively, paraproctal segment of larva with four pairs of setae p. All setae setiform, thin, smooth or slightly roughened. In deutonymph, genital setae on genital plate inserted in one row; in tritonymph, four setae in paraxial row, two setae in antiaxial row. Aggenital seta inserted at level of g 2. Cupules ih, ips, iad, and ian appearing in normal ontogenetic pattern. Setae lengths during ontogeny as presented in Table 1 .

Legs ( Figs 7 – 9 ). Claw of each leg slightly barbed dorsally. Formulas of leg setation (including famulus) and solenidia in larva: I (0-2-3-5-17) [2-1-1], II (0-3-3-4-12) [1-1-1], III (0-2-2-3-11) [1-1-0]; protonymph: I (0-3-4-5- 18) [2-1-1], II (0-3-4-4-12) [1-1-1], III (1-2-2-3-11) [1-1-0], IV (0-0-0-0-5) [0-0-0]; deutonymph: I (0-4-5-6-19) [2-1-2], II (1-4-4-4-12) [1-1-1], III (2-2-3-3-11) [1-1-0], IV (1-2-1-2-11) [1-1-0]; tritonymph: I (0-6-5-6-19) [2-1-3], II (1-4-4-4-14) [1-1-1], III (2-2-4-3-12) [1-1-0], IV (1-2-3-4-11) [1-1-0]. Homology of leg setae and solenidia as indicated in Table 3 . Famulus bifurcate, with long setiform and short bacilliform branches. Solenidia ω 1 on tarsus I and ω on tarsus I thick, bacilliform; ω 2 and ω 3 on tarsus I setiform; φ on tibia I and σ’, σ” on genu I rod-like; φ on tibiae II – IV and σ on tibiae II – IV bacilliform.

Figures

FIGURE 1. Elliptochthonius profundus Norton, 1975, adult, SEM micrographs: A, B—dorsal view; C—ventral view; D— lateral view; E—dorsoanterior view; F – prodorsum, dorsal view.

FIGURE 2. Elliptochthonius profundus Norton, 1975, adult, SEM micrographs:A—gnathosoma, ventral view; B—gnathosoma, lateral view; C—notogastral seta f1; D—first pair of legs and anterior part of gnathosoma, ventral view.

FIGURE 3. Elliptochthonius profundus Norton, 1975, larva: A—dorsal view (legs not shown); B—ventral view (gnathosoma and legs shown partially); C—lateral view (gnathosoma and legs shown partially). Scale bar 50 μm.

FIGURE 4. Elliptochthonius profundus Norton, 1975, juvenile instars:A—larva, posterior view; B—protonymph, ventral view (gnathosoma and legs shown partially); C—deutonymph, ventral view (gnathosoma and legs shown partially). Scale bars 50 μm.

FIGURE 5. Elliptochthonius profundus Norton, 1975, tritonymph: A—dorsal view (legs not shown); B—ventral view (gnathosoma and legs shown partially). Scale bar 50 μm.

FIGURE 6. Elliptochthonius profundus Norton, 1975, larva (A, C, E) and tritonymph (B, D, F): A, B—subcapitulum, ventral view; C, D—palp, right, antiaxial view; E—chelicera, right, antiaxial view; F—chelicera, left, paraxial view. Scale bars 20 μm.

FIGURE 7. Elliptochthonius profundus Norton, 1975, larva: A—leg I, right, antiaxial view; B—leg II, right, antiaxial view; C—leg III, left, antiaxial view. Scale bar 20 μm.

FIGURE 8. Elliptochthonius profundus Norton, 1975, proto- (A, B) and deutonymphs (C): A —leg I, right, antiaxial view; B—leg IV, left, antiaxial view; C—leg IV, right, paraxial view. Scale bar 20 μm.

FIGURE 9. Elliptochthonius profundus Norton, 1975, tritonymph: 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 20 μm.