Tuckerella fossilibus Khaustov, Sergeyenko & Perkovsky, 2014

Sidorchuk, Ekaterina A. & Khaustov, Alexander A., 2018, Two Eocene species of peacock mites (Acari: Tetranychoidea: Tuckerellidae), Acarologia 58 (1), pp. 99-115 : 106-110

Tuckerella fossilibus Khaustov, Sergeyenko & Perkovsky, 2014 .

( Figs 5–7 )

Tuckerella fossilibus Khaustov, Sergeyenko & Perkovsky, 2014, p. 367 , Figures 1–5 .

Redescription — Deutonymph. Length of idiosoma – 245, width – 165.

Gnathosoma ( Figs 5D , 7B, C ) — Left palp covers main part of right palp dorsally, both palps preserved in a way to cover infracapitulum dorsally. Palpgenu dorsally with seta d slightly not reaching base of tibial claw. Palptibia with large, hooked tibial claw and three pairs of setae: d slightly longer than length of palpgenu; short l”, reaching to tip of tibial claw; medium-sized l’, about length of palptibia+tibial claw. Inner margin of tibial claw transversely striate. Palptarsus with 5 visible phaneres: 3 terminal, blunt-ended (probably palpal eupathidia), one short dorsal and one short ventral. Subcapitulum long and narrow with visible stylet protruding apically ( Figs 5D , 7B , st); ventrally with one pair of long subcapitular setae m. Peritremes not evident. Oval stylophore, ca 100x40, visible inside body ( Figs 5A , 6 , sty).

Idiosomal dorsum ( Figs 5 , 6 , 7B ) — Cuticular ornamentation, where visible anterodorsally, irregularly reticulate ( Fig. 5A ). Number of dorsal idiosomal setae as in T. weiterschani n. sp. Setae v 2, sc 1 and sc 2 fan-like ( Fig. 5C, D ); v 1 considerably different from other prodorsal setae, with smooth margins and weakly tapered tip ( Figs. 5D , 7 ). Two pairs of eyes located anterolaterally to bases of setae sc 1; posterior eye distinctly larger than anterior ( Fig. 7B , oc). All setae of C, D, E and F-rows broad, flat, ovate to obovate in shape: c 1 - c 3, d 1 - d 3 and e 1, e 2 of medium size, subequal (16 – 18 x 24 – 28); f 1 and f 2 slightly smaller than e 1 and e 2; f 2 situated on same transverse level as f 1. Lateral setae c 5 - c 7, d 4 - d6 and e3 distinctly larger than central, more elongate, with rounded tips, largest d 6 28 x 60. Setae h 1 large, flat, obovate (27 x 55), setae h 2 – h 8 flagellate: h 2, h 4, h 5, h 7 long, barbed, tapered (180, 270, 180, 220 respectively), h 6 short, thick, heavily barbed, blunt (40); h 3, h 8 intermediate in length and thickness, barbed, tapered (80). Only anterior margins of dorsal shields C and D clearly visible ( Fig. 6 ).

Idiosomal venter ( Figs 5B , 7A, D, E, F ) — Dark and collapsed, obscured by legs. Only coxal setae are partly discernible: 1a-c and 2b smooth, fine, 1a longest; 2c long, thick, heavily barbed. Genital and anal openings indiscernible.

Legs ( Fig. 7 ) — Dark and curled, mostly visible in ventral aspect, with some setae poorly discernible. Leg I ( Fig. 7A, B ): trochanter without visible setae; femur with three large obovate setae (d, l’, l”) and setiform bv”, other ventral setae not visible. Genu with three large obovate setae (d, l’, l”) and setiform v”, other ventral setae not visible. Tibia with large, obovate seta l” and narrower d, l’; ventral setae not visible; solenidion φ baculiform, situated on short tubercle. Tarsus with two claws and empodium, each with clearly visible tenent hairs; two solenidia present, ω 1 about 2 times longer than ω 2; setae: (u) simple and short, abaxial ” () members of pairs (ft) and (pl) long, distinctly longer than tarsus, pl’ about half shorter on right leg, absent on left leg; (tc) situated on tubercles, fine, tapered, (p) blunt, short, apparently eupathidial, difficult to discern where hidden behind ambulacrum; pv’ setiform. Leg II ( Fig. 7C, D ): trochanter not discernible; femur with long, thick, heavily barbed seta bv” and 3 obovate large setae d and (l) (d and l” artificially split on left leg); genu with 3 obovate setae visible; tibia with 3 obovate and one or two long simple seta visible (( v) on left, only v” on right leg); tarsus with ambulacrum as in leg I (well visible on right leg), one solenidion, and 10 smooth setae: long ft”, shorter ft’, (pl), (tc), (u) (one member of pair visible on each leg), p” and pv’. Leg III ( Fig. 7E, F ): trochanter with single visible seta l’ thick, long, heavily barbed; femur with small obovate seta d and smooth simple ev ’; genu with single visible small obovate seta l’; tibia with 2 clearly visible setae, simple v ’ and small obovate l’ (visible transversally on right leg), and one spot that may be alveolus of seta d; tarsus with ambulacrum like in leg II and 7 simple setae (only 4 clearly visible on right leg): (ft), (tc), (u) and pv’. Leg IV ( Fig. 7 H, J ): poorly visible, dark, trochanter and setation of femur indiscernible; genu with one well visible narrowly obovate seta d on left leg, no visible setae on right; tibia with 2 ventral setae well visible, two discernible on right leg, one well visible seta and one discernible on left; tarsus with two claws discernible, 3 setae visible on left and one on right leg. See figure for possible setal homologies. Observed setation (trochanter to tarsus, solenidia in parentheses): leg I:?-5-3-4(1)-11(2); leg II:?-4-3-5-10(1); leg III: 1-2-1-2/3?-7; leg IV:?-?-1-2?/4?-?.

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Remarks — Khaustov et al. (2014) in original description of T. fossilibus were not able to identify its life stage. Now, after more detailed description we can suggest that it is probably a deutonymph. Our opinion is based on the setation of leg I, which shows: (1) two tarsal solenidia, (2) absence of the tarsal seta l 1 ’, (3) three obovate setae on each genu and tibia. According to observations by Quiros-Gonzalez and Baker (1984), Lindquist (1985), Beard and Walter (2005) and Beard et al. 2013, although there is some interspecific variation, the second tarsal solenidion is deutonymphal, tarsal seta l 1 ’ is tritonymphal, and three obovate setae on first genu and tibia are only present in deutonymphs: known protonymphs are found to have 1–2 obovate setae per segment, while tritonymphs and adults have five.

Addition to the differential diagnosis — Certain caution is necessary when using this comparison, for the immature specimen is being compared to adults. Based on the available descriptions ( Quiros-Gonzalez and Baker 1984, Lindquist 1985, Beard and Walter 2005, Beard et al. 2013), ontogenetic changes of the opisthonotal setation may affect setae v 1 (in T. revelata they are obovate, with rough edge, in larva, with outline smoothing out in the subsequent stages), leaf-shaped C-H-row setae (relatively narrower and more tapered in the immatures) and flagellate H-row setae (becoming relatively shorter during ontogeny). T. fossilibus is so far unique tuckerellid species known to have obovate setae h 1 similar in size to the lateral setae of C-, D- and E rows. By the shape of proterosomal setae v 1 and the relative shortness of setae h 1 and h 6, deutonymphal T. fossilibus is similar to adults of T. pavoniformis ( Ewing, 1922) , T. indica Prasad, 1973 and T. channabasavannai Malik and Kumar, 1992 . It differs from them by much larger setae h 1 and by the differentiated shapes of the other H-row setae T. ( pavoniformis has setae h 2 - h 5, h 7 and h 8 all similar, whip-like ( Baker and Pritchard 1953), as do T. indica and T. channabasavannai ). By the shape of setae v 1 T. fossilibus is also similar to T. japonica Ehara, 1975 and to T. kumaonensis Gupta, 1979 , but these species have three pairs of comparatively small leaf-like setae in h -series.

Holotype container — Amber fragment with holotype, sized 2x1x 0.5 mm, is mounted in the Buehler EpoThin epoxy resin between two 1 cm coverslips. The preparation is glued with a low-temperature hot-melt adhesive to a 1.5 mm-thick transparent plastic frame ( Fig. 5A ).

Figures

Figure 1 Tuckerella weiterschani n. sp. holotype. Layered DIC micrographs: A – dorsal view, inserts show two aspects of amber piece containing holotype and its package, not to scale; B – ventral; C – posterior; D, E, details of idiosomal setae, ventral view; F, eyes; G, posterior idiosomal setae laterally; H, detail of prodorsal setav1 and peritreme; J, lateral aspect. Rectangles in A, B, J show positions of Figs D-G. Abbreviations: an, anal area; ge, genital area; oc, eyes, per, peritreme; plp, palp; sub, subcapitulum; I–IV, legs.

Figure 2 Tuckerella weiterschani n. sp. holotype. Layered POL micrograph. Gnathosoma laterally, arrow points to adoral seta. Abbreviations: palp segments: Fe, femur; Ge, genu; Ta, tarsus; Ti, tibia; ti.cl, palptibial claw.

Figure 3 Tuckerella weiterschani n. sp. holotype dorsally.

Figure 4 Tuckerella weiterschani n. sp. holotype details. A’, right tarsus I adaxially; A, left leg I abaxially, gnathosoma and anterior idiosoma dorsally; B, leg II abaxially; C, leg III abaxially; D, leg IV abaxially; D’, tarsus and tibia IV dorsally. Abbreviations: oc, eyes; per, peritreme; plp, left (poorly visible) palp; sub, subcapitulum; ti.cl, palptibial claw. Gray lines represent poorly discernible structures.

Figure 5 Tuckerella fossilibus Khaustov, Sergeyenko & Perkovsky, 2014 holotype deutonymph. Layered DIC micrographs: A – dorsal view, rectangles show positions of figures C, D, insert shows container with holotype; B – ventral; C – detail of idiosomal setae; D – left leg I and anterior proterosoma dorsally. Abbreviations: st, cheliceral stylets; sty, stylophore; ta, palptarsus; ti.cl, palptibial claw.

Figure 6 Tuckerella fossilibus Khaustov, Sergeyenko & Perkovsky, 2014 holotype deutonymph dorsally. Abbreviation: sty, stylophore.

Figure 7 Tuckerella fossilibus Khaustov, Sergeyenko & Perkovsky, 2014 holotype deutonymph detail: A – right tarsus I in ventral view of mite; B – leg I, gnathosoma and anterior proterosoma, dorsal view; C–J, legs in ventral view of mite: C – right leg II; D – left leg II and seta 3a; E – right leg III F – left leg III; H – right leg IV; J – left leg IV. Abbreviations: oc, eyes; st, cheliceral stylets; ta, palptarsus; ti.cl, palptibial claw. Gray lines represent poorly discernible structures.