Scutoribates perornatus Sellnick, 1918

Sidorchuk, Ekaterina A. & Norton, Roy A., 2010, Redescription of the fossil oribatid mite Scutoribates perornatus, with implications for systematics of Unduloribatidae (Acari: Oribatida), Zootaxa 2666, pp. 45-67 : 48-58

Scutoribates perornatus Sellnick, 1918

( Figs. 1 –33, 38–41, 43–53, 57, 59)

Diagnosis. Scutoribates (see below) with adults having total length 492–543 μm, width 258–288. Cerotegument thick, blocky on posterior of notogaster, thin and amorphous on anterior notogaster and on venter. Lamellar cusp terminating in two points, on either side of narrowly foliate lamellar seta. Interlamellar and notogastral setae subclavate, broadest distally, barbed, inclined; former about twice length of notogastral and adanal setae. Bothridial seta broadly clavate, barbed head almost as broad as long. Adanal setae widest in middle, blunt, barbed. Subcapitular mentum with medial carina in anterior third. Ventral plate irregularly foveolate. Lenticulus subrectangular, obviously longer than wide. Immatures with character states of the genus (below). Known only as Eocene fossil.

Description of adult. Measurements (gender not defined): total length: 492–543 μm (n = 12); notogastral width: 258–288 (n = 13).

Color: dark brown.

Cerotegument: Amorphous, blocky on notogaster and venter, mostly thick (up to 17–25 μm) on posterior margin ( Figs. 43, 44, 47 ); not found on lenticulus or prodorsum. Legs covered by smooth cerotegument, at least from trochanter to genu ( Figs. 8–11 ). Birefringence undetectable (see Discussion).

Integument: Notogaster, ventral plate and subcapitular mentum foveolate, with foveolae almost round (diameter 8–12 μm) on notogaster ( Figs. 1 , 28, 30, 31, 40, 48) and irregular on venter ( Figs. 2 , 33, 38, 39, 41, 49). Posterior to pteromorphs, notogastral margin with vertical ridges ( Figs. 2, 3 , 30, 49, 50, 57). Prodorsal surface, pedotecta, pteromorphs, and legs without foveolae, rough ( Figs. 1, 3 , 7–11 , 27, 29, 50). Lamellae ( Figs. 1, 3, 4 , 27, 29, 46, 48, 50) with irregular longitudinal ridges in lateral region. Transverse ridges on femora of legs ( Figs. 7, 9, 11 , 29).

Prodorsum: Lamella ( Figs. 1, 3, 4 , 27, 29, 43, 44, 46, 48, 50) broad, long, total length about 155 μm (n = 8), of which cusp about 90 μm (n = 7); cusps narrowly separated medially (largest distance between cusps about 7 μm, n = 5), each with tapered medial and lateral dens about 20 μm long (n = 4), on some specimens shorter ( Fig. 4 ). Rostral seta (ro) about 50 μm long (n = 6), smooth or with fine barbs, robust, tapered, borne on distinct cylindrical tubercle ( Figs. 2, 3, 5 , 46 ), mutual distance of pair about 120 μm (n = 4). Lamellar seta (le) about 50 μm long (n = 5), barbed, narrowly-phylliform, curved medially and ventrally, pair sometimes intersecting and/or lying on opposite lamella, borne at base of small longitudinal ridge which is situated more or less close to edge of medial incision ( Figs. 1, 4 , 29, 43, 44, 46, 48); mutual distance of pair about 50 μm (n = 7). Interlamellar seta (in) about 25 μm (n = 5), thick, subclavate, heavily barbed, ( Figs. 1, 3 ); mutual distance of pair about 65 μm (n = 8). Bothridial seta (bo) 40–50 (n = 8) μm long, clavate with somewhat flattened barbed head about twice longer than stalk ( Figs. 1, 3 , 43–45 ). Bothridium with undulating margin, detailed structure not observed ( Figs. 1, 3 , 45 ). Exobothridial seta (ex, Fig. 3 ) inserted posterior to bothridium, tapered, faintly barbed, about 12 μm long (n = 3). Dorsophragmata short, fused basally (Fig. 27, arrow).

Lateral region ( Figs. 3 , 37): With pair of narrow, nearly vertical (slightly curved posteriad) incisions in rostrum, just anterior to rostral setae ( Figs. 3 , 46 , arrow); pair framing subrectangular region about 50 μm wide (n = 2) ( Fig. 5 ), with narrow ridge running along each incision extending anteroventrad from near tutorium, bearing short cylindrical tubercle on which ro inserts ( Figs. 3 , 50 ). Tutorium (tu, Figs. 3 , 29, 46) smooth, about 95 μm long (n = 2); cusp tapered, knife-like, comprising about half total length of tutorium; pair strongly converging anteriorly (observed anteroventrally on damaged specimen, Fig. 29). Pedotectum I convex, extending from base of bothridium to epimere I and covering about one-third of femur I; not covering base of seta ex. Pedotectum II covering acetabulum II. Discidium present, merging with circumpedal carina (cp) posteriorly and bearing blunt, short (about 20 μm long; n = 3) custodium anteriorly ( Figs. 2, 3 ).

Notogaster ( Figs 1, 3 , 28, 30–32, 40, 48–50, 57): Longer than wide, ratio about 1:1.2–1.3. Lenticulus nearly rectangular, about twice longer than wide (85x 45 μm; n = 8). All notogastral setae thick, subclavate, heavily barbed; seta c about 19 μm (n = 7), l series about 20 μm (n = 7), h series about 22 μm (n = 7), p series about 16 μm long (n = 9). Setae directed as in Figs 1, 3 , 48, 50 . Lyrifissure im and opisthonotal gland opening (gla, Figs. 28, 40) situated as in Fig. 28. No other lyrifissures discovered, despite close observation of one fragment of cuticle containing h–p setal bases (Fig. 30). Narrow lateroposterior tectum present ( Figs. 49, 50 , 57 ).

Ventral region ( Figs. 2, 3 , 6 , 33, 38, 39, 41, 49, 59): Coxisternal setation 3–1–2–3 (n = 2). Epimeral setae thin, smooth, short (not longer than 15 μm; n = 5). Six (doubtfully seven on one specimen) pairs of genital setae ( Figs. 6 , 39); smooth, robust, about 5–10 μm long (n = 3). Aggenital seta (1 pair, Figs. 2 , 38) smooth, thin, 5 μm (n = 1); anal setae (2 pairs, Figs. 33, 41) smooth or slightly barbed, 7–10 μm, an 1 longer than an 2 (n = 3); adanal setae (3 pairs) barbed, thickened distally, ad 1 about 13 μm (n = 4), ad 2 about 11 μm (n = 4), ad 3 about 9 μm (n = 3) ( Figs. 2, 3 , 38, 41). Preanal organ includes pair of elongated, sclerotized rods connecting apodemal plate to respective anteromedial corners of anal valves ( Fig. 59 ).

Gnathosoma ( Figs. 2 , 49 ): Subcapitular mentum length about 70 μm (n = 6), width about 74 μm (n = 3); anterior margin rebordered, strongly reflexed as U-shaped ridge, with short medial ridge projecting posteriorly giving impression in ventral aspect of short inverted trident outlining pair of depressions. Setae h about 7 μm (n = 1), a, m about 7–15 μm (n = 2), all smooth, tapered. Palps and axillary region unobservable.

Legs ( Figs. 7–11 , 29): Heterotridactylous, with lateral claws spinose on dorsal surface and thinner than medial claw. Trochanters III, IV and all femora with porose areas on adaxial surface; tarsi with porose areas basiventrally. Femora with obliquely-transverse ridges on abaxial surface. Tibia IV appears to have dorsoabaxial groove. Some setae greatly enlarged, with thick rounded scales, including: ft" on tarsi II–IV, l", v" on tibiae II, l' on tibiae III–IV, l" on genua I–II and l' on genu IV. Seta l' on genu III long, tapered, almost smooth; other leg setae long, tapered, slightly barbed. Tarsus of leg I (not shown) without enlarged setae, tibia bears at least one on abaxial side. Solenidia ω1 and φ1 long, curved ventrad; other solenidia as in figures. Leg setal formulae (from trochanter to tarsus; not completely determined): leg I:? –5–3(1) –?–?; leg II:? –5–3(1)–4(1)– 15(2); leg III: 2–4–1(1)–3(1)–15; leg IV:?–2–2–3(1)–12.

Description of tritonymph ( Figs. 12–26 , 51–53 ). Measurements: length 448 μm, width 270 μm. A single specimen known.

Integument: light brown, most cuticle weakly sclerotized.

Prodorsum: Aspis with porose area present on prodorsum posterior to setae in, extending at least between these setae. Pair of flat, nearly straight, lamella-like ridges running obliquely posterolaterad from seta le to bothridium, connecting to series of transverse folds at level of setae in ( Figs. 21 , 51, 52 ). No conspicuous transverse carina in interlamellar region. Seta ro ( Figs. 13, 21, 22 ) about 35 μm long, slightly roughened on dorsal side, thick, blunt, strongly curved ventrad; mutual distance of pair about 25 μm. Seta le ( Figs. 14 , 25, 26 ) at least 40 μm long, borne on distinct tubercle, sword-like, tapered, barbed, bent ventrad; mutual distance of pair about 40 μm. Seta in ( Figs. 15, 21 ) about 15 μm long, heavily barbed, blunt, isodiametric or slightly widened distally. Seta ex ( Fig. 21 ) spine-shaped, smooth or slightly rugose, about 5 μm long. Bothridial seta (bo, Figs. 12, 21, 22 , 51–53 ) similar to that of adult: clavate with spinose head about as long as stalk and somewhat flattened, bent dorsad; length at least 35 μm.

Gastronotic region ( Figs. 21, 22 , 51–53 ): No small-scale cuticular sculpturing observable. With three large transverse plicae, each showing notable sclerotization and porosity in flat bottom of grooves; two lie posterior to setal pair da, one anterior to setal pair dp. Weaker folds occupy median part of dorsum, running obliquely toward posterior; folds virtually absent on subtriangular area posterior to setal pair dp. Humeral region (where setae c 2 normally occur) poorly observable, but one structure may represent remnant of seta c 2 (xa on Fig. 21 ). Setae of d series spindle-shaped, tapered, rough, about 12 μm long. Setae c 3 and l series ( Fig. 16 ) similar to those of adult, almost club-like, rough, blunt, stiff, about 15 μm long. Setae of h series ( Figs. 17–19 ) somewhat longer (h 2 longest, about 20 μm), more or less curved, barbed, blunt, isodiametric.

FIGURES 27–33. Scutoribates perornatus Sellnick, 1918 , adult, details. Samples MGCP Ar-6 (Figs. 27, 28), MGCP Ar-84 (29), MGCP Ar 42 (30–33). 27. Part of prodorsal cuticle with remnants of lamellae and dorsophragmata (indicated by arrow). 28. Dorso-lateral part of notogastral cuticle; combined image. 29. Prodorsum in fronto-ventral aspect; combined image. 30. Dorso-caudal part of notogastral cuticle; combined image. 31. Undetermined part of notogastral cuticle with nodule on inner face (indicated by arrow), combined image. 32. Same as 31, enlarged fragment. 33. Anal valves with left seta an 2 preserved. 28–31 are combined from 3–7 layers each. Scale bars: 27–31: 50 µm; 32, 33: 15 µm.

FIGURES 34–41. SEM images of cuticle fragments. 34–36. Scutoribates foveolatus ( Krivolutsky, 1974) . 34. Notogaster. Boxes indicate areas shown in next two figures. 35. Underside of the pteromorph, with cerotegument. 36. Internal face of notogaster with thickened nodule to which probable tendon or ligament attaches (arrow). 37. Same area in Unduloribates dianae Behan-Pelletier & Walter 2009 . 38–41. Scutoribates perornatus Sellnick, 1918 , adult, (sample MGCP Ar-6). 38. Part of ventral shield, custodium broken; arrow indicates circumpedal carina. 39. Genital valve, anterior at top; arrows indicate setae or their bases. 40. Fragment of notogastral cuticle with opisthonotal gland opening (gla) and setal base (h 3); anterior to top. 41. Anal region, right valve with seta an 1 preserved; anterior at top. Scale bars: 34, 38: 100 µm; 35–37, 39–41: 20 µm.

Ventral region ( Figs. 20, 22 , 53 ): With system of soft folds; medial margins of epimeral plates weakly defined, walls of apodemes I and II apparently porose. Epimeral, genital, aggenital, anal and adanal setae tapered, smooth or faintly rugose, about 5–7 μm long. Seta p 3 flattened, blunt, rugose on one side; p 2 flattened, widened distally, rugose; p 1 almost club-shaped, similar to that in adult ( Fig. 20 ). Large area of smooth, porose integument (probably sclerite) situated posterior to insertion of each leg IV, with gla opening in softer cuticle immediately laterad of this area. Only three genital setae seen, but five alveolae present on each side. Epimeral formula 3-1-2-3. One pair of aggenital, two pairs of anal, three pairs of adanal setae. Only cupules ips and ia seen with certainty; pair of small, bright spots (xb) and three slightly darkened spots (xc–xe) could represent four other lyrifissures but may be artifacts of preservation.

Gnathosoma: Rutellum (ru on Fig. 22 ) and chelate-dentate chelicera (che on Fig. 22 ) normal for Brachypylina , not pelopsiform. Palp (plp) poorly observable; several flagellate setae, probably of genu and tibia, seen on one side. Mentum poorly visible, dark elongated structure observed on left side may represent axillary saccule.

Legs ( Figs. 23–26 ): Covered with rough cerotegument; cuticle of femora and tibiae plicate. Monodactylous, claw bears paired line of minute spicules near dorsal contour. Proral setae on leg I shortest, smooth (probably eupathidial), subequal in length to unguinal setae on other legs. Solenidion φ1 and φ of tibia I and II (respectively) borne on large tubercle; solenidion φ2 of tibia I not on tubercle. Solenidia ω1 and φ1 of leg I subflagelate, curved; other solenidia shorter, more or less stiff. Solenidia ω1 and ω2 of leg II close to each other, as in adult. Setae l ' and l " on tibiae and genua I and II, and l ' on femur I and genu III enlarged, widened, covered with rounded scales or spines. Seta d on femora I and II, ev ' on femur IV, l ' on femur II, tibia III, genu and tibia IV, and ft " on tarsi II and III widened to lesser degree, roughened with scales or spines. Other leg setae more or less barbed; terminal setae on all tarsi with curved tips. Porose areas present on ventral side of femur III and proximoventrally on tarsus IV, unobservable on other legs and segments.

Designation of neotype for Scutoribates perornatus Sellnick, 1918 . The type specimen of Scutoribates perornatus designated by Sellnick (1918: 26) —№ 31 in the collection of the University of Königsberg—was probably destroyed after World War II (see above). Therefore, to fix the identity of this species by neotype selection we considered the eight existing specimens of the former collection of Fritsch, those that were studied and determined by Sellnick himself (1931). We hereby designate as the neotype of Scutoribates perornatus Sellnick, 1918 specimen № KMA 197-07 (originally № 7, Figs. 42–47 ) housed in the collection of the Kaliningrad Museum of Amber; a note to this effect has been added to the slide label. Though filled in with some transparent medium (presumably liquid paraffin in which Sellnick stored his materials (Sellnick 1927)) and dark (not shiny like the inclusions in dry amber samples), it is the best preserved and most observable of the eight specimens. The neotype allows observation of foveolate cuticle, apparent cerotegument, lamellae, all prodorsal and most notogastral setae, as well as pteromorphs and the general appearance of the ventral side (the latter seen through the inverted glass slide).

Figures

FIGURES 1 – 5. Scutoribates perornatus Sellnick, 1918, adult (1 – 3 – sample PIN 964 / 1152, 4 – 5 – sample MGCP Ar- 21). 1. Dorsal aspect. 2. Ventral aspect (legs not shown). 3. Lateral aspect (legs not shown, tutorium partly obscured); paired rostral incision indicated by arrow. 4. Asymmetrical lamellae with different cusp length and shape of seta le; oblique projection. 5. Rostrum with lateral incisions (indicated by arrows); oblique projection. Scale bars: 100 µm.

FIGURES 42 – 47. Proposed neotype of Scutoribates perornatus Sellnick, 1918 (KMA- 197 - 07, original number in Fritsch's collection: № 7). 42. Slide containing the specimen (before adding text to label: " Neotype: Sidorchuk, Norton 2010 "). 43. Ventral view of neotype. 44. Same, dorsal view. 45. Side of the specimen with four setae visible. 46. Anterior part of prodorsum with lamellae, tutorium (tu), rostral incision (arrow) and setae. 47. Posterior margin of notogaster with blocky cerotegument visible. Scale bars: 43, 44: 100 µm, 45 – 47: 50 µm; 43 – 46 are combined from 8 – 15 layers each.

FIGURES 6 – 11. Scutoribates perornatus Sellnick, 1918, adult (sample MGCP Ar- 84), details. 6. Genital valves; oblique projection, anterior at top. 7. Genu and femur of right leg I (tibia and tarsus destroyed, trochanter poorly visible). 8. Tarsus, tibia and genu of right leg II (femur and trochanter poorly visible). 9. Femur of left leg II (trochanter poorly visible). 10. Left leg III (ventral part of trochanter poorly visible). 11. Left leg IV (trochanter poorly visible). Scale bar: 50 µm.

FIGURES 48 – 56. 48 – 53 — Scutoribates perornatus Sellnick, 1918. 48 – 50, Adults. 48, 49. Specimens from Fritsch's collection. 48. Dorsal view of one of the best preserved specimens (KMA- 197 - 04). 49. Ventral view (KMA- 197 - 02). 50. Lateral view (sample PIN 964 / 1152). 51 – 53. Tritonymph (sample k- 2582). 51. Dorsal view of an air-filled specimen. 52. Enlarged proterosoma of the same specimen after 7 days maceration in mineral oil. 53. Lateral view. 54 – 56. Proposed neotype of Tectoribates parvus Sellnick, 1931 (KMA 197 - 24; № 24 in original Fritsch's collection:). 54. Dorsal view. 55. Ventral view. 56. Slide (before adding text to label: " Neotype: Sidorchuk, Norton 2010 "). Scale bars: 47 – 50, 53 – 55: 100 µm; 52: 50 µm. 48, 49, 54, 55 are combined from 3 – 15 layers each, 50 – 53 — from 52 – 87 layers.

FIGURES 57 – 60. 57. Posterior of hysterosoma of Scutoribates perornatus Sellnick, 1918 (sample PIN 964 / 1152), lateral aspect; arrow on presumed posterolateral tectum of notogaster. 58. Same area in lateral cross-section of Unduloribates dianae Behan-Pelletier & Walter 2009. 59. Preanal organ of S. perornatus as seen by transparency (ventral aspect, anterior to top); horizontal arrows point to pair of elongated support rods, vertical arrows to innermost apodemal plate (sample MGCP Ar- 84). 60. Interior view of same structure in highly cleared specimen of U. dianae; AN indicates anal valve. Scale bars: 57, 58: 20 µm; 59, 60: 50 µm; 57 is combined from 23 layers; 58 – 60 — from 3 – 4 layers each.

FIGURES 12 – 22. Scutoribates perornatus Sellnick, 1918, tritonymph (sample k- 2582). 12 – 15. Prodorsal setae. 16 – 20. Hysterosomal setae. 21. Dorsal view of tritonymph, legs not shown. 22. Same, lateroventral view (one anal valve with tear). Scale bars: 12 – 20: 50 µm; 21, 22: 100 µm.

FIGURES 23 – 26. Scutoribates perornatus Sellnick, 1918, tritonymph (sample k- 2582). Right legs I – IV (trochanters I and II not visible). Scale bar: 50 µm.