Caleremaeus arboricolus, Norton & Behan-Pelletier, 2020

Norton, Roy A. & Behan-Pelletier, Valerie M., 2020, Two unusual new species of Caleremaeus (Acari: Oribatida) from eastern North America, with redescription of C. retractus and reevaluation of the genus, Acarologia 60 (2), pp. 398-448 : 418-426

Caleremaeus arboricolus n. sp.

Zoobank: CF4D144D-15F3-467B-94DF-67104DB0C404

Etymology — The Latin species epithet ‘arboricolus’ is an adjective referring to the microhabitat (tree bark) of this species.

Material examined — Holotype adult and 35 adult paratypes from: USA, New York, Onondaga Co.; Syracuse, Oakwood Cemetery (43° 01.9 ஥ N, 76° 07.9 ஥ W); 10.ix.2008; R.A. Norton and D.A. Saunders, col., from mixed lichens on boles of living trees (washed and sieved). Ten adult paratypes from same location, but 24.vi.2019. One larva and 16 nymphs (non-type) from same two collections. Holotype and three paratypes deposited in USNM; five paratypes in CNC; remainder in RNC. Other material (all adults; in CNC and RNC) as follows. USA: Alabama: Baldwin Co., Bon Secours National Wildlife Refuge, Jeff Friend Trail (30º 14.6 ஥ N, 87º 47.21 ஥ W), 6.iii.1994, V. Behan-Pelletier, col., 9 from lichens on horizontal tree trunk. Maine: Penobscot Co., Orono, University of Maine Experimental Forest, x.1987, C. Stubbs col., 19 from lichens on red maple ( Acer rubrum Linn. ) trunk. New Jersey: Middlesex Co., New Brunswick, 1978, J. Walker col., 1 (no other data). New York: Essex Co., Newcomb, Huntington Wildlife Forest, H. Root, col., vii-viii-2002, 11 from lichens on sugar maple ( Acer saccharum Marshall ) [as Caleremaeus sp. 1 in Root et al. 2007]; Onondaga Co., LaFayette Experiment Station ( SUNY-ESF), 19.vii.1973, J. R. Philips col., 1 from regurgitated Great Horned Owl pellet in hardwood forest. Tennessee: Anderson Co., Great Smoky Mountain National Park, Indian Gap, 5200’ (elev.), 18.vi.1957, W. R.M. Mason col. Virginia: Page Co., Shenandoah National Park, Stony Mountain Trail, Skyland area, 4000’ elev., 14.viii.1986, E.E. Lindquist col., 1 from lichen mats on tree trunks and rocks. Canada: Ontario: Leeds-Grenville Co., Near Otter Lake (34º 34.87 ஥ N, 76º19.77 ஥ W), 23.vii.2003, J. Chen, V. Behan-Pelletier, J. Johnson col., 15 from cedar twigs (4m from ground), 5 from juniper twigs (<1m from ground).

Diagnosis — Caleremaeus species with adults having total length 311–353 µm. Prodorsum without distinct distal cusps; lamellar setae inserted on transverse ridge, each on slightly projecting tubercle; lamella represented by only indistinct apparent vestige; tutorium weakly developed; enantiophysis eA absent; oblique row of 2–3 knots in place of typical dorsosejugal tubercle. Notogastral setae conspicuous, erect, mostly thick and squamose, some with coating but without basal cerotegument nodule. Epimeral groove 2 usually without bordering tubercles or knots; ventrosejugal groove with only small, somewhat irregular and variable enantiophysis eS. Females and males consistently with five pairs of genital setae. Leg femora each with saccule. Nymphs with bothridial seta having squamose, flattened head, similar to that of adult; gastronotic seta h 1 thick, straight, squamose, pair distinctly diverging; exuvial scalps not reticulated in transmitted light.

Adult

Figures 8–11

Dimensions — Total length (n = 20) 311–353 µm (mean 332); maximum width 174–216 µm (mean 195). Female (n = 10) length 328–353 µm (mean 342), maximum width 174–216 µm (mean 204); male (n = 10) length 311–333 µm (mean 322), maximum width 181–191 µm (mean 185).

Integument, setae — Cerotegument excrescences ranging from dome-like to near-spherical nodules on short, thick stalk ( Fig. 10B ). Excrescences mostly 4–5 µm diameter on notogaster, closely spaced (mostly less than their diameter apart); dark, dense band of smaller excrescences (2 µm) around posterior and lateral notogastral margin; prodorsum and ventral plate with inconspicuous, small (1–2 µm) domes interspersed with dense, minute granules ( Fig. 10C ). Setae of various forms, but without conspicuous basal cerotegument nodule; some with pigmented coating (possibly cerotegument; e.g. Fig. 9 J–K).

Prodorsum — Central region foveate, with closely spaced circular depressions, mostly 6–8 µm diameter; foveation distinct between strong anterior transverse ridge and weakly-defined transverse ridge at level of acetabulum I ( Fig. 9A ). Lamella apparently vestigial, represented only by short, thin longitudinal carina. Without projecting cusp; setal pair le inserted on strong transverse ridge, each on distinct lateral tubercle ( Fig. 9 B–C). Interbothridial region with 2–3 knots (rarely one) in oblique transverse row on either side of central sigilla ( Fig. 9E ), sometimes with weakly-defined ridge parallel to row, between it and seta in ( Fig. 8A ). Submarginal crest ending anteriorly at seta ro; area between crest and rostral margin smooth, not scrobiculate ( Fig. 9G ). Rostral bulge moderately developed, without embossed pattern on ventral face ( Fig. 9H ). Tutorium weakly developed, gradually effacing both anteriorly and posteriorly; prodorsal enantiophysis absent. Lateral face highly sculptured ( Fig. 9G ): with several small tubercles or knots between bothridium and acetabulum I; with scalloped concentric carina or series of several short oblique ridges immediately anterior to parietal wall of acetabulum I. Variably foveate between pedotectum I and acetabulum II. With short transverse ridge above pedotectum I. Bothridium with anterior wall weakly foveate; posterior wall usually with one strong tooth (sometimes two) and 1–2 additional weak teeth or knots ( Fig. 9 D–E). Bothridial seta (50–60 µm; Fig. 9 D–F) flattened, with clavate outline seen face-on, distally rounded or slightly acute; head strongly pigmented, vaguely squamose, with low, narrow, blunt scales or mounds in linear, slightly radiating pattern; stalk smooth, not noticeably pigmented. Setae in and le short, distinctly barbed, pigmented and with isotropic coating; in (~ 12–15 µm), acuminate, le (15–25 µm) isodiametric to slightly clavate ( Fig. 9 B–C). Seta ro (20–27 µm) unpigmented, uncoated, with weak, inconspicuous barbs. Seta ex simple, minute (4–5 µm); vestige exv posteroventral to ex, separated by at least one alveolar width ( Fig. 9I ).

Notogaster — With 6–12 knots on anterior margin, mostly 5–7 µm diameter, often weakly defined ( Figs 8A , 9A ); humeral process relatively small, not projecting beyond anterior margin. About 12–15 strongly defined foveae (5–8 µm diameter) in transverse sulcus; otherwise without fovea or foveolae. Posterior bulge rather evenly tapered posteriorly; each lateral margin of bulge with nearly linear series of 8–15 knots or short ridges ( Figs 8A , 10A ). Setae of several types: lp, h 3, h 2 (25–30 µm) lightly pigmented, flattened, subclavate seen face-on, somewhat cupped and curved, with numerous conspicuous barbs on outer face and pigmented coating of variable thickness ( Fig. 9 J–K); h 1 similar but strongly curved mediad, mutual distance of pair equal to setal length or less; la, lm similar to lp but narrower, shorter (20–22 µm); seta c (12–15 µm) not broadened or only slightly so, and with little or no coating; p -row not broadened and without coating, p 1 (~ 25 µm) usually with strong, sharp point and few but strong barbs, p 2, p 3 very short (8–9 µm), spiniform, smooth or with 1–2 small barbs ( Fig. 9L ).

Venter and lateral podosoma — Epimere I foveate laterally; other epimeres without depressed features other than epimeral grooves and medial fossa on epimere IV, though strongly marked internal muscle sigilla often give reticulate impression in transmitted light ( Fig. 8B ). Development of coxisternal knots and tubercles somewhat variable: usually with several minute knots anterolateral to seta 2a and 2–3 others opposing them on epimere I across shallow epimeral groove 2; usually with small tubercle bearing seta 3c opposing 1–2 others across sejugal groove (comprising enantiophysis eS); knot or small tubercle sometimes present closely anterolateral to seta 4c; epimeral groove 4 with relatively small aggenital enantiophysis (e4) but without other tubercles or knots. Lateral region of epimeres III, IV without distinct coaptive ridge associated with leg trochanters. Without discrete discidium, but with distinct discidial ridge reaching anterodorsally to sejugal groove ( Fig. 9 ; dir), sometimes appearing like discidium in optical projection ( Fig. 8B ). Ventral setae simple, acicular, each inserting on small, low but distinct basal tubercle. Coxisternal setae 15–20 µm. Both genders consistently with five pairs of short (7–9 µm) genital setae; anal setae similar (10–12 µm). Adanal setae slightly longer: ad 1 (18–20 µm) posteriorly positioned, slightly shorter than mutual distance of pair; ad 2 similar, at posterolateral corner of plate; ad 3 shorter (10–12 µm), inserted about its length from plate margin, at level slightly posterior to middle of plate. Lyrifissure iad 6–7 µm long. Apophysis of preanal organ tubular. Ventral plate outline slightly bulging posteriorly between setal pair ad 1.

Gnathosoma — Subcapitulum without foveae, hypostomal (h, ~ 15 µm) and genal (a, m, 15–17, 20– 25 µm respectively) setae attenuate. Chelicera 75–80 µm long; without spicules; setae cha (~ 20 µm), chb (~ 15 µm) attenuate, barbed.

Legs — Femur I elongated, 4–4.5 times longer than maximum height in lateral view, with gradual transition between stalk and bulb, at distinctly oblique angle ( Fig. 11A ). Femur II ( Fig. 11H ) differently shaped: length only slightly more than twice height, with very short stalk, distinctly broader than that of femur I. All femora lacking surficial porose area but with short, broad saccule opening through short slit on proximal wall of bulb; saccule shape variable – simple, sausage-shaped or with irregular width ( Fig. 11 G–J). Trochanters III, IV with normal adaxial porose area. Genua and tibiae often with irregular dorsal contour due to several transverse ridges; genu and tibia I with enlarged seta l ஥, that of genu surpassing distal end of segment, that of tibia equal or greater than maximum tibia height ( Fig. 11E ). Tarsus I with slight projection mid-dorsally, bearing solenidia, famulus and seta ft ஧. Femoral seta d normal, acute, straight to slightly curved, without basal cerotegument nodule ( Fig. 11H ).

Juveniles

Figure 12

Length (without setae) and maximum width of larva (La) 196 x 92 µm (n = 1); protonymph 220 x 99 µm (n = 1); deutonymph 252–284 x 123–137 µm (n = 4); tritonymph (Tn) 294–319 x 157–167 µm (n = 2). Setae without conspicuous basal cerotegument nodule, but many with clear, basal isotropic sleeve, most conspicuous in small setae (e.g. Fig 12A , lp). Bothridial seta similar to that of adult: with distinct flattened head, clavate seen face-on, vaguely squamose ( Fig. 12J ). Seta ro conspicuous, projecting forward (~ 17 µm in La, 25 µm in Tn), longer than mutual distance of pair, acicular, weakly barbed, with inconspicuous coating near base; setae le, in and ex minute (~ 5 µm in La, ~ 7 µm in Tn), baculiform to acute, thickened by nearly complete isotropic coating, le of nymphs inserted on small tubercles. Larva with setae c 2, c 3 and dorsolateral series small, smooth, baculiform to acute, not or hardly emerging from clear sleeve ( Fig 12A ; lp). Middle row pigmented, with length and roughness increasing posteriorly, basal coating less conspicuous or apparently absent ( Fig. 12A ): c 1 (~ 5 µm), da (~ 12 µm) and dm (~ 15 µm) blunt, with one to several coarse barbs; dp (~ 25 µm) coarsely squamose with acute tip, slightly longer than mutual distance of pair; seta h 1 (~ 20 µm) directed straight posteriorly or slightly diverging, shorter than mutual distance, broadest and coarsely squamose in middle. Setae h 2 (attenuate, ~ 15 µm) and h 3 (acicular, ~ 5 µm) inserted close to paraprocts. Nymphs with gastronotal setae in c - and l -series small (8–12 µm in Tn), simple, baculiform to slightly tapered, extending little beyond coating. Nymphs with h 1 large (~ 80 µm in Tn), distinctly diverging, pigmented, slightly broadened and squamose in middle, distally blunt, setae and supporting posterior lobe upturned in deuto- and tritonymph but not protonymph ( Fig. 12C ); h 2, h 3 (25–30 µm in Tn) pigmented, coarsely barbed to squamose. Seta p 1 (30–40 µm in Tn) broadened and squamose in middle, distally blunt; p 2 (~ 15 µm in Tn) simple, acicular to acuminate. Ventral setae simple, acuminate to attenuate, with coating in basal half; in Tn epimeral setae 10–15 µm, genital and aggenital setae 8–10 µm, ad setae 10–12 µm, an 4–5 µm. Genital seta ontogeny consistently 1-2-4-5 (protonymph to adult). Ventral cuticle with microgranulate cerotegument, small excrescences often arranged in short lines ( Fig. 12H ). Ventral setae and those of basal leg segments short, simple, with full isotropic coating, sometimes displaced during preparation ( Fig. 12H, K ). Lateral setae on legs well developed, conspicuous; l ஥ of tibia I enlarged, coarsely barbed to squamose, extending distally well beyond end of segment ( Fig. 12J ); seta d of tibia I with distinct barbs and velum-like coating ( Fig. 12I ). Exuvial scalps not reticulated, ornamented only with surface plication ( Fig. 12A ); seta h 1 consistently retained on all exuviae.

Comparisons

Adults of C. arboricolus are distinguishable from those of all described extant Caleremaeus species in: having a prodorsum lacking enantiophysis eA and having the dorsosejugal tubercle (dt) represented instead by a linear series of usually three knots; having a notogaster with a series of knots outlining the posterior bulge and setae that are conspicuous, squamose (except p 2, p 3); and saccules on leg femora instead of porose areas.

The most similar described species is C. gleso , which is known only from Baltic amber. Based on Sellnick’s (1931) description and sketchy dorsal illustration of an adult, C. gleso shares with C. arboricolus the absence of distinct prodorsal cusps extending forward from a transverse ridge and notogastral setae that are clavate, at least in part. C. gleso differs from C. arboricolus in having: a prodorsum with larger, more clavate lamellar setae; a more sculptured central prodorsum (perhaps with more defined lamellae); and a depression on either side of the transverse sulcus. The notogaster was described as having foveate anterior and posterior bulges, but the sclerotized cuticle of these structures is smooth in all known extant species. Considering the difficulties of observing small amber inclusions, Sellnick may have mistaken the round cerotegument excrescences for ‘pits’, but this can be confirmed only if the species is rediscovered.

Figures

Figure 8 Caleremaeus arboricolusn. sp., adult: A – dorsal view (legs mostly omitted); B – ventral view (legs omitted). Scale bar: 50 µm.

Figure 9 Caleremaeus arboricolusn. sp., transmitted-light micrographs of adult: A – anterior third, dorsal view; B – transverse ridge and setae le; C – same, different specimen; D – bothridium and setabs; E – posterolateral area of prodorsum, dorsal view; F – head of bothridial seta; G – prodorsum, lateral view; H – same, deep focus optical section (insert on left = enlarged base of rostral bulge and rostrophragma); I – middle third of body, lateral view; J – notogastral seta h2; K – notogastral seta lp; L – notogastral setae p1 and p3; M – posterior view (setae h1, p1 broken from alveolus). Scale bars: 20 µm (A, G-I, M); 10 µm (B, C); 5 µm (D-F, J-L).

Figure 10 Caleremaeus arboricolusn. sp., transmitted-light micrographs of adult: A – part of series of knots at margin of posterior notogastral bulge; B – detached notogastral cerotegument (optical cross-section); C – ventral plate cerotegument (face-on) near setaag; D – coxisternum of male, surface focus (insert lower right = spermatopositor, arrowhead on largest alveolus); E – same, deeper focus; F – female with mostly extended ovipositor; G – distal part of ovipositor, showing ventral lobe (right) and one (of pair) dorsal lobe (left); H – coronal seta of ovipositor. Scale bars: 50 µm (F); 20 µm (D, E); 5 µm (A, B, G); 2 µm (C, H).

Figure 11 Caleremaeus arboricolusn. sp., transmitted-light micrographs of adult: A – legs I-IV, abaxial view (trochanter II not shown); B – base of femur I, abaxial; C – same, ventral view (arrow to partial retrotectum); D – trochanter III, ventral view (arrow to partial retrotectum), with base of femur (twisted); E – tibia and tarsus I, adaxial view (lower left insert =ft″ and base of solenidionω1 of different specimen); F – solenidionφ of tibia II; G – proximodorsal part of two femora I, showing variants of femur I saccule (arrow to stigma); H – femur II and partial genu, abaxial view; I – femur III, abaxial view; J – aggenital region and abaxial view of femur IV; K – trochanter and base of femur IV, abaxial view. Scale bars: 20 µm (A); 10 µm (B-E); 5 µm (G-K); 2 µm (F).

Figure 12 Caleremaeus arboricolusn. sp., transmitted-light micrographs of juveniles: A – exuvial scalp of larva, with inserts (top to bottom) of enlarged setaeda, dp, lp, h1; B – protonymph, pygidial region, dorsal view; C – deutonymph, lateral view; D – same, dorsal view; E – tritonymph, pygidial region; F – exuvial scale attachments, lateral view, with sclerotized pocket in underside of larval scalp (kp) on top, detached and nested cornicle k of proto- and deutonymph from same specimen on bottom; G – protonymph, ventral view; H – partial coxisternum of deutonymph, ventral view, anterior to right (insert = trochanter III seta v஬); I – dorsodistal tubercle of tibia I of deutonymph (lower) and tritonymph (upper: partial, better showing barbs and velum of setad); J – deutonymph, dorsal view of partial prodorsum and leg I (insert: coupled seta d and solenidion of tibia II); K – femur I setabvம of deutonymph, intact (left) and with isotropic external layer separated from birefringent core (right). Scale bars: 20 µm (A-E, G); 10 µm (H-J); 2 µm (F, K).