Eniochthonius Mahunkai Sp. N. (Acari: Oribatida: Eniochthoniidae), From North American Peatlands, With A Redescription Of Eniochthonius And A Key To North American Species Author Norton, R. A. Author Behan-Pelletier, V. M. text Acta Zoologica Academiae Scientiarum Hungaricae 2007 53 4 295 333 journal article 10.5281/zenodo.12585387 2064-2474 12585387 Eniochthonius mahunkai sp. n. Diagnosis. Adult relatively small (length 309–343 µm); notogaster moderately arched in lateral aspect. Bothridial seta slightly broadened and flattened distally, with 2–4 long tines and sparse small barbs. Notogaster obovate in dorsal aspect, with relatively long setae ( f 1 reaches insertion of h 1 in dorsal aspect). Aggenital region with three separate plates; seta ag inserted on smallest, middle plate. Leg tarsus setation (I–IV, famulus included) 18–15–13–13; each with it” present, it’ absent. Adult ( Figs 1–35 , 51A ) Dimensions (n = 20). Mean total length 325 µm (range 309–343 µm); mean maximum width 154 µm (range 147–162 µm). Mean length/width ratio of individual specimens 2.11 (varies with degree of distension); proportions of total length of fully distended specimen contributed by prodorsum 0.35; by soft, pleated sejugal band 0.04; and by hysterosoma 0.61. When fully contracted or distended, alignment of protero- and opisthosoma nearly linear ( Figs 2 , 51A ). Integument. In reflected light mostly smooth, shiny, pale brownish-yellow; epimeral borders, apodemes, grooves and overlapping edges of sclerites appear darker. Notogaster with two conspicuous dark transverse bands: anterior derives from sulcus (see below), posterior band derives from thickened anterior border of pygidium, showing through tectal limb of scissure by transparency. Cerotegument apparent only as small patches of granular excrescences, inconspicuous except in SEM ( Figs 12–13 , 20–21 ), distributed as indicated below. Most regions with irregular shallow grooves or wrinkles, hardly noticeable except in SEM ( Fig. 13 ). Except as noted, epicuticle of cuticular plates with continuous pattern of small, highly refractive chambers, giving irregular, falselyporose appearance in bright-field illumination, both before and after demineralization ( Fig. 18 ; see Note 1). Chambers on legs 2–3 times as large as those on body ( Fig. 17 ); most chambers on genital plates elongated, directed obliquely ( Fig. 16 ). General cuticle pale brown after demineralization, giving evidence of light sclerotization. Setae evenly birefringent throughout length. Prodorsum . Roughly triangular in dorsal aspect, with slight constriction at level of lamellar setae ( Figs 1 , 12 ). Lateral prodorsal margins undulating; two concavities form niches accommodating legs I and II, respectively, with small flange between them ( Fig. 2 ); more distal concavity delimits rostral lobe, best seen in anterior aspect ( Fig. 15 ). Rostrum with smooth, slightly reflexed margin ( Fig. 14 ). Cuticle thicker in vague groove between bothridia ( Fig. 24 , arrowhead), giving appearance of darker band connecting bothridia in transmitted light ( Fig. 1 ), bearing sigilla for cheliceral retractor muscles. Cuticle thinner posterior to groove, where prodorsum narrows slightly, telescoping into hysterosoma, but posterior margin strongly thickened where it attaches to soft sejugal cuticle ( Figs 23, 24 ). Interlamellar ( in ), lamellar ( le ) and rostral setae ( ro ) setae attenuate, with sparse minute barbs on outer curvature; respective lengths ca. 40, 35 and 30 µm; respective mutual distances of pairs 44, 30 and 20 µm. Setae in and le usually erect, slightly curved posteromedially and anteromedially, respectively; seta ro strongly curved at base, directed posterodorsally (all can be deformed during preparation). Two exobothridial setae finely attenuate; xa closely lateral to bothridium, ca. 33 µm, directed anterodorsally; xp posteroventral to xa , ca. 24 µm, directed ventrally ( Fig. 2 ). Bothridium opening on distinct swelling ( Fig. 13 ); with three chambers, outer two with smooth walls, inner one densely spiculate ( Fig. 29 ; see Note 3). Bothridial seta ( bo ) slightly broadened and flattened distally, with 2–4 long tines (ca. 10 µm) and sparse small barbs ( Figs 1 , 13 ); length ca. 65 µm, about equal to mutual distance of bothridial apertures. Notogaster ( Figs 1, 2 , 12 ). Roughly obovate in dorsal aspect, anteriorly about same width as prodorsum; 1.3–1.5 times longer than maximum width (slightly posterior to mid-length), depending on distension; moderately arched in lateral aspect, confluent with curvature of prodorsum ( Fig. 51A ). With anterior plate (pronotaspis, NA) bearing setal rows c , d and e ; isolated from pygidial region (PY) by single transverse tectiform (type-L) scissure; tectum ca. 20 µm wide (of which solid limb ca. 15 µm) in sagittal plane, decreasing laterally to end at suprapleural plate ( sp ); difficult to discern in dorsal aspect of whole specimens as posterior border extremely thin ( Figs 1 , 26 , bt ). In contracted specimens, anterior margin of pygidium ( bp ) telescoping underneath tectum to level ca. 20 µm anterior to seta e 1 . Transverse sulcus of pronotaspis emphasized in transmitted light by slightly thicker cuticle ( Figs 1 , 25 ), weakest medially, between setal pair d 1 . Pronotaspis isolated from pleural region (PL) by paired elongated suprapleural plate (ca. 15 times longer than wide), extending anteriorly from about level of setal row f to within about 10 µm of sejugal articulation; plate ca. 125 µm long, 10 µm at widest point, bearing setae h 2 , h 3 in posterior quarter ( Fig. 2 ); h 3 reaches posterior end of plate, h 2 extends well beyond it. Pleural region with narrow, laterally projecting carina originating near level of seta c 3 and merging posteriorly with notogastral margin, just posterior to level of legs IV; in anterior half, ventral surface of carina invaginated as taenidium ( Figs 30–32 ). Posterior to leg IV taenidium curves ventrad, away from pleural carina; continuing as short, shallow groove onto aggenital plate (see below). Hidden arched wall of taenidium bearing inconspicuous elongated porose area (ca. 25–30 µm long; see Note 4) in region dorsal to legs III and IV ( Figs 2 , pa ; 33); rarely two widely separated smaller porose areas present instead. Lateral margin of notogaster sharply folded dorsomediad in posterior two-thirds to form plicature plate ( Fig. 3 , pp ), hidden in contracted specimens (see Note 5); plicature plate not mineralized, without epicuticular chambers. Five pairs of lyrifissures present (see Note 6); ia slit-like, inconspicuous, aligned with edge of pleural carina and lying between it and porose area ( Fig. 33 , arrowhead). Others with cupular form ( Figs 2, 3 ): im posterolateral on pronotaspis, about 10 µm from its lateral edge; ip far anterior in pleural region near posterior end of pleural carina; ih approximately aligned between im and seta p 3 , about 30 µm from the latter; ips on plicature plate about at level of seta ad 3 . Notogastral setae mostly attenuate, posteriorly directed, slightly curved, with minute serration of barbs dorsally, difficult to see except in profile ( Fig. 35 ). Setae mostly 40–55 µm long; when flattened by coverglass many reaching level of insertions for next most posterior row; e 2 and p 1 longest, latter extending slightly beyond posterior margin in dorsal aspect; seta c 3 much smaller (ca. 15 µm), finely attenuate and flexible, inconspicuously inserted in anterolateral corner of pronotaspis ( Figs 1 , 13 ). Coxisternum . Epimeres I and II fully fused, ca. 80 µm wide; most of surface with granular cerotegument ( Fig. 21 ) inconspicuous in transmitted light due to epicuticular chambers. Epimere II bending abruptly dorsad just posterior to seta 2a , then again posteriorly, prior to joining soft articulat- (50 µm) Figs 1–3. Eniochthonius mahunkai sp. n. , adult (contracted specimen): 1 = dorsal aspect; 2 = lateral aspect; 3 = ventral aspect. Legs and gnathosoma partly shown (1, 3) or omitted (2). All to same scale Figs 4–8. Eniochthonius mahunkai sp. n. , adult: 4 = leg I, femur, genu and tibia; 5 = leg I, tibia and tarsus; 6 = leg II, except trochanter; 7 = leg III; 8 = leg IV. All abaxial view; all to same scale (50 µm). Unlabeled setae include: proral pair ( p ) inserted dorsally at base of claws on all legs; two setae on reverse side of Fig. 5, indicated only by dotted circles: a’ and tc’ (respectively below and above seta a” in figure); and several others on Figs. 6 and 8 that can be interpreted from Figs 4 and 7 , respectively. ing sejugal cuticle, forming “neck” in proterosoma that inserts into hysterosoma during contracted state ( Figs 2 , 23, 27 ). Sub-cruciform pattern of narrow grooves on surface ( Fig. 21 ) overlying well formed apodeme 2 and anterior sternal apodeme; latter ending posteriorly at change in contour. Supracoxal gland opening at dorsal margin of epimere I, at level of epimeral seta 1a ; cuticle along canal border projecting internally in row of small teeth for about 15 µm anterior to aperture. Supracoxal seta eI ca. 5 µm, spiniform, nearly isodiametric but with minute terminal fork; inserted immediately dorsal to trochanter I, below podocephalic canal. Epimeres III and IV fully fused with each other, ca. 90 µm wide; surface with weak grooves and cerotegument granules marking positions of underlying apodemes ( Fig. 21 ). Epimere IV also fully fused to anterior aggenital plate. Posterior sternal apodeme conspicuous, about 30 µm long, ending posteriorly about at level of seta 4b . Apodeme 3 short, reaching at most halfway to midline; apodeme 4 absent ( Fig. 3 ). Articulations with leg trochanters sunken, no soft cuticle exposed, approaching ball-socket formation. Epimeral setal formula 3–1–3–4; setae finely attenuate, apparently smooth, mostly 10–15 µm; seta 1a slightly longer (ca. 20 µm), with inconspicuous barbs. Anogenital region. With three pairs of mutually articulated aggenital plates that collectively bracket the genital and preanal plates ( Fig. 3 ). Anterior plate largest, roughly triangular, ca. 40 µm long, imperceptibly fused to epimere IV, with two well marked impressions; medial one (close to genital plate) broad, shallow; lateral one (postpedal fossa fo ) behind leg IV insertion, narrow with well-defined aperture ( Figs 2 , 21 ). Vague, shallow groove extending laterally from fossa towards pleural region of notogaster, aligned with pleural taenidium ( Fig. 31 ). Middle aggenital plate small, 4-sided polygon, ca. 22 µm in longest dimension; bearing seta ag (simple, ca. 12 µm). Posterior aggenital plate narrowly sub-rectangular, slightly wider posteriorly, ca. 35 µm long. Genital plates roughly pentagonal as pair, each truncated posteriorly; large, ca. 90 µm long, 55 µm at widest point; narrow band of unsclerotized cuticle cutting transversely (slightly obliquely) across plate at widest point and meeting articulation between second and third aggenital plates laterally; band evident by bars: 20 µm (9), 10 µm (10), 25 µm (11). Figs 9–11. Eniochthonius mahunkai sp. n. , adult: 9 = subcapitulum, ventral aspect (* marks position of postpalpal setae on dorsal face); 10 = chelicera, adaxial aspect; 11 = palp, abaxial aspect. Scale lightness in transmitted light, chambered epicuticle above it remaining mineralized, but in pattern different from that of surrounding epicuticle ( Fig. 16 ); with sparse cerotegument granules anteriorly ( Fig. 21 ). Ten pairs of genital setae forming two longitudinal rows, seven in medial and three in lateral; four medial and one lateral seta anterior to transverse band; spacing of medial row setae slightly variable; setae attenuate, without noticeable barbs, 12–15 µm. Ovipositor strongly pleated, short, only ca. 30 µm long when folded (just proximal to terminal lobes); directed posteroventrad when in body ( Fig. 23 , ov ), so that paired dorsal lobes in ventral position; with nine pairs of setae: τ 1 and Ψ 1 ca. 35 µm; τ 2–4 , Ψ 2 and three pairs of coronal setae 13–15 µm; all setae eupathidial. Genital papillae rela- Table 1. Ontogeny of setae and solenidia in Eniochthonius mahunkai sp. n. (Structures are indicated where they are first added and are present through the rest of ontogeny; setae in parentheses repre- sent pairs; dash indicates no additions. See text for variation) Figs 12–18. Eniochthonius mahunkai sp. n. , adult: 12 = dorsal habitus; 13 = bothridial seta ( bo ) and sejugal region, dorsolateral aspect; 14 = rostrum and distal region of subcapitulum, lateral aspect; 15 = proterosoma, partial anterior view; 16 = genital region in polarized transmitted light (* marks location of different mineralization pattern covering narrow transverse band of unsclerotized procuticle that divides genital plate); 17 = mineralization pattern on leg III; 18 = mineralization pattern in central notogaster, polarized light on left, unpolarized on right. Figs 12–15 scanning electron micro- graphs; 16–18 light micrographs. Scale bars: 50 µm (12), 10 µm (13–15), 20 µm (16–18). tively large (10–12 µm diameter), all three similar. Preanal plate ( Figs 22 , 28 , pr ) narrow, ca. 45 µm across, may be inconspicuous in contracted specimens. Collectively, anal and adanal plates ca. 60 µm long, 50 µm wide anteriorly, tapering posteriorly to 20–25 µm wide at level of seta ad 1 ; without noticeable cerotegument. Three pairs of adanal setae 15 µm, two pairs of anal setae 15 µm; all attenuate, smooth. Anteromedial margin of each anal plate projected internally as contiguous pair of solid, horn-like, heavily sclerotized anal apodemes ( Fig. 28 , aa ), conspicuous in transmitted light. Legs ( Figs 4–8 ). Legs all relatively short, similar in size, ca. 0.35 to 0.40 times body length, IV longest; simple in structure, without bosses, tubercles or surface sculpturing other than fine, wrinkle-like grooves running obliquely to transversely across segments. Basally, segments with constriction near articulation; constriction strongest dorsally on femora, ventrally on more distal segments, and only weakly defined on tarsi III–IV. Articulations tight, almost ball-socket type , without clearly defined protecta, but soft articulating cuticle not exposed, even ventrally, regardless of degree of flexing. All trochanters, and femora I and II, with cerotegument granules. All tarsi with normal, proximodorsal lyrifissure. Single claw simple in structure, without barbs or dentition. Leg setae attenuate to sub-flagellate, mostly smooth or with sparse, minute barbs; seta a’ on tarsi I and II with several strong barbs (not illustrated). Setation (legs I-IV, including famulus but not solenidia) of trochanters (0–0–2–2), femora (3–5–3–3), genua (5–3–3–3), tibiae (5–4–3–3), tarsi (18–15–13–13); no variation noted (but slight variations in ontogeny, described below); setal homologies given in Figs 4–8 and in Table 1 (see also Note 11). Seta d of tibiae I and II minute, coupled to respective solenidion ϕ, in adjacent but separate alveoli; seta d of tibia III and of all genua independent of respective solenidia. Solenidial formula (legs I–IV) of genua (2–1–1–1), tibiae (1–1–1–0), tarsi (3–1–0–0). Genual solenidia all piliform; σ”I proximal to seta d , σ’ I approximately lateral to it; σII placed like σ”I, slightly on posterior face; σ of genua III and IV also slightly on posterior face, but well distal to seta d . Tibial solenidion ϕI tactile (flagellate, ca. 70 µm), directed dorsodistally, about half length of leg I; solenidion ϕII ceratiform, slightly shorter than segment length, strongly curved toward posterior face; ϕIII piliform, with form and position similar to σIII, distal to d . Tarsal solenidion ω1 large, ceratiform, curved toward segment, and ending directed toward base of claw; ω2 and ω3 piliform, closely aligned together, lateral to famulus on posterior face; ω of tarsus II similar to ω1 of tarsus I, but slightly smaller. Famulus ( e ) aligned between seta ft’ and solenidion ω2; forked: one branch thick, terminating bluntly or with slight knob-like swelling, other attenuate, bract-like, about onethird longer ( Fig. 5 ). Gnathosoma . Subcapitulum anarthric but with paired pattern of wrinkles and grooves leading posterolaterally from inferior commissure of mouth (in normal position of labiogenal articulation; see Note 14), delineating region of triangular mentum from paired genae ( Figs 9 , 20 ); cerotegument granules small, vague, restricted to periphery. Dorsal surface of genae with extensive, paired, rasp-like region. No dentition observed on labrum. With small, rectangular capitular apodeme, ca. 10 µm wide, projecting 15 µm posteriorly from subcapitular cervix. Rutellum ( Fig. 9 , RU) narrow, seemingly inserted in genu like large seta, slightly broadened distally with three obliquely aligned terminal teeth (see Note 7). Four setae on subcapitular face, positioned as in Fig. 9 ; all attenuate, with several minute barbs; hypostomal seta ( h ) 15 µm, median setae ( m 1 , m 2 ) 17 µm, anterior seta ( a ) largest (23 µm) and less rapidly tapered than others. Three heterogeneous adoral setae on exposed lateral lips: or 1 and or 3 attenuate, without ornamentation, ca. 8 µm and 20 µm respectively. Seta or 2 complex ( Figs 9 , 14 , 20 ): main axis (ca. 24 µm) finely attenuate, with small ventral tooth at mid-length, distal half bent strongly dorsad (slightly bowed like parenthesis) then again anteriorly for short distance; vertical portion of or 2 pectinate with more than 10 long, fine, closely adjacent, medially directed cilia, which (as setal pair) interdigitate to form baleen-like sieve. Postpalpal seta 7–8 µm, little tapered, terminating in distal fork; attached without alveolus, and at near right-angle, to vertical post-like tubercle about as long as and little wider than seta ( Fig. 34 ). Palp simple, all five segments fully articulated; others by proportion. Figs 19–22. Eniochthonius mahunkai sp. n. , adult: 19 = ventral habitus; 20 = subcapitulum and vicinity, ventral aspect (white arrowhead indicates fused pair of ultimal setae, * marks groove separating gena and mentum); 21 = coxisternum and vicinity, ventral aspect; 22 = anogenital region and adjacent notogaster (AD, AN indicate adanal and anal valves, respectively; G marks position of narrow transverse band of unsclerotized procuticle that divides genital plate). Scale bars: 50 µm (19), 10 µm (20); 20 µm (21, 22). Figs 23–28. Eniochthonius mahunkai sp. n. , adult, lateral aspect of near-sagittal section, anterior to left: 23 = overview of section, with position of enlarged images marked by respective figure number in similar relative position (ch = chelicera, fb = food bolus, ov = ovipositor); 24 = dorsal sejugal region (sej = soft articulating cuticle, arrowhead indicates thickened cuticle behind which proterosoma narrows slightly to proximal “neck”); 25 = region of transverse sulcus, showing thickened cuticle and overlying chambered epicuticle (demineralized, marked with arrowhead); 26 = telescoping transverse scissure (type-L), showing tectum on pronotaspis (asterisks mark limits of sclerotized cuticle on respective plates; voluminous connecting soft cuticle not shown); 27 = ventral sejugal region (* marks cuticle of proximal “neck”, exposed only in distended individuals); 28 = juncture of genital, preanal (pr) and anal plates (aa = anal apodeme; gp = posterior genital papilla). Scale bar: 50 µm (23), Figs 29–35. Eniochthonius mahunkai sp. n. , adult: 29 = bothridium, optical section (arrowhead indicates spiculated inner chamber); 30 = anterior region of isolated suprapleural plate (sp) and pleural region of notogaster (pl), lateral aspect (cf. Fig. 2), showing taenidium (t) curving ventrad (* and IV mark approximate positions of postpedal fossa on aggenital plate and leg IV insertion, respectively); 31 = taenidium (t) and fossa (fo) on left side, showing curved alignment seen by transparency on dorsally positioned, slightly flattened specimen (III = leg III, * marks approximate level of section in Fig. 32); 32 = frontal section through notogastral taenidium and porose area (t = taenidium, sa = sternal apodeme of epimere III, tr III = trochanter III, arrow marks open slot of taenidium); 33 = notogastral taenidium and porose area, lateral aspect (cf. Fig. 30), at three progressively deeper focal planes (arrowhead indicates lyrifissure ia ); 34 = posterodorsal corner of subcapitulum, lateral aspect, showing forked postpalpal seta (P = femur of palp, arrowhead indicates cylindrical stalk on which seta inserts at strong angle); 35 = notogastral seta e 1 , showing fine barbs. All but Fig. 31 with differential contrast transmitted illumination; 30 and 34 layered images. Scale bars: 50 µm (30), 20 µm (31, 32), 10 µm (29, 33–35). femur and tarsus approximately of equal length, about twice that of genu and tibia ( Fig. 11 ). Setation (trochanter to tarsus) 0–2–1–3–11, plus solenidion ω. All setae on femur to tibia and most setae on tarsus attenuate, with sparse minute barbs; unpaired anteroculminal, acm , and ultimal pair ( ul ) of tarsus eupathidial, little tapered; ultimal pair fused near base to form strongly diverging fork; v 1 ” spiniform. Solenidion ω about half length of tarsus, narrowly ceratiform, curved toward tip of segment to end near ultimal fork ( Figs 11 , 20 ). Chelicera ( Fig. 10 ) relatively narrow, ca. 65 µm long, 22 µm greatest width, gradually tapered distally; small proximal portion (less than one-tenth of length) internalized through cheliceral frame (body wall). Not mineralized. Ventral trochanter remnant relatively large, extending about half length of chelicera. Main cheliceral body with fine longitudinal striae dorsally (not illustrated), proximal to seta cha ; adaxial face with several scattered sharp spicules. Digits ca. 21 µm long, tapered to fine tips, each with four teeth; abaxial face of fixed digit with small, seemingly porose region of unknown nature; small, sharp mid-ventral tooth near base of movable digit. Setae inserted as in Fig. 10 ; cha , chb ca. 7 µm, 16 µm respectively. Ontogeny ( Figs 36–50 ) Dimensions . Mean (range) total length and maximum width measured from 10 specimens of each instar: larva (La): 218 µm (208–230 µm) by 97 µm (93–108 µm); protonymph (Pn) 247 µm (230–260 µm) by 113 µm (105–118 µm); deutonymph (Dn) 279 µm (259–289 µm) by 126 µm (118–132 µm); tritonymph (Tn) 310 µm (294–323 µm) by 146 µm (132–157 µm). As in adult, length varies widely depending on degree of distention; width varies also, being slightly narrower in distended specimens. Integument . Shiny in reflected light; nearly white in early instars, may have slight yellow tint in nymphs, but always paler than adult. Except at articulations, with strongly chambered, mineralized cuticle in all immature instars, essentially like that of adult; when demineralized, chambers more discernable in nymphs than in larva. Prodorsum . General structure similar to that of adult, except lateral margin rather simple in La; distinct rostral lobe and concavities for legs appear in Pn. Posterior margin of prodorsum not noticeably thickened in any immature instar. Setation generally similar to that of adult, but setae in and le acicular and more clearly barbed in La, becoming attenuate in nymphs. Posterior exobothridial seta ( xp ) proportionally smaller than in adult; about one-quarter length of anterior ( xa ). Bothridial seta distally broadened and barbed; number of long tines 0–2 in La ( Fig. 43 ) and 0–4 in nymphs. Bothridium two-chambered in all immature instars, with inner chamber densely spiculate. Gastronotic region . Larva with notogaster divided into three parts – pronotaspis (NA), mesonotaspis (NM) and pygidium (PY) – by two simple, type-E transverse scissures ( Fig. 36 ). Anterior scissure, between setal rows d and e (scissure ar 2 of GRANDJEAN 1947 ) with relatively broader articulating cuticle; posterior scissure, between rows e and f ( ar3 ), very narrow. Scissures reaching laterally to broad, soft, striated pleural band bordering notogaster. Neither suprapleural plate nor plicature plate developed; without distinct pleural carina. Single small, oval porose area (ca. 6 µm long) on vague pleural extension of pronotaspis, posteroventral to seta c 3 ( Fig. 44 ). With 13 pairs of setae representing typical holotrichous setation ( Fig. 36 ). Setae heterotrichous: c 1 , c 2 , and d 1 acicular and more clearly barbed than in other instars ( Fig. 42 ); cp variable (acicular, attenuate or intermediate); f 1 thickest of all notogastral setae, acicular with dorsal row of inconspicuous fine barbs; c 3 attenuate but relatively longer than in nymphs and adult (longer than acicular setae) ( Fig. 37 ). Lyrifissures cupular: ia on lateral margin of pronotaspis, about 15 µm anterior to scissure; im near lateral margin of mesonotaspis; ip far anterior from usual position (see Note 6), ca. 15 µm posteroventral to im and 5 µm from notogastral border. Figs 36–41. Eniochthonius mahunkai sp. n. , immatures: 36 = larva, dorsal aspect; 37 = same, ventral aspect (specimen contracted, legs incomplete); 38 = opisthosomal venter of distended larva (adapted from GRANDJEAN 1933 ), contrasting presence of inguinal seta h 4 in E. mahunkai (left side) with its absence in E. minutissmus (right side); 39 = tritonymph, dorsal aspect; 40 = same, ventral aspect (legs incomplete; apa = anterior porose area); 41 = schematic dorsal view of left tarsi III (top) and IV (bottom) at instars indicated, anterior (‘) face to right, distal at top (La = larva, Pn = protonymph, Ad = adult); setal insertions indicated by circles: black = dorsal position, visible directly (half-circles are lateral); dotted = ventral position, by transparency). Scale bars: 50 µm (36–37, 39–40), 10 µm (38). Nymphs with notogastral structure similar to that of adult in having single transverse scissure immediately posterior to setal row e (i.e. pronotaspis carries setal rows c-e ; Fig. 39 ) and suprapleural plate, bearing setae h 2 , h 3 , but with soft, striated cuticle between notogaster and coxisternum. Suprapleural plate shorter and broader (6–7 times longer than broad) than in adult, reaching anteriorly only to level of leg IV. Transverse scissure without tectal limb, but pronotaspis cuticle bends sharply ventrad at level of row e , forming narrow vertical wall ending at very narrow, hinge-like articulation with pygidial region ( Fig. 46 , arrowhead); anterior sclerite therefore higher than posterior one in lateral aspect, but without ability to telescope. Indistinct groove present posterior to setal row d (remnant of ar 2 ), less conspicuous than homologous transverse sulcus of adult. Pleural region with porose area similar to that of La, lying between seta c 3 and anterolateral corner of pronotaspis. Pleural carina present but weakly developed; with second oval porose area ( app ) on underside ( Fig. 45 ; see Note 4); in dorsoventral aspect, porose area appears between levels of legs III and IV. Cupule ia between porose area and anterior corner of suprapleural plate; im dorsal to latter plate; ip further anterior in pleural region than in La, approximately as in adult; ih anterodorsal to seta p 3 , as in adult. Ventrolateral plicature plate develops posteriorly in Pn, fully formed (as in adult) in Dn and Tn; contains cupule ips as in adult. All nymphs with 16 pairs of setae, representing larval complement plus pseudanal setae p 1 -p 3 ( p 4 absent from nymphs and adult; see Note 8). All notogastral setae with dorsal barbs, usually inconspicuous. Setae of nymphs all attenuate as in adult and with similar relative size. Coxisternum . Soft cuticle between epimere I and subcapitulum granular. All epimeres with medial band of soft, longitudinally striated cuticle; more apparent in La ( Fig. 37 ) since band folds more deeply in nymphs ( Fig. 40 ). Sejugal articulation with transverse striae, blending into those of epimera II and III, respectively, in dactylographic pattern. In all immatures, each half of epimere I at least weakly fused to respective half of epimere II; separated by conspicuous groove, but without apparent articulation. In nymphs, halves of epimeres III and IV fully fused, with no external or internal delimitation. Postpedal fossa absent from all immatures. Larval Claparède’s organ of typical form, without indication of annulations; seta 1c scale-like, reverting to normal form in Pn. Otherwise, epimeral setae relatively short, attenuate, smooth or with sparse, minute barbs; generally similar in form and relative size to those of adult. Setal ontogeny as follows: La (3–1–2), Pn (3–1–2–1), Dn (3–1–3 –3), Tn (3–1–3–4); in Fig. 40 setae of epimere IV lettered in order of appearance (a in Pn, b, c in Dn, d in Tn); in two of 11 tritonymphs examined, seta 4d absent unilaterally. Anogenital region. Genital region of larva represented by broad expanse of soft, longitudinally striated cuticle ( Fig. 37 ), except for pair of conspicuous thorn-shaped, sclerotized, laterally flattened preanal spines projecting posteroventrad ( Figs 49, 50 ; see Note 9); nymphs without spines. Genital valves relatively larger in successive nymphs; setation (Pn-Tn) 1–3–7, with Tn having 3 setae in lateral row, 4 in medial row ( Fig. 40 ). Aggenital plates absent. Aggenital seta first forms in Tn (often unilaterally; see Note 10) or adult; if in Tn, it inserts at extreme lateral edge of genital plate ( Fig. 40 ). Preanal plate absent from all immatures. All immatures with apodeme extending internally from anterior walls of paraproctal valves ( Figs 49, 50 ; aa ): with dark V-shaped cross section in ventral aspect (“V” pointed anteriorly), subtriangular in lateral aspect. Paraproctal valves of La (segment PS) narrow, well defined, consistently with 4 pairs of setae arranged in uniformly spaced row ( Fig. 38 , left side). Cupule ips not present on paraprocts; ih in soft cuticle between most anterior pseudanal seta (inguinal seta p 4 ) and notogastral seta h 3 . Inguinal seta h 4 present near anterior end of paraprocts on opposite side of cupule ih from h 3 (transcupular) ( Figs 37, 38 ). Both p 4 and h 4 lost from all later instars (see Note 8). Paraproctal setation 4–3–2–2 (La-Tn); without paraproctal atrichosy. Adanal and anal plates acquire adult form and setation in Dn. Legs . General form and proportions similar to those of adult, but articulations with soft cuticle exposed, clearly broader ventrally, as typical for oribatid mites. Ontogeny of setae and solenidia given in Table 1 ; their forms and positions generally as in adult, except as noted below. No variation Scale bars: 10 µm (43, 45, 47–49), 5 µm (42, 44, 46, 50). Figs 42 and 44 layered images. Figs 42–50. Eniochthonius mahunkai sp. n. , immatures: 42 = notogastral seta c 1 of larva; 43 = bothridial seta and interlamellar seta ( in ) of larva, near-dorsal aspect; 44 = humeral region of larval notogaster, lateral aspect, showing porose area (arrowhead) and seta c 3 ; 45 = same, but tritonymph with pleural carina bearing posterior porose area (app) and cupule ia on underside seen by transparency (apa = anterior porose area); 46 = sagittal section of tritonymph notogaster at transverse scissure (anterior to left; arrowhead indicates extremely narrow articulating cuticle); 47 = subcapitulum of tritonymph, ventral aspect in polarized light, showing lack of demineralization in mentum; 48 = partial tarsus I of tritonymph, lateral aspect, showing famulus (e); 49 = posteroventral region of larval opisthosoma, lateral aspect, showing preanal spine (sp) and anal apodeme (aa); 50 = same, enlarged. seen in La, Pn or Dn, but slight asymmetrical variations in Tn: of five individuals studied, one lacked seta l’ from one trochanter IV, another lacked v’ from one genu I and one genu III, and another lacked it” from one tarsus III. Seta d of genua II and III minute (2–3 µm), blunt, subspiniform in La, despite not being coupled to respective solenidia; both attaining adult shape and form in Pn. Seta d of genu I with similar change in form, but position also changes: one alveolar diameter distal to solenidion σ’ in La, but 2–3 diameters distal in nymphs. Leg IV of Pn with typical numerical setation (0–0–0–0–7), but single fastigial seta slightly on anterior, rather than posterior face; position maintained to adult with brightfield (51) or differential interference contrast; Fig. 53 insert layered. Figs 51–56. Eniochthonius spp. , adults. 51A = lateral aspect of E. mahunkai n. sp. (top, e = egg); 51B = E. minutissimus (bottom) from same sample at Cicero, New York; 52 = E. minutissimus , anterolateral aspect of bothridial seta ( bo ) and nearby region, specimen from Germany; 53 = E. crosbyi , dorsal aspect of bothridial seta, with insert showing dorsolateral aspect of famulus of E. crosbyi (A) and E. minutissimus (B), each ca. 10 µm; 54 = E. mahunkai sp. n. , ventral aspect of genital region (cf. Fig. 3; arrow points to oblique articulation between middle and anterior aggenital plates; 55 = E. crosbyi , same, but from dissected specimen; 56 = E. minutissimus , same (intact specimen from Poland). Scale bars: 100 µm (51), 10 µm (all others); ag = alveolus of aggenital seta; e = egg; pp = plicature plate. Fig. 52 SEM micrograph (from ALBERTI et al. 1994 ); others from light microscope (see Note 11). Solenidia on genua II and III and on tibia III less attenuated (ceratiform) in La, becoming attenuate (piliform) in Pn; other solenidia relatively unchanged through ontogeny. Immatures often have thinner branch of famulus not bract-like as in adult, but blunt and same length as knobbed branch ( Fig. 48 ). Gnathosoma . General structure as in adult except as noted. Subcapitulum with labiogenal groove slightly less conspicuous (see Note 12, Fig. 47 ). Adoral seta or 3 formed in Pn; genal seta m 2 formed in Dn. Palp femoral seta v” (inf ) formed in Dn, tarsal seta cmp formed in Pn. Etymology . This species is named in honor of Dr. Sándor MAHUNKA (Hungarian Natural History Museum, Budapest), who has studied the systematics of acariform mites for more than four decades. Simply put, his explorations of the global diversity of oribatid mites are unmatched and invaluable. Material examined . Holotype : USA ; New York ; Onondaga Co. , Baldwinsville ; Beaver Lake Nature Center , 43°10.69’N , 76°24.29’W , col. R .A. NORTON , 5-X-2005 , ex: sphagnum moss on side of hummocks in lakeside fen . Paratypes : 130 adults with same data as holotype . Holotype and 10 paratypes deposited in the collection of the Division of Insects , Field Museum ( FM ), Chicago , Illinois . Other paratypes deposited as follows: 10 in the Hungarian Natural History Museum , Budapest ; 10 in the Acarology Laboratory , The Ohio State University , Columbus , Ohio ; 14 in the Canadian National Collection , Ottawa ; and 86 in the collection of R . A. NORTON . All paratypes in alcohol except for several on slides in the latter two collections . Other records. USA. New York. Onondaga Co., Cicero Game Management Area ( 43°08.87’ N , 76°02.87’W ), 3-V-2005 , R. A. NORTON col., ex: Sphagnum and Polytrichum moss on sides of hummocks in blueberry bog. Wisconsin . Kenosha Co., Salem (W), Van Halter Bog, 15-VIII-1972 , W. Suter, col., ex: sphagnum moss. Canada . New Brunswick . Kent Co., Kouchibouguac National Park, 16-VI–1978 , E. Rickey, col., ex: sphagnum and rhododendron litter. Nova Scotia . Cape Breton Highlands National Park, North Mt. spruce forest and bog, 8-IX–1983 , V. BEHAN-PELLETIER , col., ex: Sarracenia , Sphagnum and dwarf larch litter. All known sites inhabited by E. mahunkai sp. n. are peatlands (fens or bogs), with sphagnum moss being a consistent component of the microhabitat. It is also consistently collected with E. minutissimus , although the microhabitat preferences of these species may differ. Based on unstructured sampling at the type locality and in a blueberry bog (technically a fen) at Cicero, New York , E. mahunkai is a dominant mite species in sphagnum moss on hummocks, while E. minutissimus is relatively infrequent. By contrast, in adjacent clumps of Polytrichum moss at each location E. mahunkai is much less abundant, about as frequent as E. minutissimus . In forest litter and humus about 100 m from the type locality E. mahunkai does not occur, but E. minutissimus is common.