Caleremaeus retractus ( Banks, 1947 )

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 : 406-417

Caleremaeus retractus ( Banks, 1947)

Carabodoides retracta Banks, 1947 ; p. 123. [Nomen nudum in Pearse 1946, p. 148] Caleremaeus retractus ( Banks, 1947) ; Marshall et al. 1987, p. 225

Etymology — Banks (1947) presented no explanation of the species epithet, and there are no hints in his description. Marshall et al. (1987) treated ‘retracta’ as an adjective and emended the name accordingly.

Type locality — The type specimens (below) derived from a study of soil animals of the Duke Forest (Durham Co., North Carolina) by Pearse (1946). The Duke Forest is somewhat fragmented and, since four different locations and habitats were studied, the exact origin of the types is unknown.

Type material — Banks (1947) reported two specimens in the type series. The holotype (original designation as ‘type’) is a slide-mounted specimen in the arachnid collection of the MCZ. The label bears the following data in Banks’ handwriting: ‘Duke Forest N. Car.; #475; Pearse; Carabodoides retracta Bks ; 3018 type.’ The mite is broken by crushing but has an estimated total length of about 320 µm. The second specimen is a paratype in the mite collection of the USNM. It is a gravid female, also broken, with an estimated original length of 340 µm and with the following label data in Banks’ handwriting: ‘Duke Forest, N.C. 238, Pearse, Jan. Carabodoides retracta Bks. Paratype.’ The measurements contrast significantly with the ‘.55 to.6 mm’ reported by Banks (1947).

Other material examined — Approximately 40 topotypic adults (24 females, 10 males, several undetermined) with the following data: North Carolina, Durham Co., Duke Forest (35° 58.9 ஥ N, 78° 56.6 ஥ W), 4-V-1979, L.J. Metz, col., from loblolly pine ( Pinus taeda Linn. ) and hardwood forest litter. Also available for study were 30 nymphs and more than 300 adults from a nearby location that we consider near-topotypes: North Carolina, Durham Co., G.W. Hill Demonstration Forest (36°12.1 ஥ N, 78°52.9 ஥ W), 1973 (various dates), L.J. Metz col., from loblolly pine forest litter and upper soil.

Diagnosis — Caleremaeus species with adults having total length 306–340 µm. Prodorsum with well-developed distal cusps. Each cusp longer than wide, pair usually close together and basally-connected; tip pointed, oblique beyond insertion of seta le. Lamella well defined proximally, with variable development more anteriorly; tutorium well developed, enantiophysis eA present. Usually with single small pair of dorsosejugal tubercles. Notogastral setae small (most 11–14 µm), inconspicuously barbed beyond basal cerotegument nodule. Epimeral groove 2 usually without bordering tubercles or knots; ventrosejugal groove with only enantiophysis eS. Female with five pairs of genital setae, male with 4–6. Leg femora each with porose area. Nymphs with bothridial seta elongate, nearly as long as prodorsum, squamose in distal half but without distinct head; gastronotic seta h 1 with length similar to that of bs, narrow, barbed throughout, pair closely parallel and distinctly bowed; exuvial scalps appearing reticulated in transmitted light.

Adult

Figures 1–5

Dimensions — Total length of 20 measured topotypes 306–340 µm (mean 324); maximum width 172–203 µm (mean 189). Female (n = 10) length 323–340 µm (mean 333), maximum width 191–203 µm (mean 198); male (n = 10) length 306–328 µm (mean 313), width 172–191 µm (mean 179).

Integument, setae — Cerotegument excrescences mostly in form of near-spherical nodule with short, thick stalk (like unopened ‘button’ mushroom). Nodules relatively uniform in size according to location: largest on mid-notogaster, 4–6 µm diameter ( Fig. 2A, C, D ), often well-spaced; slightly smaller (~ 3 µm) anteriorly and laterally on notogaster, densely packed, usually touching; smallest (~ 1–2 µm) on prodorsum, venter and legs; basal cerotegument layer on venter microgranular between nodules. Most dorsal setae (except bs) short, inconspicuous, acuminate; basal third hyaline, smooth, penetrating distinct, usually shaded, cerotegument nodule; distal region pigmented, with minute barbs on outer curvature (e.g. Figs 2G , 3D ). Most ventral setae simple, nearly straight, without pigment or distinct cerotegument nodule.

Prodorsum — Surface usually foveolate, with well-spaced circular depressions mostly 5–8 µm diameter ( Fig. 1A ), foveate in some ( Fig. 2G ); tip of rostrum and subtriangular posteromedial region (with muscle sigilla) mostly smooth. With basally-connected pair of strongly projecting cusps ( Fig. 2G ; cu), longer than wide, each bearing lamellar seta (le) near tip; lateral margin of cusp distal to le insertion sharply oblique, forming pointed tip directed anteromedially at variable, often asymmetrical angle; paired tips often pincer-like, separated by only 2–8 µm. Cusp pair usually appear connected basally, with U-shaped inner margin, separated by less than their length, rarely with wider separation ( Fig. 2H ). Submarginal crest (smc) extending beyond insertion of rostral seta (ro), completely around front of rostrum (Figs 1B, 2J, I, 3G); cuticle scrobiculate immediately below crest. Rostral bulge ( Fig. 2I, K, L ) conspicuous, with embossed pattern on ventral surface. Lamella well defined posteriorly (level of acetabulum I); with variable development more anteriorly, either extending onto base of cusps ( Fig. 2H ) or (more commonly) effacing proximal to cusps ( Figs 1A , 2G ). Tutorium effacing anteriorly, well developed posteriorly to form anterior part of prodorsal enantiophysis eA ( Fig. 1B ); posterior tubercle of e A well-defined, conical, nearly touching tutorium. Short longitudinal ridge present laterally, between seta ex and acetabula I, II ( Fig. 1B ). With single pair of small, rounded to subrectangular dorsosejugal tubercles, located at corners of smooth sigillar region ( Fig. 1A ; dt); tubercle sometimes doubled or bilobed ( Fig. 3 B–C). Bothridial seta (bs; ~ 55–60 µm) projecting dorsolaterally, slightly curved just outside bothridium, remainder straight; squamose head comprising half its length, lightly pigmented, usually with acute tip; stalk smooth, unpigmented ( Figs 1A , 2E ). Posterior wall of bothridium with strong, conical, tooth-like tubercle directed at humeral process of notogaster, and second more medial tubercle, usually smaller ( Figs 1A , 3 B–C). Seta le (~ 15 µm; Fig. 2G ) strongly curved medially, tips of pair overlapping or not according to form of cusps; ro (~ 15 µm) curved anteroventrally, inserting on submarginal crest at level slightly posterior to le; seta in (15–20 µm; Fig. 3G ) slightly curved or nearly straight, mutual distance 4–5 times length; seta ex (~ 15 µm) inserted between bothridium and short lateral ridge. Setal vestige exv ventral or posteroventral to ex, nearly touching its alveolus.

Notogaster — Length about 1.2 times width; usually evenly rounded posteriorly. Foveae mostly limited to transverse sulcus and to anterolateral region between setae c and la ( Fig. 3A ). Humeral process (hpr) medium-sized (8–10 µm long), tip usually not reaching bothridial tubercle across sejugal groove. Anterior margin (between hpr) irregular, with series of 4–12 small tubercles (up to 4 µm long), weak knots, or slight bulges ( Fig. 3 A-C). Most setae with form of prodorsal setae noted above, 11–14 µm; h 1 with same form, but usually slightly larger (12–18 µm), medially curled, mutual distance of pair about equal to length; p 2 – p 3 smaller (6–8 µm) and differently shaped, smooth, without pigment or basal cerotegument nodule ( Fig. 3D ). Lyrifissures ia, im, ip relatively large (10–14 µm; Fig. 3B ), ips, ih smaller (~ 6 µm).

Venter and lateral podosoma — Foveate in acetabular region and lateral parts of coxisternum ( Fig. 3F ), and usually in single transverse row behind smooth mentotectum; coxisternum without foveae centrally; with irregular muscle sigilla on inner face of cuticle. Laterosejugal enantiophysis (eL) with strong conical to rounded tubercles. Epimeral groove 2 usually smooth. Enantiophysis eS variable in size, tubercles overlapping or not reaching each other; without other tubercles or knots along ventrosejugal groove. With strong, sculpted discidial ridge (dir) posterior to acetabulum III and separate conical discidium dis () below it, near lateral end of epimeral border 3 ( Fig. 1B ). Lateral coaptive ridges well-formed, connecting posterior tubercle of eS, discidium, and (usually) anterior tubercle of e4 ( Fig. 3F ). Epimeral setae acuminate to attenuate (~ 12–15 µm). Aggenital enantiophysis (e4) strongly developed. Medial fossa of epimere IV often with small pair of projections on margin ( Fig. 3F ). Anogenital region relatively smooth, but with inconspicuous fine striation in adanal region ( Fig. 3E ). Apophysis of preanal organ slightly tapered to slightly expanded ( Fig. 3F, H, I ). Females consistently with five pairs of genital setae; males variable, 4–6 (of 18 male plates examined, nine with 4 setae, eight with 5, one with 6; asymmetrical in five of nine individuals). Anogenital setae acuminate; aggenitals and genitals ~ 6–7 µm, anals ~ 5–6 µm; adanals ~ 6–9 µm (ad 1 longest). Lyrifissure iad ~ 12 µm ( Fig. 3E ).

Gnathosoma — Subcapitulum smooth or with few scattered foveolae; hypostomal (h, ~ 14 µm) and genal (a, m, ~ 15–18 µm) setae attenuate. Chelicera ~ 80 µm long, with 0–2 small spicules; setae cha (~ 22 µm), chb (~ 15 µm) attenuate, barbed.

Legs ( Figs 4–5 ) — Femora I, II similar in form: with abrupt transition from proximal stalk to bulb, junction at nearly right-angle; femur I ~2.5, II ~2.0 times longer than high in lateral view, stalk occupying ~0.4 femoral length; stalk of femur II slightly broader than that of I. All femora with porose area, mostly on adaxial face of bulb. Tibia I with bulb markedly swollen, only ~1.2 times longer than high. Tarsus I abruptly tapered in distal half, but without distinct projecting mid-dorsal bulge. Tarsus II without noticeable proximal stalk, depth similar to that of tibia in lateral view. Seta d of femora short, flame-shaped, similar in structure to dorsal body setae (pigmented, barbed, with conspicuous cerotegument nodule at base; Fig. 5D ). Seta l ஥ of genu and tibia I not conspicuously enlarged.

Juveniles

Figures 6–7

(Larva known only from exuvial scalp)

Length (without setae) and maximum width of protonymph 230 x 98 µm (n = 1); deutonymph 230–289 x 107–142 µm (n = 9); tritonymph 284–353 x 147–181 µm (n = 7).

Bothridial seta ( Figs 6A , 7H ) straight, elongated, nearly as long as prodorsum, gradually thickening distally but without distinct head, slightly lanceolate with angular tip; distinctly squamose in distal half. Setae in, ex, le minute, hardly extending beyond basal cerotegument nodule; ro about twice as long but inconspicuous, curved ventrad. Seta le inserted on weak tubercle, slightly longer than wide; ro inserted on truncate rostral projection appearing like anterior part of submarginal crest of adult ( Figs 6B , 7F ). Gastronotic region of larva (based on exuvial scalp; Figs 6A , 7 B–C) with setae c 1, c 2, la, lm, lp minute (~ 3–4 µm), smooth, acicular to nearly baculiform, hardly emerging from basal cerotegument nodule; dorsocentral setae closely paired (mutual distance 10–13 µm), da (~ 8–9 µm) and dm (~ 11–12 µm) slightly arched, with strong barbs on outer curvature, dp (~ 24–26 µm) weakly clavate, strongly squamose; h 1 similar to dp but shorter (~ 15–17 µm). Setal pair h 1 closely parallel, greatly elongated, ~ 130–150 µm in tritonymph (length relative to body length ~ 0.3 in proto-, 0.4–0.5 in deuto-, tritonymph); uniformly narrow except slightly tapered distally, with small but conspicuous barbs throughout. Nymphal seta p 1 subclavate seen face-on but slightly flattened and cupped, strongly squamose on upper curvature (~ 20 µm in tritonymph); other gastronotic setae minute, simple, (4–8 µm in tritonymph), hardly emerging from basal cerotegument nodule ( Fig. 7 I–K). Ventral setae simple, acuminate, without cerotegument nodule; in tritonymph, epimeral setae 6–9 µm, genital and aggenital setae ~ 4 µm, ad setae 6–7 µm, an 4–5 µm. Genital seta ontogeny variable: deutonymph with two or three pairs, tritonymph with four or five, valves sometimes with asymmetrical complement. Lateral setae of legs generally short, inconspicuous; l ′ of tibia I hardly reaching distally to end of segment ( Fig. 7M ); seta d of tibia I with cilia and velumlike coating indistinct ( Fig. 7L ). Exuvial scalps conspicuously reticulated due to fovea-like excavations on underside ( Fig. 6 A–B, 7A–C, E); seta h 1 consistently broken from nymphal exuviae.

Comparisons

Adults of Caleremaeus retractus are similar to those of C. monilipes (cf. Weigmann 2006, Miko and Travé 1996) and C. divisus in having a distinct lamella and tutorium and lamellar seta inserted on a strong cusp, traits that are absent from C. arboricolus and C. nasutus . According to the crude illustration of C. divisus , the cusp stops well short of the rostral margin, while reaching or surpassing it in C. monilipes and C. retractus ; also, the anterior notogastral tubercles of C. divisus were drawn as far larger than those of other species, equal in size to the humeral process ( Mihelčič 1952).

Adults of Caleremaeus retractus are distinguishable from those of C. monilipes (Cm) by: (1) having a less sculptured prodorsum, including weakly-developed lamella (stronger in Cm); (2) having nearly erect setae in, the pair separated by 4–5 times setal length (in slightly larger, curved mediad and separated by less than three times setal length in Cm); (3) lacking additional distinct knots or small tubercles along epimeral groove 2 and along the anterior edge of the sejugal groove between tubercle pair Sa (present in Cm); (4) having a modest humeral process that rarely reaches anteriorly to overlap bothridial tubercles (larger humeral process, overlapping with bothridial tubercle in Cm); (5) being smaller, with adult total length 306–340 µm (373–475 µm in Cm). Nymphs are distinguishable by: (1) the narrow, elongate form and closely parallel orientation of setae h 1 in nymphs (distinctly clavate and divergent in Cm; Fig. 18C ); (2) having generally smaller, less conspicuous leg setae (generally larger in Cm; cf. setae l ஥ in Figs 7M , 18D ); having smooth, small, inconspicuous seta ro (larger, conspicuous, with several strong barbs, projecting distinctly forward beyond rostral margin in Cm; Fig. 18D , see also Michael 1882).

Possible species group

As noted in the Introduction, morphometric and genetic evidence suggests that European records of Caleremaeus monilipes represent a complex of species ( Krisper et al. 2017) that ultimately may be considered the ‘monilipes’ species-group. The same may be true of the most similar North American species, C. retractus .

At an early stage of this study, we identified specimens of C. retractus from many locations in eastern North America, including the states of Alabama, Arkansas, Florida, Georgia, Louisiana, Illinois, Indiana, Mississippi, New Hampshire, New York, Vermont, Virginia and West Virginia, as well as the Canadian province of Quebec. Adults of these specimens are presently indistinguishable from those at the type location in North Carolina, except perhaps for a propensity of New York adults to have one or two small knots across epimeral groove 2 from seta 2a ( Fig. 18E ). But juveniles suggest that more than one species is involved. In addition to the near-topotypical material from Durham Co., North Carolina, we have juveniles from Florida and from New York (Onondaga Co.). The Florida nymphs are identical to the near-topotypes, but New York juveniles are easily distinguished by their shorter, straighter pygidial setae ( Fig. 18G; h ), larger seta l ஥ on tibia and genu I, and tibia I seta d with more distinct barbs and 1 velum-like coating. As with near-topotypes, setae h 1 of the New York population are adjacent, parallel and consistently broken from exuviae, unlike those of C. monilipes and C. arboricolus in which they are divergent and retained on exuviae.

The differences could represent geographic variation in these setae, but without further knowledge of juveniles from other locations, and especially without genetic data, we have no basis for judgement. At present, we prefer to assign specimens with the adult traits of C. retractus to a ‘retractus’ species group unless juveniles are known and correspond with the near-topotypes.

Figures

Figure 1 Caleremaeus retractus(Banks), adult: A – dorsal view (legs mostly omitted); B – lateral view (gnathosoma, legs and anal, genital plates omitted); C – subcapitulum, ventral view (adoral lips and palps omitted); D – palp, abaxial view. Scale bars: 50 µm (A, B); 10 µm (C, D).

Figure 2 Caleremaeus retractus(Banks), transmitted-light micrographs of near-topotypical adults: A – dorsolateral view; B – posterior view; C – cerotegument separated from notogaster, lateral view; D – same, dorsal view (face-on); E – bothridium and bothridial seta (head face-on); F – optical sections of bothridium; upper image focused fine circular striations of inner chamber, lower image on longitudinal striations of deepest part of inner chamber; G – anterior region of prodorsum, dorsal view (insert = enlargement of seta le, arrow to break in seta emphasizing surrounding cerotegument nodule); H – same, different specimen, showing cusp variation; I – anterior region of specimen in G, deeper focus showing rostral bulge and submarginal crest; J – prodorsum, dorsolateral view (gnathosoma removed; setaele and ro represented only by birefringent core); K – specimen in J, deeper focus on rostral bulge (arrowhead to transverse striae of embossed pattern on inner surface of rostral bulge; L – rostral region of dissected specimen, anterior view (black arrow to central ridge of embossed pattern on inner face of rostral bulge); M – parasagittal section of prodorsum and anterior hysterosoma (insert = enlarged base of rostral bulge and rostrophragma). Scale bars: 50 µm (A, B); 20 µm (J, M); 10 µm (E, G-I, K, L); 5 µm (C, D, F).

Figure 3 Caleremaeus retractus(Banks), transmitted-light micrographs of near-topotypical adults: A – anterior region of separated notogaster; B – right sejugal region, dorsal view; C – same, different specimen; D – notogastral setae, as labeled; E – adanal region and anal plate (no setae in focus); F – partial venter (setae seen only as alveolus due to focus limitations); G – rostrum and subcapitulum, ventral view; H – preanal organ and associated muscles (no clearing); I – two variants of same, with strong clearing; J – sagittal section of posterior hysterosoma. Scale bars: 20 µm (F); 10 µm (A-C, E, G, J); 5 µm (H, I); 2 µm (D).

Figure 4 Caleremaeus retractus(Banks), legs of adult (abaxial aspect, trochanter omitted from I, II): A – leg I; B – leg II; C – leg IV. Scale bar: 20 µm.

Figure 5 Caleremaeus retractus(Banks), transmitted-light micrographs of near-topotypical adults: A – legs I-IV, abaxial view (trochanters I, II not shown); B – trochanter and base of femur IV, mid-depth focus; C – same, deeper focus; D – partial leg III, with enlarged femoral seta d (upper left insert, arrow to basal cerotegument nodule) and tibial solenidionφ (upper right insert); E – left gena and rutellum, ventral view (removed from subcapitulum); F – chelicera, adaxial view; G – egg removed from oviduct. Scale bars: 20 µm (A, G); 10 µm (B-D, F); 5 µm (E).

Figure 6 Caleremaeus retractus(Banks), juveniles: A – protonymph, dorsal view; B – deutonymph, lateral view, with smaller setae omitted from larval (SLa)and protonymphal (SPn) scalps. Dots indicate that seta is on exuvial scalp (one for larval, two for protonymphal). Scale bars: 50 µm (B); 10 µm (A).

Figure 7 Caleremaeus retractus(Banks), transmitted-light micrographs of near-topotypical juveniles: A – protonymph, dorsal view (setae h1 incomplete); B – same, lateral view of posterior hysterosoma; C – deutonymph, lateral view of hysterosoma; D – tritonymph, dorsal view (insert = right lamellar seta and cusp); E – same, lateral view of hysterosoma; F – tritonymph, ventral view of prodorsal margin and partial gnathosoma (upper right insert = enlarged seta ro); G – gastronotic cornicle of tritonymph (scalps removed); H – bothridial seta of deutonymph; I – gastronotal seta lm from tritonymph (arrow to basal cerotegument nodule); J – same, but seta h2; K – same, but setap2; L – dorsodistal process of tibia I, tritonymph, distal to left (φ1 rising out of focus; insert = opposite side of seta d, showing faint barbs); M – tibia, genu and distal part of femur I from tritonymph, adaxial view; N – coupled seta d and solenidion on tibia II (distal to left). Dots in B, C, E indicate that labeled seta (or its insertion) is on exuvial scalp of larva (.), protonymph (..) or deutonymph (…). Scale bars: 50 µm (D); 20 µm (A-C, E); 10 µm (M); 5 µm (F-H, L, N); 2 µm (I-K).

Figure 18 Transmitted-light micrographs of C. monilipes,(A-D) and Caleremaeus‘retractus’ group from New York (E-G): A – adult (from Sweden), rostral bulge, deep focus to show embossed pattern; B – adult (from Spain), setah2 and nearby cerotegument; C – deutonymph (from Sweden), pygidial region, ventral view of flattened specimen; D – same, leg I and rostral region, dorsal view (lower left insert: tibia II coupled seta d and solenidion); E – anterior part of coxisternum; F – anterior third, ventrolateral view; G – deutonymph, hysterosoma, lateral view. Scale bars: 20 µm (C-G); 10 µm (A, B).