Pseudocheylus americanus (Ewing, 1909)

Skvarla, Michael J., Fisher, J. Ray & Dowling, Ashley P. G., 2013, On some mites (Acari: Prostigmata) from the Interior Highlands: descriptions of the male, immature stages, and female reproductive system of Pseudocheylus americanus (Ewing, 1909) and some new state records for Arkansas, Zootaxa 3641 (4), pp. 401-419 : 402-415

Pseudocheylus americanus (Ewing, 1909)

( Figs. 1–9 )

Cheyletiella americana Ewing 1909: 429 , fig. 15.

Pseudocheylus americanus (Ewing) Baker & Wharton 1952: 226 ; Baker 1958: 136; Baker & Atyeo 1964: 259, figs. 6–8; Van Dis & Ueckermann 1991: 105.

Diagnosis. Pseudocheylus americanus can be differentiated from P. biscutatus (Berlese, 1888) , the only other Pseudocheylus , by the lack of tarsal claws on leg I.

Imago description. Females and males similar, except for genital and chaetotaxic differences noted below. In life, integument clear to slightly opaque white, with red internal coloration in body that extends into basal leg segments (fig. 1). Most setae slightly to densely barbulate (for example, see fig. 9), though they have been illustrated as smooth to retain clarity in figures.

Female (n=5). 720–1080 (914) long, 420–770 (574) wide.

Gnathosoma. Subcapitulum less than half the length of the idiosoma, 248–303 (265). Two pairs of adoral setae and two pairs of subcapitular setae present. Palp 213–288 (246) long, 88–110 (97) wide. Setal count: trochanter—0; femur—14; genua—2; tibiae—3, 2 spine-like setae, 1 claw-like setae; tarsus—7. Chelicera 240– 250 (244) long, 70–88 (77) wide, tapering anteriorly. Two setae present, one at apex and one on anterior half.

Dorsum (fig. 2). Two pairs of eyes present; anterior pair with lenses, posterior pair without lenses or other external marks (see remarks). Proterosomal shield present, unsclerotized; differentiated by weaker, self enclosing striations. One pair of setose trichobothria, 65–78 (73) long, and 15–16 pairs of setae present. Hysterosoma with approximately 50 pairs of setae; setal rows difficult to differentiate. Two anal setae present dorsally. Integument striated.

Venter. Coxal plates I and II closely approximated; coxal plates III and IV also closely approximated, fused toward midline. Coxae I–IV setal formula 3-3-3-2. Three genital setae present ( Figs. 7 f, 8). 65–70 pairs of setae present, including 4 pairs of apparently pseudanal setae.

Legs. Leg I longer than body, legs II–IV shorter than body. Leg I 950–1110 (1028), leg II 300–600 (494), leg III 530–690 (616), leg IV 610–790 (730). Setal formula: trochanters I–IV, 2-1-2-1; basifemora I–IV, 23-17-12-8 to 11; telofemora I–IV, 6-3-4-3; genua I–IV, 17-8-7 to 9 -7 to 8; tibiae I–IV, 15 to 17 -10-14-15 to 16; tarsi I–IV, 30 (1)- 17 (1)-35 to 38-44 to 46.

Male (n=3). Same as female, except as follows. 780–950 (870) long, 410–590 (517) wide.

Gnathosoma. Subcapitulum 225. Palp 200–213 (208) long, 83–98 (88) wide. Chelicera 200–213 (206) long, 65–70 (67) wide.

Venter. Eight genital and 7–10 paragenital setae present. Large, internal genital structure ( Fig. 7 e) visible through integument.

Legs. Leg I 890–1050 (953), leg II 400–450 (423), leg III 500–590 (550), leg IV 580–680 (637). Setal formula: basifemora I–IV, 27-17 to 18-12 -9 to 10; telofemora I–IV, 6 to 7-3-4-4; genua I–IV, 17-9-8-9 to 10; tibia I–IV, 17- 10-13 to 14-14; tarsi I–IV, 32 (1)-17 (1)-46 to 48-44 to 48.

Immatures description. Immature Pseudocheylus americanus superficially resemble adults. They can be differentiated by the number of legs (larvae have six legs), generally smaller size, genital development, and chaetotaxy. Most setae are slightly to densely barbulate.

Tritonymph (n=2). 650–780 (715) long, 450–550 (500) wide.

Gnathosoma. Subcapitulum less than half the length of the idiosoma, 163–175 (169). Two pairs of adoral setae and two pairs of subcapitular setae present. Palp 163–200 (181 long, 70–75 (73) wide. Setal count: trochanter—0; femur—11; genua—2; tibiae—3, 2 spine-like setae, 1 claw-like setae; tarsus—7. Chelicera 163– 178 (170) long, 58–63 (60) wide, tapering anteriorly. Two setae present, one at apex and one on anterior half.

Dorsum (fig. 3). Proterosomal shield present, unsclerotized; differentiated by weaker, self enclosing striations. One pair of setose trichobothria, 55–68 (61) long, and 7–9 pairs of setae present. Hysterosoma with 26–29 pairs of setae. Two anal setae present dorsally. Integument striated.

Venter. Coxal plates I and II closely approximated; coxal plates III and IV also closely approximated, fused toward midline. Coxae I–IV setal formula 3-3-3-1. Three genital setae present (fig. 7d). 32–36 pairs of setae present, including 2 pairs of apparently pseudanal setae.

Legs. Leg I longer than body, legs II–IV shorter than body. Leg I 640–680 (660), leg II 330–350 (340), leg III 450–540 (495), leg IV 450–500 (475). Setal formula: trochanters I–IV, 1-1-2-1; basifemora I–IV, 21-13-9-6; telofemora I–IV, 6-3-3-3; genua I–IV, 12-6-6-3; tibiae I–IV, 12-5-10-10; tarsi I–IV, 25 to 27 (1)-13 (1)-25-24 to 25.

Deutonymph (n=4) 470–630 (558) long, 290–400 (336) wide.

Gnathosoma. Subcapitulum less than ½ the length of the idiosoma, 100–155 (131). Two pairs of adoral setae and two pairs of subcapitular setae present. Palp 125–163 (148) long, 55–68 (62) wide. Setal count: trochanter— 0; femur—5; genua—2; tibiae—3, 2 spine-like setae, 1 claw-like setae; tarsus—7. Chelicera 128–145 (138) long, 45–63 (54) wide, tapering anteriorly. Two setae present, one at apex and one on anterior half.

Dorsum. (fig. 4). Proterosomal shield present, unsclerotized; differentiated by weaker, self enclosing striations. One pair of setose trichobothria, 53–68 (62) long, and 6 pairs of setae present. Hysterosoma with 18 pairs of setae. Two anal setae present dorsally. Integument striated.

Venter. Coxal plates I and II closely approximated; coxal plates III and IV also closely approximated, fused toward midline. Coxae I–IV setal formula 3-3-3-0. Genital setae absent (fig. 7c). Fourteen pairs of setae present, including 2 pairs of apparently pseudanal setae.

Legs. Leg I longer than body, legs I–IV shorter than body. Leg I 490–620 (534), leg II 248–413 (324), leg III 310–430(384), leg IV 360–430 (402). Setal formula: trochanters I–IV, 1-1-2-1; basifemora I–IV, 10-6-5-1; telofemora I–IV, 6-3 to 4-3-3; genua I–IV, 8-4-4-4; tibiae I–IV, 6-5-5-5; tarsi I–IV, 22 (1)-9 (1)-14-12.

Protonymph (n=1) 510 long, 313 wide.

Gnathosoma. Subcapitulum less than ½ the length of the idiosoma, 128. Two pairs of adoral setae and two pairs of subcapitular setae present. Palp 123 long, 50 wide. Setal count: trochanter—0; femur—2; genua—1; tibiae—3, 2 spine-like setae, 1 claw-like setae; tarsus—7. Chelicera 113 long, 50 wide, tapering anteriorly. Two setae present, one at apex and one on anterior half.

Dorsum (fig. 5). Proterosomal shield present, unsclerotized; differentiated by weaker, self enclosing striations. One pair of setose trichobothria, 58 long, and 4 pairs of setae present. Hysterosoma with 9 pairs of setae. Two anal setae present dorsally. Integument striated.

Venter. Coxal plates I and II closely approximated; coxal plates III and IV also closely approximated, fused toward midline. Coxae I–IV setal formula 3-3-1-0. Genital setae absent (fig. 7b). Twelve pairs of setae present, including 1 pair of apparently pseudanal setae.

Legs. Leg I longer than body, legs II–IV shorter than body; femora IV completely fused. Leg I 400, leg II 233, leg III 350, leg IV 333. Setal formula: trochanters I–IV, 1-1-2-0; basifemora I–III, 3 to 4-5-0; telofemora I–III, 4-4- 3; femora IV, 0; genua I–IV, 5-4-4-1; tibiae I–IV, 5-5-5-1; tarsi I–IV, 21 (1)-9 (1)-13-8.

Larva (n=1) 390 long, 250 wide.

Gnathosoma. Subcapitulum less than 1/3 the length of the idiosoma, 110. Two pairs of adoral setae and two pairs of subcapitular setae present. Palp 100 long, 48 wide. Setal count: trochanter—0; femur—2; genua—1; tibiae—3, 2 spine-like setae, 1 claw-like setae; tarsus—6. Chelicera 95 long, 40 wide, tapering anteriorly. Two setae present, one at apex and one on anterior half.

Dorsum (fig. 6). Proterosomal shield present, unsclerotized; differentiated by weaker, self enclosing striations. One pair of setose trichobothria, 53 long, and 3 pairs of setae present. Hysterosoma with 6 pairs of setae. Two anal setae present dorsally. Integument striated.

Venter. Coxal plates I and II closely approximated. Coxae I–III setal formula 2-1-1. Genital setae absent (fig. 7a). Two pairs of setae present.

Legs. Leg I longer than body, legs II and III shorter than body. Femora I–III completely fused. Leg I 310, leg II 178, leg III 220,. Setal formula: trochanters I–III, 1-0-1; femora I-III, 5-4-3; genua I–III, 4-4-4; tibiae I–II, 5-5-5; tarsi I–III, 11 (1)-9 (1)-9.

Remarks. Ewing (1909) provided a small illustration of the dorsal habitus of the adult female which, while useful for gestalt, lacks the detail to be used diagnostically. He stated that the species has “on each side of the base of the mandibles and not far from the same is a prominent, curved horn about as long as the width of the mandibles” and the “mandibles each [have] three bristles; a long, straight bristle at about one-third the distance from the anterior end, a similar bristle at about the middle of the mandibles, and a much shorter one situated just about the piercing organ”.

Baker (1958) presented detailed drawings of the dorsal habitus, tibiae I and tarsi I, the tip of tarsi I, and the dorsal gnathosoma of a mite only identified as “ Pseudocheylidae ”. These illustrations were reproduced by Baker and Atyeo (1964), who reported them to be drawings of Pseudocheylus americanus . In these drawings the peritremes are depicted as terminating on the gnathosoma and not looping back towards the body. The horns described by Ewing are lacking. Baker and Atyeo also depicted two setae on the chelicerae instead of the three described by Ewing. Vin Dis and Ueckermann (1991) wrote that Baker and Atyeo (1964) reported the shape of the peritreme can be used to differentiate P. americanus and P. biscalatus , the only other described species. The authors could not find such a direct statement, however Baker and Atyeo (1964) state that “Berlese (1888) [referring to P. biscalatus ] defined the genus, in part, as having peritremes appearing as little horns…The genus must be redefined to include species with distally free peritremes.” This suggests they considered P. americanus to have distally free peritremes.

To resolve these issues the authors wished to view the type material. Ewing did not say where he deposited the two slides of P. americanus he examined, however Baker and Atyeo (1964) reported them to be in the United States National Museum collection. A search was made by Debra Creel but the slides were not found. Dr. Barry OConnor was kind enough to examine the slide material Dr. Atyeo donated to the University of Michigan, but the types were not present there either. We suggest the types are probably lost.

When the freshly collected specimens reported here were examined under low power, the peritremes, which form a loop that is free of the body, look like the “horn” Ewing illustrated and Berlese used to define the genus. We therefore suggest that our specimens are P. americanus and that either the illustrations by Baker (1958) and Baker and Atyeo (1964) depict another genus of Pseudocheylidae or do not accurately depict the peritremes of P. americanus .

The chelicerae of the newly collected specimens possess two setae, one distally near the movable digit and one approximately one-third the distance from the tip. There is, however, a pair of setae on the subcapitulum that might appear to be on the chelicerae if the chelicerae are not forced into an unnatural position during mounting. We suggest this is the third seta reported by Ewing that was subsequently not included in the illustration by Baker and Atyeo.

Two pairs of eyes are readily apparent in unmounted specimens (see for example fig. 1). The anterior pair is designated by having a lens, while the posterior pair lacks such a lens. When cleared or slide mounted in Hoyer’s medium the posterior pair of eyes are obliterated and no external indication of them on the cuticle is present. Ewing (1909) and subsequent authors do not mention this second pair of eyes, possibly because they only examined slide mounted specimens in which the eyes would not be apparent.

The trichobothria in Anystoidea have historically been considered to be homologous to setae sci of other mites (Kethley 1990; Krantz & Walter 2009). In Pseudocheylus americanus the trichobothria of the larvae are posterior to a second pair of internal setae. Two hypotheses might account for this: the trichobothria are setae vi and not homologous to the trichobothria of other Anystoidea or the trichobothria are sci and have migrated anteriorly while vi have migrated posteriorly. The authors have labeled the figures as per historical conventions (e.g., the trichobothria are sci), though this needs further study.

The palp tibiae and tarsi have historically been illustrated as being completely fused without any indication of the suture lines (see for example Van Dis & Ueckermann 1991). Upon close examination it is possible to discern the outline of the tarsi and therefore assign setal counts to the individual segments (fig. 9).

Stephen and Kinn (1980) collected two unidentified Pseudocheylus specimens near Ashdown, Arkansas on Dendroctonus frontalis ( Curculionidae : Scolytinae ), upon which they were apparently phoretic. While P. americanus is the only Pseudocheylus known from North America, the authors cannot confirm the identity of the specimens as the slides have apparently been lost. These new specimens therefore represent the first record of Pseudocheylus americanus from Arkansas.

Material examined. 5 females, 3 males, 1 tritonymph, 4 deutonymphs, 1 protonymph, 1 larva (APGD 11- 0712-001) (all slide mounted), under bark of dead tree, USA, Arkansas, Washington Co., Fayetteville, Lake Sequoia, 12 July 2011, coll. A. Lynn-Miller.

Caeculidae

Caeculus cremnicolus Enns, 1958

Caeculus cremnicolus Enns 1958: 107 , figs. 1–6;Dunn 1976: 2, figs. 1, 2; Hagan 1985: 245; McDaniel & Boe 1990: 723.

Diagnosis. Caeculus cremnicolus is differentiated from other North American Caeculus by the median dorsal hysterosomal plate possessing more than 3 pairs of setae, the propodosomal plate projecting anteriorly over the gnathosoma, and opisthosomal transverse plates I and II not fused along midline, instead forming two pairs of small oval plates.

Remarks. This species has previously only been documented from the type location in Boone Co., Missouri. Dunn (1976) used C. cremnicolus as a model organism in cluster and principal component analyses, but obtained the specimens from Dr. W. R. Enns and did not report the location they were collected. These new specimens increase the range of the species by approximately 400 km and suggest it may be found throughout the Interior Highlands.

Material examined. 1 larva (APGD 08-0509-003), ex litter, USA, Arkansas, Buffalo National River, Steel Creek (36°01’55.2”N, 93°20’02.4”W), 9 May 2008, coll. A. P. G. Dowling ● 1 individual (APGD 10-0730-004), ex semidry mixed cedar and deciduous litter, same locality (36°01.924’N, 93°20.040’W), 30 July 2010, coll. M. J. Skvarla ● 2 individuals (APGD 10-0730-006), ex moist litter drifts against hillside in creek bottom, same locality (36°02.213’N, 93°20.137’W), 30 July 2010, coll. M. J. Skvarla ● 1 individual (APGD 10-0314-013), ex litter, USA, Arkansas, Newton Co, Buffalo National River, Boen Gulf (35°52.010’N, 93°24.060’W), 14 March 2010, coll. M. J. Skvarla ● 1 individual (APGD 10-0314-017), same habitat and locality (35°52.040’N, 93°24.081’W), 14 March 2010, coll. M. J. Skvarla ● 1 individual (APGD 10-0417-001), same habitat and locality (35°51.992’N, 93°24.046’W), 17 April 2010, coll. M. J. Skvarla ● 1 individual (APGD 10-0518-017), same habitat and locality (35°52.010’N, 93°24.060’W), 18 May 2010, coll. M. J. Skvarla ● 1 individual (APGD 10-0919-003), ex mixed cedar and deciduous litter in deep crevice between rocks, same locality (36° 02.381 N, 93° 20.394 W), coll. M. J. Skvarla ● 1 individual (APGD 10-0919-006), ex mixed cedar and deciduous litter in drifts against logs and rocks, same locality, 19 Sept. 2010, coll. M. J. Skvarla ● 2 individuals (APGD 10-0919-007), same habitat and locality, 19 Sept 2010, coll. M. J. Skvarla ● 4 individuals (JRF 12-1029-002), ex leaf litter, USA, Arkansas, Conway Co., Petit Jean State Park (35°6’58”N, 92°56’31”W), 28 October 2012, coll. J. R. Fisher.

Figures

FIGURE 1. Pseudocheylus americanus (Ewing, 1909). Stereomicrographs of specimens in ethanol.

FIGURE 7. Pseudocheylus americanus (Ewing, 1909). Anogenital developmental sequence. Internal structures represented by dotted lines. a — larva. b — protonymph. c — deutonymph. d — tritonymph. e — adult female. f — adult male.