Podotarsonemus Seeman, Lindquist & Husband, 2018

Seeman, Owen D., Lindquist, Evert E. & Husband, Robert W., 2018, A new tribe of tarsonemid mites (Trombidiformes: Heterostigmatina) parasitic on tetrigid grasshoppers (Orthoptera), Zootaxa 4418 (1), pp. 1-54 : 7-10

Podotarsonemus Seeman, Lindquist & Husband gen. nov.

Type species: Podotarsonemus boliviensis Seeman, Lindquist & Husband sp. nov.

Diagnosis. With attributes of tribe Podotarsonemini, augmented as follows: Palpi much reduced, without clear segmentation; apical palpal seta flanked medially by small hyaline triangular flange. Cheliceral stylets of larvae and adults curved from base to apex, with 0–2 teeth subapically. Adults and larvae with scapular setae sc2 at most slightly longer than interval between their insertions, not exceedingly long, attenuated. Adult female prodorsal stigmata with main tracheal trunks leading internally to atrial chamber(s) and then to distinctively enlarged pair of post-atrial structures. Legs II–III of larvae and adults often lacking all genual setae (v″ always absent), and leg III lacking femoral setae. Larvae with setae on coxisternal plates III well developed, often attenuated, and with setae ps well-developed, sometimes attenuated, along with setae h. Male leg IV without flanges, femorogenu IV with maximum of one seta Ge- vʹ. In contrast to Acarapis , leg IV is slender in addition to characters already described for the tribe.

Description. Gnathosoma . Form and structures of gnathosoma similar on larva, female, and male, though generally slightly larger on female. Capsule broadly oval in dorsoventral view, not beak-like anteriorly; palpcoxal setae present on adults. Dorsal gnathosomatic setae variably long, slender, smooth on adults, similarly formed on larva. Palpi directed anteriorly, short, stubby, with short but prominent, stout, pointed genual seta projected anteriorly and sometimes a smaller, inconspicuous femoral seta posterolaterally, these flanked anteroventrally by small, bluntly pointed, apical hyaline flange-like margin of femorogenual segment which covers rudimentary tibiotarsus with its terminal ventro-apical zone of alveolar vestiges of 3–5 small circular structures, probably rudiments of setae, solenidia and claw elements. Cheliceral stylets prominent, thick, variably protruding from capsule, smooth or with 1–2 teeth subapically, curved laterally in attachment to large basal levers oriented transversely across anterior one-third of capsule. Pharynx striated, muscular, with thinly sclerotized walls, enlarged to about one-third the width of gnathosomatic capsule, with paired gland-like structures indiscernible posteriorly.

Idiosoma . ADULT FEMALE. Dorsal shielding unornamented or reticulated, imbricated. Dorsal setae collectively smooth or with small barbs on setae c1, d, e, f. Prodorsal shield not extended hood-like over gnathosoma . Stigmata opening closely anterolaterad setae v1; main tracheal trunks with enlarged, slightly sclerotized atrial sacs (sometimes fused into single sac), and also with slightly to heavily sclerotized post-atrial sacs, these entire (much as in Hemitarsonemus ). Pits v2 obliquely aligned with setae v1 and sc2, and situated about one-quarter to midway along interval from v1 to sc2, sometimes at anterolateral invaginations of prodorsal shield. Setae sc2 long, attenuate, more widely spaced from each other, and longer, than v1, but not exceedingly long, at most slightly longer than transverse interval between their insertions, and inserted near midlength of prodorsal shield. Bothridia vestigial or absent, their sensilla sc1 reduced, slender, or absent. Tergite EF with setae e and f transversely aligned, similar in length, not grouped closely together. Tergite H with setae h short to exceedingly long, attenuate.

Ventral shielding with apodemes 1 forming Y-shaped juncture with prosternal apodeme. Apodemes 2 fully or weakly connecting with prosternal apodeme. Prosternal apodeme developed posteriad level of apodemes 2 but not reaching posterior margin of coxisternal plates II. Sejugal apodeme reduced to a lateral fragment on either side. Apodemes 3 not extending laterad trochanters III, nor mediad setae 3a. Apodemes 4 reduced medially and not connected to each other, but extending posterolaterad setae 3b to base of trochanters IV. Poststernal apodeme absent. Coxisternal plates I and II with setae 1a and 2a short to exceedingly long, attenuated, similar in size. Anterior margin of coxisternal plates III straight or convex, if convex then sometimes extending over posterior edge of coxisternal plates II. Coxisternal setae 3a and 3b short to exceedingly long, attenuated, similar in size. Bases of legs IV well spaced, separated by interval of three to four widths of trochanter IV; posterior margin of coxisternal plates IV weakly formed, not formed into tegular projection. Pseudanal setae ps exceedingly long, attenuate.

ADULT MALE. Dorsal shielding unornamented. Dorsal setae collectively smooth, much as in female, but if attenuated, then less extremely so. Prodorsum with three pairs of setae, including short but well developed sc1; setae sc2 attenuate but not exceedingly long, no longer than transverse interval between their insertions; setae v2 lacking but vestiges of their alveoli indicated by a pair of pits. Plate CD with setae arranged in two or three transverse rows, pair c2 anteriorly, d posteriorly, and c1 either at same level between c2 or at level between (and often obliquely aligned with) c2 and d. Plate EF with setae e and f more or less aligned transversely. Genital capsule with adhesive copulatory flanges reduced or absent.

Sejugal apodeme evident laterally but indistinct medially. Coxisternal plates III and IV partly or entirely separated from each other medially by soft cuticle, such that apodemes 3 and 4 not reaching each other medially and poststernal apodeme absent; apodemes 5 moderately to weakly formed on either side at bases of legs IV, sometimes connected to each other medially as a transverse apodeme, not uniting anteriorly with apodemes 3–4; leg III with femur and genu separate or usually fused.

LARVA. Prodorsum with three pairs of simple or slightly barbed setae, alveolar pits of v2 posterolaterad or laterad of normally developed setae v1; setae sc1 similar in form to v1, and more widely spaced from each other than sc2; setae sc2 similar in length or considerably longer and more attenuate than v1, sc1, but shorter than transverse interval between their insertions. Tergites C, D, EF each entire, their setae collectively slightly barbed; EF not extended posteriorly over HPs; cupules ia, im, ih usually discernible on D, E, HPs, respectively; HPs formed as ventroterminal capsule, wider than long ventromedially; setae h1 and h2 simple, short to exceedingly long, attenuate, similar in length; two pairs of ps setae short to exceedingly long, sometimes dissimilar in length.

Coxisternal plates I and II fully fused medially; pits 1b and 2b spaced well laterad setae 1a and 2a, respectively. Coxisternal plates III with setae 3a and 3b attenuate, short to exceedingly long.

Legs. Ambulacrum of leg I of adult female and male well-developed but lacking claws; that of larva similar, but sometimes with rudiments of paired claws. Leg I with tibia and tarsus of adult male and larva separate or more often fused, as in adult female. Ambulacra of legs II and III of adults and larva with empodium and symmetrically paired claws. Tarsi II and III lacking any spinelike projection over base of ambulacrum. Femora I and II lacking flanges. Legs I–III moderately short, stubby, with no segments elongated; on leg II, combined length of genu and tibia exceeding length of tarsus, and equal to that of femur. Leg III of adult male not enlarged; femur and genu coalesced into one segment, as in female, or separate. Leg IV of adult female elongate-cylindrical, with femorogenu somewhat longer than tibiotarsus, femorogenu with 0–2 setae, tibiotarsus with two setae; trochanter moderately thick, subtriangular or subquadrate, shorter than femorogenu, with or without seta. Leg IV of adult male short, stubby, with or without a short seta on trochanter; femorogenu shorter than trochanter, lacking flanges, and with zero or one short seta, Ge -vʹ; tarsus, if present, bearing three setae and small claw, or more usually absent or rudimentary such that prominent tibial solenidion and sometimes one or two tibial setae retained as terminal structures, with tibial seta vʹ short or attenuate.

Number of setae and solenidia on legs in adult female as presented in Table 1 and as follows: femur I with 2–4 setae (lʹ rudimentary if present, d small or rudimentary if present, lʹʹ rudimentary or developed, vʹʹ developed); femur II with 1–3 setae (vʹʹ developed if present, d small or rudimentary if present, lʹ rudimentary if present); femur III without setae; genua I–II with or without four developed setae, genu III with three setae (lʹ, l″, vʹ) or without setae; tibiotarsus I with 5(+ φ1)+5(+ ω) phaneres, lacking solenidion φ2 and seta k″; tarsal seta s spine-like, setae tcʹtcʹʹ eupathidial, setae ftʹ-ft″ absent or indicated by alveolar vestiges; tibiae II–III with four setae; tarsus II with 4(+ ω) to 5(+ ω) setae, seta uʹ spine-like, often bifid apically, seta uʹʹ present or absent; tarsus III with 4 or 5 setae, seta uʹ spine-like, often bifid apically, seta uʹʹ present or absent.

Adult male setation similar to female, but with variation noted in Table 1 and as follows: tarsus I with developed eupathidial setae ftʹ-ftʹʹ, tarsi II–III sometimes with uʹʹ absent in female but present in male.

Larval setation similar to female, but with variation noted in Table 2 and as follows: tarsi II–III with seta pʹ present in larva but absent in adults; tarsus III with seta uʹʹ present in larva, usually retained in adult male and female; tarsi II–II without seta pvʹ, added in adult male and female.

Etymology. The prefix podo- (Gr. foot) refers to the distinctive, well-developed ambulacra of these mites that bear small claws on legs II–III but not leg I (excepting the larvae of two species). Few other tarsonemid mites have lost the claws on leg I but retained them on legs II–III, and all other acarapine mites have large, well-developed claws on legs I–III. The suffix -tarsonemus refers to the thread-legged aspect of leg IV of adult females of this genus, which resembles that of other members of the family Tarsonemidae . The name is also intended to indicate the morphological and ecological similarities of these mites with those of both families Podapolipidae and Tarsonemidae .

Remarks. The designation of setae on tarsi II–III is problematic, showing differences between species, but also in ontogeny and sex. All active instars have three consistent setae, the tectal pair tcʹ-tcʹʹ and the spine-like unguinal seta uʹ, plus the tarsal solenidion on leg II. As in other Tarsonemidae , seta pvʹ on tarsi II–III is expressed in the adult. In addition to these, the larvae of all species have a tiny apical anterolateral seta, designated pʹ, on tarsi II–III; and most species have a posterolateral seta, designated u″, on tarsi II and III. Seta pʹ is not expressed in the adult instar, and seta u″ is sometimes lost.

As seta pʹ is present in the larva, then lost, and seta pvʹ is present only in adults, they could be considered homologous. However, seta pvʹ is situated subapically and is as long as the tectal setae, in contrast to the short, apically positioned larval seta pʹ.

Seta uʹʹ is present in the larvae in all but the Bolivian species on tarsus II and in all species on tarsus III. However, seta u″ on tarsus II is lost in the adult male and female of the South African species and, on tarsus III, on the adult female of the Bolivian species; another species from Ecuador, for which the larva is unknown, lacks seta u″ on tarsus III in both sexes ( Table 2).

The interpretation of the eupathidial pair added to the adult male as (ft) is based on (a) no example of the other eupathidia being suppressed or added in a sexually dimorphic way ( Lindquist 1986, p. 153); (b) their position near the solenidion and the absence of well developed eupathidia in a typically proral position; (c) the addition of (ft) as eupathidia in at least two genera of pseudotarsonemoidines, i.e. Pseudotarsonemoides and Ununguitarsonemus ( Khaustov 1998; Lindquist 1986, respectively).

The fusion of tibia and tarsus I in the larva and adult male of most species is also unusual, as these are separate in other Tarsonemidae . One Australian species retains the typical, plesiomorphic condition of separation in the adult male and larva, and the Indian species has separate segments in the larva but not the adult male. This progression from fusion only in the adult female to fusion in all life stages is unique in the Tarsonemidae .

Finally, the structure of the respiratory system of Podotarsonemus is mostly uniform throughout the genus, with one notable exception (the species from India). In most species the system is paired, with each stigma leading to a single trachea that runs into a very lightly sclerotized atrium. Distally, each trachea emerges from the atrium and leads into a more sclerotized post-atrial structure that usually appears to have one edge more sclerotized than the other. Distally, two tracheae emerge from the post-atrial structure, but these are not always apparent (e.g., Figs 15A–C ). The Indian species differs in having an unpaired atrium and a single, sclerotized tube emerging distally from each of its heavily sclerotized post-atrial structures ( Fig. 17 ).

Figures

FIGURE 15. Podotarsonemus boliviensis sp. nov. female. (A, B) respiratory system; (D) Plates C and D, aberrant specimen. Podotarsonemus ecuadorensis sp. nov. (C) respiratory system.st = stigmata, at = atrium, pa = post-atrial chamber.

FIGURE 17. Podotarsonemus indicus sp. nov. female, respiratory system.st = stigmata, at = atrium, pa = post-atrial chamber.