Megisthanus manonae, Seeman, 2019

Seeman, Owen D., 2019, The megisthanid mites (Mesostigmata: Megisthanidae) of Australia, Zootaxa 4563 (1), pp. 1-40 : 14-17

Megisthanus manonae sp. nov.

Figures 6–7

Material examined. Australia, Queensland, ex Mastachilus australasicus (Northern form): Holotype female, Pelion State Forest, 21.077°S 148.688°E, 17.iii.2014, C. Burwell, sampcode #36348 ( QMS 109476 ). In QM. Paratypes: 1 female ( ANIC 51-006450 ) , 1 major male ( QMS 109478 ), same data as holotype; 1 female, Eungella NP, 21.143°S 148.489°E, 13.xi.2013, C. Burwell, sampcode #25828 ( QMS 109477 ). Holotype and two paratypes in QM ; one female paratype in ANIC .

Diagnosis. Female and male. Sternal setae st4 absent. Seta pd2 of femur IV on rudimentary projection. Dorsal shield finely punctate. Ventrianal shield widest at posterior-level of, or just posterior to, anus. Female. Dorsal shield lyriform, length 2.50–2.55 mm, maximum width 1.05–1.15 mm, tapering to minimum width 420–450, expanding posteriorly to 460–490; shield appears ovate when secondarily sclerotised. Anterior dorsal shield setae sparsely barbed, length 80–150, becoming shorter and more barbed posteriorly; posterior dorsal shield setae short, with numerous large barbs, length 45–70; podonotum and opisthonotum densely setose. Sternogynal shields separate, each bearing 4–6 setae; internal genitalia with well-developed, separate latigynal-mesogynal and vaginal elements. Ventrianal shield subtriangular. Major male. Larger than female, dorsal shield length 2.85 mm, width 1.50 mm, without developed setae; setae on soft cuticle laterad dorsal shield of moderate length, 55–100; 65 setae around genital opening; corniculi without medial inner tooth; setae h1–3 smooth, palp coxal seta barbed.

Description. Female (n = 3). Dorsum ( Figs 6A , 7D ). Idiosomal length ca. 2.6 (2.55–2.80) mm, width 1.35 (1.35–2.00) mm, body length (including gnathosoma , to tip of gnathotectum) 3.30 (3.30–3.50) mm. Dorsal shield lyriform, length 2.50 (2.50–2.55) mm, maximum width 1.05 (1.05–1.15) mm, narrowing to 420 (420–450) then expanding slightly (ca. 40) to 460 (460–490); secondary sclerotisation absent or present laterally and posteriorly; maximum length of dorsal shield including secondary sclerotisation 2.80 mm, width 1.65 mm. Dorsal shield hypertrichous, densely setose, anterior setae sparsely barbed, longer (80–150) than posterior setae, which become shorter (45–70) and more barbed; posterior setae with numerous large barbs ( Fig. 7D ). Dorsal shield cuticle finely punctate, without reticulation. Setae in soft cuticle barbed, on platelets, most setae 180–260, becoming shorter laterally; some setae laterad narrowest part of dorsal shield very long, 550–600.

Venter ( Figs 6B , 7 A-C). Setae st1 170 (130–170), sparsely barbed. Sternal shield ( Fig. 7A ) reticulate, with two pairs of setae, 5–7 pairs of pores opening ventrally, 0–1 pore opening laterally, and one pair of lyrifissures; setae st2–3 sparsely barbed, st2 160 (115–160), st3 105 (90–105), st4 absent; shield medial length 120 (110–125).

Sternogynal shields ( Fig. 7A ) free posteriorly, genital opening length 305 (300–310), width 340 (340–350), each sternogynal shield length 270 (270–280), lineate-reticulate, each bearing 4–6 smooth setae (asymmetrical) and one lyrifissure; anterior setal pair (55–75) slightly barbed and longer and thicker than posterior setae (20–45). Internal genitalia comprise: mesogynal+latigynal element (mg + lg), the latigynal element well-developed as arms with porose areas, articulating with anterolateral margin of sternogynal shield; posteriorly, mesogynal element fused with latigynal element, its tip reaching margin of vaginal arms (va); pyriform vaginal heads (vh); and Ushaped vaginal arms articulating anteriorly with sternogynal processes (sgp) ( Figs 7 B–C).

Ventral shield ( Fig. 6B ) extends 830 (830–920) posteriorly from posterior margin of genital opening; maximum width behind coxa IV 285 (275–290); shield with 13–20 pairs of setae around shield margin, 1 pair posteriorly within shield, and with 1–3 pairs of setae off shield margin close to sternogynal shield; setae smooth, length 35–110; with 3–5 pairs of pores around shield margin posterior of coxa IV, 7–8 pairs of pores within shield, and 1–3 pairs of larger porose areas on shield margin just level with posterior margin of coxa IV; shield reticulate, lineate-reticulate zones limited to posterolateral margins.

Ventrianal shield a rounded triangle ( Fig. 6B ), with anus slightly posterior of centre of shield; anterior width ca.160–180, maximum width posterior to anus, 435 (435–470), length 390 (390–440); shield reticulate; 16–26 loosely paired setae, length 45–115.

Peritrematal shield hypertrichous, post-peritrematal region extends 640 (620–670) behind coxa IV into metapodal region ( Fig. 6B ); setae laterad legs sparsely barbed, length 40–50; three pairs of long setae on anterior margin of peritrematal shield, length 200–300.

Gnathosoma . Gnathotectum reticulate, medial length 760 (760). Subcapitulum with setae h1 275 (275–280), h2 150 (150–175), h3 300 (225–300), pc 185 (175–185), all setae sparsely barbed; subcapitulum finely striate. Corniculi length 265 (250–265) with medial tooth. Palp trochanter with ventro-distal spur, length 25–30 and dorsodistal spine 20, palp femur with distal spur, length 20. Chelicerae with entire fixed digit length 670 (670– 705), movable digit length 380 (380–410). Morphology as per genus description. Fixed digit with 12–14 teeth; cheliceral seta length 30. Movable digit with 10 teeth.

Legs. Setation as per genus description. Selected setal measurements: genu II setae ad1, pd1 subequal, length 100–120; seta pd1 on genu III long (length 500–600), much longer than ad1 (length 150–210), tarsus III ad3 long, length 340–355, femur IV pd1 long, length ca. 500, genu IV ad1 very long, length ca. 750, pd1 ca. 650–700, tibia IV pd1 long, length ca. 550 and tarsus IV ad4 long, length ca. 470, pd3 long, length ca. 360. Femur IV with rudimentary projections bearing setae pd2, ad2, larger projection bearing ad3.

Male (major) (n = 1). Dorsum. Idiosomal length 3.05 mm, width 1.85 mm, body length (including gnathosoma , to tip of gnathotectum) 3.90 mm. Dorsal shield ovate, length 3.85 mm, width 1.50 mm; secondary sclerotisation absent. Dorsum hypertrichous. Most setae on dorsal shield tiny, smooth, length <5; some anteromarginal setae longer (45–120). Setae in soft membrane close to anterior dorsal shield sparsely barbed, moderate length (55–100), lateral setae barbed short (20–50).

Venter. Setae st1 barbed, length 165. Sternoventral shield reticulate, length from posterior margin of genital opening 1110. Sternal setae st2 and st3 barbed, st2 not measureable, st3 80; sternoventral shield hypertrichous posterior to setae st3, with ca. 65 setae around genital opening; posterior sternoventral shield with setae along margin; these setae smooth to sparsely barbed, shortest setae 40 (near genital opening) and longest setae 120 (posterior to coxa IV); posterior sternoventral shield with two large discs of porose cuticle (diameter 120), each bearing an anterior (70) and posterior pair (100) of unmodified smooth setae, and a highly modified pair of setae centrally (80); unpaired seta between discs.

Genital opening length 150, width 130, surrounded by a ring of sclerotised cuticle; this cuticle with 13–14 pairs of loosely paired pores laterad genital opening.

Ventrianal shield a curved trapezoid, length 395, anterior width ca. 420, maximum width 575, widest posterior to level of anus; shield reticulate, with 25 setae. Peritreme and peritrematal shield similar to female.

Gnathosoma . Gnathotectum similar to female, medial length 870; subcapitulum similar, except with submedial projections (inner length 40). Setae h1 smooth, blade-like, 225; setae h2 smooth, 155, setae h3 barbed, 190, palp coxal seta barbed, 205. Corniculi without tooth-like process, corniculi length 390. Palp difficult to see, but cusps present. Chelicerae similar to female.

Legs. Similar to female, distal spurs and spines similar in size.

Etymology. It is with great pleasure that I name this species for Dr Manon Griffiths, a dear friend of the author and also the collector of this species, Dr Chris Burwell.

Differential diagnosis. This species is closely related to M. leviathanicus because it shares the lyriform dorsal shield and a distinct latigynal element. It is most easily distinguished from M. leviathanicus by the form of the posterior idiosomal setae: those of M. manonae have numerous barbs of moderate size ( Fig. 7D ), while those of M. leviathanicus have one or two large barbs ( Fig. 7E ). The males cannot be reliably distinguished, although the corniculi (390 vs 470-560) and setae h3 (190 vs 335-375) of M. manonae are shorter ( Table 1).

Remarks. This species was found in the rainforests of middle-eastern Queensland, in contrast to M. leviathanicus , which occurs in the rainforests of the wet tropics of northern Queensland. These rainforest regions are separated by an expansive warm, dry region (the Burdekin Gap; see for example Moritz et al. 2005). Although represented by only two collections, I suspect M. manonae will be restricted to middle-eastern Queensland.

Figures

FIGURE 6. Megisthanus manonae sp. nov., female, photomicrographs. (A) dorsum; (B) venter. Scale bar = 200 µm.

FIGURE 7. Megisthanus manonae sp. nov., female. (A) sternogenital region; (B) internal genitalia, fused mesogynal and latigynal shields (mg+lg), position of sternogynal setae indicated by dotted circles; (C) vaginal heads (vh) and vaginal arms (va), which articulate with sternogynal processes (sgp) arising from thickened sternogynal margins (sgm); (D) posterior dorsal shield setae. Megisthanus leviathanicus Seeman, 2017, female. (E) posterior dorsal shield setae.