Megisthanus simoneae Seeman 2019, sp. nov.
Creators: name: Seeman, Owen D.
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Mesostigmata
Megisthanidae
Megisthanus
Megisthanus simoneae

description: Megisthanus simoneae sp. nov.
Figures 8–11
Material examined. Australia, Queensland, ex Mastachilus polyphyllus (W.S. Macleay, 1826). Holotype female, Barakula Forest Station, cypress forest, 26°26′S 150°30′E, 10–16.x.2004, C. Burwell & S. Wright, sampcode #52067 (QMS 109479). In QM. Paratypes. 2 females (QMS 109480; ANIC 51-006451), 1 major male (QMS 109481), same data as holotype. 2 females, 1 major male, Burleigh Heads, 3.x.1964, J. McMaster, under elytra of pinned beetle (QMS 109482–4). All in QM except one female 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 anterior level of anus. Female. Dorsal shield ovate, length 1.80– 2.15 mm, maximum width 0.95–1.20 mm, not including secondary sclerotisation. Anterior dorsal setae comprising short (40–70) dorsal setae intermingled with longer (140–225) sparsely barbed setae; both types becoming longer posteriorly; podonotum more setose than opisthonotum. Sternogynal shields separate, each bearing 3–5 setae; internal genitalia with rudimentary latigynal element. Ventrianal shield moderately reniform. Major male. Broader than female, dorsal shield length 2.30–2.40 mm, width 1.35–1.45 mm, without well-developed setae; setae on soft cuticle laterad dorsal shield short, length 10–25; 20 setae around genital opening; corniculi with small medial inner tooth; setae h1–3 smooth, palp coxal seta barbed.
Description. Female (n = 4). Dorsum (Figs 8A, 9A, 11A). Idiosomal length ca. 2.45 mm (2.30–2.65 mm), width ca. 2.00 mm (1.60–2.20 mm), body length (including gnathosoma, to tip of gnathotectum) ca. 3.10 mm (2.90–3.30 mm). Dorsal shield ovate, length 1.80 mm (1.80–2.15 mm), width 0.95 mm (0.95–1.20 mm); secondary sclerotisation present, extensive (Fig. 8A) laterally and posteriorly; maximum length of dorsal shield including secondary sclerotisation 2.35 mm (2.20–2.40 mm), width 1.80 mm (1.45–2.05 mm). Dorsal shield hypertrichous, densely setose. Podosomal part of dorsal shield with numerous short (40–70) barbed setae, intermingled anteriorly with long (140–225) sparsely barbed setae; opisthosomal part of dorsal shield with longer setae of both types, i.e., a shorter barbed seta (to 140) and long setae (200–525); longest setae posteromarginal. Dorsal shield cuticle appearing smooth, with inconspicuous fine punctation. Setae in soft cuticle barbed, on small platelets, length 150– 500, longer posterolaterally.
Venter (Figs 8B, 9 B–C). Setae st1 130 (130–180), barbed. Sternal shield (Fig. 9B) reticulate, with two pairs of setae, 4 (4–9) pairs of pores opening ventrally, 0–1 pores opening laterally, and one pair of lyrifissures; setae st2–3 sparsely barbed, st2 65 (85–105), st3 60 (60), st4 absent; shield medial length 95 (95–115).
Sternogynal shields (Fig. 9B) free posteriorly, genital opening length 235 (235–260), width 275 (275–290), each sternogynal shield length 210 (210–240), weakly lineate-reticulate, each bearing 3 (3–5) setae and one lyrifissure; anterior setae barbed, longer (40–50) than smooth posterior setae (10–40). Internal genitalia comprise three obvious elements (mg, va, vh) and rudimentary latigynal (lg) elements, which are represented by small porose area on thickened ventral shield margin, near attachment of vaginal arms with sternogynal shield.
Ventral shield (Figs 8B, C) extends 710 (710–870) posteriorly from posterior margin of genital opening; maximum width behind coxa IV 350 (350–420); shield with 9–10 (7–10) pairs of setae around shield margin, with or without one pair posteriorly within shield (holotype, just within margin), and with 0–2 pairs of setae off shield margin close to sternogynal shield (often asymmetrical); setae smooth, length 40–95; shield mostly reticulate, small lineate-reticulate region at level just behind coxa IV.
Ventrianal shield moderately reniform (Fig. 8D), with anus mostly in posterior half of shield; anterior width ca. 340 (340–400), maximum width anterior to anus, 475 (450–540), length 295 (395–320); shield reticulate; 8–14 loosely paired setae, length 75–90 (60–80).
Peritrematal shield hypertrichous, post-peritrematal region extends 385 (385–450) behind coxa IV into metapodal region (Fig. 8B); setae laterad legs sparsely barbed, length 25–60, those directly above legs III–IV much shorter than other setae; three pairs of long setae on anterior margin of peritrematal shield 240–340.
Gnathosoma (Fig. 10A). Gnathotectum reticulate, medial length 620 (620–700). Subcapitulum with setae h1 240 (230–265), h2 160 (145–170), h3 broken (275–300), pc broken (165–180), all setae sparsely barbed; medial subcapitulum with some fine striae, hypostome smooth. Corniculi length 235 (235–265) with medial tooth. Palp trochanter with ventro-distal spur, length 25 (25–45), palp femur with distal spur, length 10 (10–15). Chelicerae with entire fixed digit length 610 (610–670), movable digit length 320 (320–380). Morphology as per genus description. Fixed digit with 12–13 teeth; cheliceral seta length 25–30.
Legs (Fig. 9D). Setation as per genus description. Selected setal measurements: genu II setae ad1, pd1 subequal, 95–120; seta pd1 on genu III, 350–490, much longer than ad, 120–150, tarsus III ad3 moderately long, 275–300, femur IV pd1 long, 340–450, genu IV ad1 very long, 530–620, pd1 very long, 550–850, tibia IV pd1 long, 470–600, tarsus IV ad4 long, length 350–400, pd3 long, length 300–315. Femur IV with rudimentary projections bearing setae pd2, ad2, small projection bearing setae ad3.
Male (major) (n = 2). Dorsum (Fig. 8E). Idiosomal length ca. 2.80–3.10 mm, width ca. 2.20–2.40 mm, body length (including gnathosoma, to tip of gnathotectum) ca 3.55–3.75 mm. Dorsal shield ovate, length 2.30–2.40 mm, width 1.35–1.45 mm; secondary sclerotisation present, extensive. Dorsum hypertrichous. Setae on dorsal shield tiny, smooth, length <5. Setae in soft membrane close to dorsal shield smooth, small (10–25), becoming more barbed and longer laterally, length to 125; some setae near posterolateral and posterior margin of shield also long (to 120).
Venter (Fig. 9E). Setae st1 barbed, length 175. Sternoventral shield reticulate (with some lineate-reticulate patterning behind coxa IV), length from posterior margin of genital opening 900. Sternal setae st2 and st3 barbed, length 85–135; sternoventral shield hypertrichous posterior to setae st3, with 20 setae around genital opening; posterior sternoventral shield with setae along margin; these setae smooth, shortest setae 65 (mesad coxa IV) and longest setae 120 (posterior to coxa IV); posterior sternoventral shield (Fig. 8E) with two large discs of porose cuticle (diameter 90–100), each bearing an anterior and posterior pair of unmodified pair of smooth setae 65–70, and a highly modified pair of setae centrally, length 85.
Genital opening (Fig. 9E) length 125–135, width 115, surrounded by a ring of heavily sclerotised cuticle; this cuticle with 12–13 pairs of loosely paired pores laterad genital opening.
Ventrianal shield (Figs 8E) a curved trapezoid, length 300–310, anterior width ca. 420–440, maximum width 545–560, widest just anterior to anus; shield reticulate, with 12–14 loosely paired setae. Peritreme and peritrematal shield similar to female.
Gnathosoma (Figs 10B). Gnathotectum similar to female, medial length 740–770; subcapitulum similar, except with submedial projections (inner length 30–40). Setae h1 smooth, blade-like, 205; setae h2 smooth, 170, setae h3 smooth, 275, palp coxal seta barbed, 210. Corniculi with small medial tooth-like process, corniculi length 350–360. Palp trochanter with distoventral cusps on trochanter (length 30) and femur (length 30). Chelicerae similar to female.
Legs. Similar to female except distal spurs and spines larger, and small spurs on femur and genu I.
Etymology. It is with great pleasure that I name this species for my niece Simone West.
Differential diagnosis. Megisthanus simoneae is most similar to M. thorelli in having females with two distinct types of setae on the dorsal shield, one being long with few barbs, the other being short and heavily barbed. The two species are most easily separated by the form of these shorter setae, a feature most apparent on the midopisthonotum. In M. simoneae, the shorter setae appear as shorter and more barbed versions of the long setae (Fig. 11A), but in M. thorelli the short setae are even shorter, thicker and more densely and strongly barbed (Fig. 11B).
Remarks. Megisthanus simoneae is found on Mastachilus polyphyllus, a passalid species infrequently collected from south-east Queensland. Records tend to be from relatively drier forests compared to the preferred rainforest habitats of many passalid species, including the host species of M. thorelli, the putative closest relative of M. simoneae.
description: Published as part of Seeman, Owen D., 2019, The megisthanid mites (Mesostigmata: Megisthanidae) of Australia, pp. 1-40 in Zootaxa 4563 (1) on pages 17-22, DOI: 10.11646/zootaxa.4563.1.1, http://zenodo.org/record/2600858