Sejus americanus (Banks, 1902)

Walter, David Evans, 2013, A new genus and family of sejine mites (Acari, Parasitiformes, Mesostigmata, Sejoidea) based on new species from Lord Howe Island and Brazil, and a redescription of Sejus americanus (Banks, 1902), Zootaxa 3691 (3), pp. 301-323 : 315-320

Sejus americanus (Banks, 1902)

Figures 36–47

Specimens examined. Canada, Alberta: One female, ex meadow soil and litter in aspen parkland (53°39' 27”N, 112°46' 01”W), 11 km S Lamont, Lamont Co., Alberta Canada, 27 May 2007; 2 males same data but litter under shrubs, 13.v.2007; 3 females ex polypore sporocarps on aspen logs (53°39' 24”N, 112°45' 34”W), 16 July 2011; 1 female, 2 male, 1 deutonymph ex litter, moss, rotten wood under brush pile (53°39' 24”N, 112°45' 34”W), 15 June 2012, D.E. Walter & H.C. Proctor; 2 females, 1 male Ecosystem Management Emulating Natural Disturbance Project (EMEND), NW Peace River (56° 46' 13'' N,– 118° 22' 28'' W), 25–940, 83–892, 63–889, I. Diaz. Quebec: 2 females, 1 male ex white spruce, Harrington, C.I.P. Tree Farm, 9 June 1965, R.M. Emberson. New Brunswick: 1 female, 1 male ex deciduous litter in depression, Kouchibouguac National Park, Kent Co., 27–29 September 1977, I.M. Smith; one female same data except beneath bark of fallen beech branch, 26 July 1978. USA: Minnesota: 2 females, in rotten wood, Anaka Co., 19 April 1941, G. Kretzschmer. All in the Canadian National Collection.

Diagnosis. Adults large (adult idiosoma 900–1100 long along midline). Cuticle sticky, with adherent soil particles; soft cuticle plicate and with numerous small (5–6) denticles ventrally, laterally; dorsal shields ornamented with large, rounded tubercles ( Figs 36 , 44 ); peritrematal shield broad, joined to podonotal shield anteriorly; peritreme on ventral margin of shield extending from between coxae III–IV to near juncture podonotal shield. Posterior horn-complexes each formed of inner and outer horns with distal seta and separated from other shields by soft cuticle; outer horn conical with long (~100) stalk bearing stout (125 long), densely barbed seta with spatulate, membranous tip (flame seta); ~4 small (20–25) subdistal (midpoint to near base of flame seta) barbed setae; 4 longer (38–56) densely barbed setae on outer margin, dorsal and ventral poroid; inner projection short (~35) with stout (105 long) densely barbed seta with spatulate, membranous tip. Postanal seta on strong apophysis ( Fig. 40 po). Gnathotectum with sparsely denticulate margin and strong median and lateral processes ( Fig. 46 ); palpal apotele with two tines and strong basal spur ( Fig. 43 ), palpal setation normal, lateral setae of palptibia with subdistal spur; chelicerae serrate ( Fig. 42 ), fixed digit with 9–10 teeth (including Gabelzahn), short (7), simple pilus dentilis; movable digit with double row of numerous small teeth; deutosternal gutter with numerous rows of 4–6 denticles, patches of ~12 denticles on subcapitulum between sparsely barbed palpcoxal setae (~60 long); h1 and internal malae membranous ( Fig. 41 ); anterior (h3 ~60) and posterior (h2 ~110) hypostomal setae simple; corniculi (30 long) horn-like; tritosternal base (50 long) columnar, laciniae divided distally, base broadened (60) with a pair of lateral conical teeth ( Fig. 38 , arrowed). All legs with paired claws, segments ornamented with short rows of denticles; most setae set on short tubercles, strongly barbed, ending in flame-shaped, membranous tips; basitarsi II–IV with ventral gland opening adjacent to peripodal fissure, ventral setae smooth; telotarsi II–III each with ~6 trident setae ( Fig. 47 ) and nude intercalary sclerite; setae of intercalary sclerite of tarsus IV simple, av4 (65) about 50% longer than pv4 (40); tarsus I with apicotarsus. Setation of coxae I–IV: 2-2-2-1; trochanters I–IV: 6- 5-5-5; femora I–IV: 13-11-6-6; genua I–IV: 12-12-12-11 (2-3/1, 3/1-2; 2-3/1, 3/1-2; 2-3/1, 3/1-2; 2-3/1, 3/1-1); tibiae I–IV: 13-11-11-11 (2-3/2, 3/1-2; 2-2/1, 3/1-2; 2-2/1, 3/1-2; 2-2/1, 3/1-2).

Female. Sternal setae ( Fig. 38 ) simple, st1 and st2 each on small platelet with lyrifissure on posterior margin (stp1 – 2, respectively); st2 and st3 – 4 inserted on small, indistinct platelets. Endopodal elements III–IV fused, narrow, bearing stp3 anteriorly. Genital shield microtuberculate, rounded (180 long, 200 wide) with four pairs of simple marginal setae, one pair of lyrifissures in posterior corners, anterior notch shallow; internal median flaskshaped sclerotisation ( Fig. 37 ) supporting spermatheca. Ventral setae on small, raised platelets or larger platelets with 1–2 dermal gland openings, simple anteriorly, becoming longer and densely barbed posteriorly; metapodal plates (115 long, 95 with) rounded-subtriangular, tuberculate, and with median dermal gland opening; ventri-anal shield projecting anal opening ventrally, postanal seta (55) on short tubercle (~10), densely barbed and with modified tip. Podonotal shield (450 along midline) truncate posteriorly, joined to peritrematal shields anteriorly with large, raised median region ( Fig. 36 ); two pairs of mesonotal scutellae, anterior longer and narrower than posterior; pygidial shield oval (340 across) with ~ten pairs of setae, tuberculate anteriorly and medially, extended anteriorly to between posterior mesonotal scutellae by irregular field of dark, lightly sclerotised cuticle.

Male. Similar to female except smaller and more extensively sclerotised, opisthonotal shield ( Fig. 44 ) covering region, without separate scutellae or pygidial shield; ventri-anal shield with irregular anterior margin, extended laterally to capture metapodal plates ( Fig. 45 ); sternitigenital shield (260) bearing four pairs of simple setae, three pairs of lyrifissures; genital opening subcircular (55 long), covered by two nude valves, between coxae II.

Remarks. Banks’ (1902) description and illustration are sketchy, but the large size (Banks says 1.5 mm, but presumably this includes the horns and gnathosoma), the distinctive median ridge on the podonotal shield, and the northern distribution (Olympia, Washington, St. Croix Falls, Wisconsin) all suggest that the Alberta mites are S. americanus . The type specimen appears to be lost (on loan from the Museum of Comparative Zoology at Harvard to Ohio State University), but specimens identified as S. americanus from the Canadian National Collection appear to be the same species as the Alberta mites.

The adults of Sejus americanus are easily distinguished from the only other described species of the genus in North America, S. carolinensis Lekveishvili & Klompen (2004) . For example, S. americanus has a 3-pronged tectum (vs triangular in carolinensis ), a double row of teeth on the moveable digit (vs one row), an anchor-shaped tritosternum (vs sickle-shaped), a female genital shield with four pairs of setae and a pair of pores in the posterior corners (vs three pairs and pores on midline), a much broader ventri-anal shield, and the posterior horns are separated from the pygidial and ventri-anal shields by soft cuticle. However, S. americanus is closely related to the type species of the genus, S. togatus C.L. Koch, 1836 , a somewhat variable species (Gwiazdowicz & Gulvik 2009), and further comparisons between the species might be profitable.

Figures

FIGURES 36 – 37. Sejus americanus (Banks, 1902) adult female (light micrographs). 36 Dorsum of female. 37 Venter of female. Scale bar = 500 µm.

FIGURES 38 – 40. Sejus americanus (Banks, 1902) adult female. 38 Venter subcapitulum and sterno-genital region (arrow points to anchor-shaped tritosternum). 39 Legs III, IV, metapodal plate (arrow). 40 Ventri-anal shield with postanal seta (po). Scale bars = 50 µm.

FIGURES 41 – 43. Sejus americanus (Banks, 1902) adult female. 41 Hypostome showing membranous seta h 1. 42 Fixed and movable digits of chelicera. 43 Palptarsal apotele (arrow points to spur, middle tine ~ 25 µm long). Scale bars 41 = 10 µm, 42 = 50 µm.

FIGURES 44 – 47. Sejus americanus (Banks, 1902) adult male. 44 Dorsum of male. 45 Venter of male. 46 Gnathotectum. 47 Leg II with trident setae on tarsus. Scale bars 44 – 45 = 500 µm; 46 – 47 = 50 µm.