(Figs. 1–12, 112, 115A)
Type locality. Lemon Creek Glacier, Juneau, Alaska (Christiansen & Bellinger 1980: 768).
Material examined. Alaska: Juneau, mountains between Mendenhall Glacier and Montana Creek trail, 58 o 29 'N, 134 o 40 'W, 14.VII. 1980, on snow 1,300 m., A. Fjellberg leg.; British Columbia: Vancouver Island, Comox Glacier, 49 o 33 'N, 125 o 21 'W, 26.VIII. 1983, on snow 1,950 m., A. Fjellberg leg.; Garibaldi Park, Helm Glacier, 2.IX. 1983, on ice 1,930 m., A. Fjellberg leg.; Washington: Mt. Rainier at McClure, 26.VI. 1976, on snow, J. Edwards leg.; Mt. Rainier at Anvil and Sugarloaf Mountains, 21.VIII. 1980, on snow, A. Fjellberg leg.; Snohomish Co., Columbia Glacier, 30.VII. 2002, on ice, P. Hartzell leg.; Snohomish Co., Honeycomb Suiattle Glacier, 48 o 49 ' 25 ''N, 121 o 37 ' 12 ''W, 12.VIII. 2002, on ice, P. Hartzell leg.; Whatcom Co., Lower Curtis Glacier, 48 o 49 ' 25 ''N, 121 o 37 ' 12 ''W, 6.VIII. 2002, on ice, P. Hartzell leg.; Alberta: Bow Glacier (51.64 o N, 116.51 o W) and Yoho Glacier (51.62 o N, 116.55 o W), summer 2003, P. Hartzell leg.
Redescription. Body size up to 1.2 mm. Body shape cylindrical. Appendages relatively short, in particular the tibiotarsi of the two foremost pairs of legs (Fig. 115 A). Viewed from above the sides of the head with a small angular projection outside the bases of antennae caused by the forwardly directed two anterior ocelli (Fig. 3). Abd. 5–6 almost fused, with a weak break in setal cover. Colour shiny black or violet black apart from the two distal pure white antennal segments. Second antennal segment often paler in distal part. Occipital area of head with two small white spots. Distal part of tibiotarsi pale. Ocelli 6 + 6, the two anterior (A and B) enlarged and placed close to antennal bases, directed forward (Figs. 2–3); ocelli G & H invisible. PAO narrow, almost hidden between antennal base and the two anterior ocelli; only one seta below PAO. Ant. 1 on ventral side with two small apical sensilla and up to 13 elongate sensilla (Fig. 4). Ant. 2 with 2–5 enlarged sensilla in lateral position (Fig. 5). Ant. 3 with up to 7 additional long sensilla in addition to the standard set of 4 dorsal and 3 ventrolateral (Fig. 6). Ant. 4 with simple or bifurcate subapical pin-seta. Erect male sensorial setae not present on antennae. Subapical organite small, peg-shaped. Labrum with 4 / 554 setae, apical edge with 4 small sharp ridges and a composite ventroapical ciliation. Central field of frontoclypeal area with 4 setae. One seta above posterior corner of labrum (Fig. 2). Maxillary palp normally trifurcate with 4 sublobal setae; palps rarely bifurcate, or bifurcate on one side and trifurcate on the other. Labial palps with all papillae and guards present, including guard e 7; terminal setae on papillae short. Hypostomal papilla with H much shorter than h 1 /h 2. Basal fields of labium with 4 median and 5 lateral setae. Head with 4 + 4 (3) postlabial setae. Mandibles normal, with strong teeth. Maxillae unmodified, lamellae covered with fine denticles, Lam. 1 not reaching beyond the 3 -toothed capitulum. Integument smooth, without visible granulation. Body with a uniform ground cover of short smooth setae, becoming slightly longer towards end of abdomen. Macrochaetae weak, not differentiated from ordinary setae apart from their more erected posture; M 1 on abd. 5 is 1.2-1.7 as long as inner edge of last claw. Tergal sensilla short and delicate, distributed as 22 / 11125 (s) and 10 /000 (ms) (Fig. 1). On abd. 1–3 only upper sensillum retained, abd. 5 without anterior sensilla. Abdominal sensilla within the p-row. Ventral tube with 1 + 1 frontal, 3 + 3 lateral and 4–5 caudal setae. Retinaculum with 4 + 4 teeth and 2–4 setae. Manubrium with blunt ventroapical teeth, 1 + 1 (2) short ventroapical setae and fewer than 10 setae in the central ventral field (Fig. 12). Dens crenulated, with 7 (6) dorsal setae in proximal 1 / 3 and a subapical microseta (Fig. 7); ventroapical seta not prolonged. Mucro short and curved, with 5 sharp teeth, no lateral seta. Inner lateral tooth derived from the inner lateral lamella (Fig. 8–9). Tibiotarsi with 11 apical setae (A 1–7, T 1–4). Legs short, in particular tib. 1–2 which have only 3 + 3 setae along the inner median line (as Fig. 72). Claws small, inner and lateral teeth absent; shape narrow, sides constricted towards base (Fig. 10–11). Unguis only slightly longer than unguiculus. Reproductive males with unmodified setal cover (no epitoky).
Discussion. The single species in this genus, originally described as a subgenus of Isotoma, was discovered in Alaska and described by Christiansen & Bellinger (1980: 768). These authors suggested that PAO was absent. However, in well cleared specimens the small PAO is visible and it may be that M. alaskana is a specialised Desoria. Molecular genetics may clear up the relationships. The unusual arrangement of the ocelli, however, is unique in the family although there is a gradual transformation from the normal condition to the arrangement shown in Myopia. Some of the new Desoria species described below show an elongation of the eye-field and "wandering" of anterior ocelli (compare Figs. 18 and 41). The low number of tergal sensilla and the few ventral setae on manubrium in Myopia is unlike most Desoria and may be significant.
The Alberta specimens from Haigh Glacier, Bow Glacier and Yoho Glacier all differ from Alaskan specimens in having three terminal white antennal segments rather than two (Fig. 112). No other consistent differences could be found.
Distribution and ecology. The species appears to be common on glacial ice and snow fields in the Rocky Mountains from southern Alaska to Washington, extending east to Alberta. For details, see above. On Haig Glacier specimens were observed on snow and ice at a density of 5.000–10.000 inds./m 2, covering an area of several hectares. This species could be a North American ecological equivalent to the European "Gletscherflohs" (Desoria saltans Nicolet, 1841).