Argynnia retorta (Leidy) Stepanek 1953
Nebela collaris var. retorta Leidy 1879
Non Cyphoderiopsis longicollis Playfair 1917

Diagnosis: Shell elongated, curved or retort-shaped, rarely straight, not or little compressed; fundus rounded regularly; pseudostome circular, without lips or flanges. Shell composed of irregular non overlapping polygonal or circular plates, sometimes with rod shaped elements; the plates around the pseudostome are relatively large.

Dimensions: My measurements: L 120-138 µm mean 130.2 µm (n=7); Leidy (1879): L 144 µm (n=1); Chardez (1958): L 128-140 µm, Ø 58-70 µm, Ø pseudostome 20-25 µm (n=3); Hoogenraad and De Groot (1952): L 140 µm; Wailes (1912): L 130-170 µm.

Habitat: Mosses and freshwater. I found this species in moss from a freshwater pond in permafrost near Nuuk, Greenland, collected by Maria Holzmann in 2018. Other reports are from North-America (Leidy, 1879; Hoogenraad and De Groot, 1952; Wailes, 1912), Indonesia (Hoogenraad and De Groot, 1942), Czechoslovakia (Stepanek, 1953) and Belgium (Chardez, 1958).

Remarks: I don’t agree with Chardez that Cyphoderiopsis longicollis Playfair, 1917 is the same species as A. retorta. The species which he found in Australia is half the size of the specimens observed by Leidy, Stepanek, Hoogenraad and De Groot and Chardez.

Leidy wrote: Variety A. retorta, a peculiar form for the first time observed; a single specimen as represented in the woodcut on page 151; Shell retort-form, or resembling in shape that of Cyphoderia ampulla, but in structure characteristic of Nebela, being composed of circular disks of variable size length 0.144 mm.; greater breadth 0.072 mm.; loss breadth 0.036 mm. ; greater breadth of mouth 0.027 mm.