Difflugia gigantea Schlumberger, 1845
Diagnose: Shell ovoid, elongated, narrowed in front, almost pyriform, sometimes slightly depressed; covered with large grains of sand forming an irregular outline; this species resembles Difflugia pyriformis, but it differs in its more elongated form and in its greater size.
Dimensions: Schlumberger: 80-230 µm. My measurements: length 322-554 µm.
Ecology: Freshwater, in sediment of mesotrophic water types, and between sphagnum.
Remarks: Schlumberger’s measurements (80-230 µm) are, in light of our current knowledge, not really a reason to call this species “gigantea”, as much larger shells have been reported, e.g. the one atop of this page. The name “gigantea” was also used by Didier Chardez in a publication (1967) where he introduced, in his words, “Difflugia oblonga v. gigantea LEIDY, Thèque semblable à l’espèce, mais plus grande, 450 à 580 µ” (= Test resembling the type, but much larger, 450 to 580 µm), without any further comment or reference to a specific date, description or drawing of Joseph Leidy. This variety was elevated to species rank by Ogden and Fairman (1979). In 1984 Chardez, probably unaware of the Ogden and Fairman publication, also ranked his variety to species status, now referring to the test of 580 µm on Plate X, fig. 15 in Leidy, 1879. However, the name gigantea had already been used, and therefore preoccupied by Schlumberger in 1845, who described his Difflugia gigantea as follows:
Animal with brownish-blue test, as if covered with large grains of sand forming irregular projections; ovoid, elongated, narrowed anteriorly. Length 0.08 to 0.23; greatest width, 0.036 to 0.05. This species resembles Difflugia proteiformis, Ehrb.; but it differs in its more elongated form (narrowed in front, almost pyriform, sometimes slightly depressed) and in its greater size. Pseudostome circular, with irregular edge, gives passage to three or four thick and obtuse cylindrical expansions (=pseudopodia), thick, which in contraction, are covered with small bulges.
It is not clear which unit of measurement was used by Schlumberger, but it is plausible that he used the millimeter if it is compared with the length of Sphenoderia lenta in the same publication. Schlumberger gives a measurement of 0.04-0.05 for that species and that fits fine if the unit is millimeter: 40-50 µm.
In older text the unit “lines” is used. A line is 1/12 of an inch, so 0.08 would be 169 micrometres. In that case his shells were 168-483 µm long and 75-105 µm broad. If he used the French “ligne” (line), based on the French inch, so the conversion is a little different. A “ligne” is 2.2558291 mm, so roughly the shells are 180-518 µm. However, at the same time, Ehrenberg (1938) gives a length of 1/18 “Linie” (=line) for his D. oblonga, and he writes that 1/300 mm = 1/676 Linie. His (German) Linie = 2.253333, so the difference is not large compared with the French line.
There is no clear match between the shells of Leidy, Chardez and Ogden. Chardez gives two different sizes, the measurements published in 1967 are different from those published in 1984. Ogdens shell strongly resembles test a.
Following dimensions given for D. gigantea sensu Chardez, 1967 and Ogden and Fairman, 1979: Chardez (1967): 450 – 580 µm; Chardez (1984): length 450 – 462 µm; Ogden and Fairman (1979): 341 – 480 µm; Lahr & Lopes (2006): 180 – 280 µm.
The name D. gigantea (Chardez, 1967) Ogden et Fairman, 1979 is not valid.