Difflugia urceolata Carter, 1864
Diagnosis: Shell large, broad ovoid or spherical. Aperture circular, large; with a more or less pronounced recurved collar, extending as a broad rim. Shell composed of mineral grains or diatom frustules, often mixed, cemented together with organic material. In sphagnum the test can be nearly completely chitinous, due to lack of mineral material. Multinucleate, 8-60 nuclei; nuclei granular. Shell generally without spines, but a variety, D. urceolata var. olla Leidy, possesses a few short stubby spines developed from the fundus.
Dimensions: In literature 150—550 µm long. Ogden (1980): 137—171 µm (n=26). My observations: 235—280 µm, nuclei 13.8—30.4 µm.
Ecology: in ooze of ditches, ponds, and water with sphagnum contact. Sometimes abundant.
Remarks: In cells which I squeezed for counting and measuring the nuclei I usually found 10 – 20 nuclei per specimen. Nuclei are difficult to count, because some are hidden by the xenosomes. Once I found nuclei which were larger than average and showed a different structure (Fig. 2, left). Penard (1902) gives an average of 40 – 60 nuclei per specimen, with diameters varying between 15 and 26 µm.
Following varieties and forms have been described:
Difflugia urceolata olla Leidy, 1879
Shell with a few short stubby spines developed from the fundus. I found this variety several times between specimens without these ‘spines’. Probably it is one and the same species.
Difflugia urceolata sphaerica Playfair, 1917
Differs from the typical shape in a rounded shape. The length of the shell is 250-300 microns, the width of the shell is 250-300 microns, the diameter of the mouth is 70-120 microns.
Difflugia urceolata lageniformis Wallich, 1864
It differs from the typical form of a very large collar turned out. The length of the shell is 240-380 microns, the width of the shell is 250-285 microns, the diameter of the mouth is 125-200 microns.
Difflugia urceolata minor Deflandre, 1926. Differs from the typical form in smaller sizes. The length of the shell is 166-170 µm, the width of the shell is 116-118 µm, the diameter of the mouth is 72-80 µm.
