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Difflugia difficilis
D. difficilis, from Hartwerd, Netherlands, 2021

Difflugia difficilis Thomas, 1954

Diagnosis: Test ovoid, circular in cross-section. Aboral end of the test commonly with a not prominent, but rounded and/or compressed protuberance, sometimes replaced by a foreign body (diatom) which acts as the absent horn. The sides of the test converge towards the pseudostome to end in a short collar; the pseudostome is circular with a diameter varying between one-half and two-thirds of the width of the test. Test hyaline, clear, coated with siliceous particles, arranged regularly. Nucleus vesicular, spherical, with one central nucleolus. Zoochlorellae present.

Dimensions: Thomas (1954): Length 83-93 µm; width 59-66 μm; aperture 20-27 µm; height of the collar, 6-9 μm.
My measurements:
Naardermeer: L 80-117 µm; W 54-78 µm; aperture 26-32 µm; collar 4.7-7.4 µm high (n=6); nucleus 18.5-22.9 µm (n=2).
Hartwerd: L 119-162 µm; W 85-99 µm; aperture 27-36 µm (n=12); nucleus 31.5-34.2 µm (n=2).
Den Treek: L 111-151 µm (n=20); nucleus 36 µm (n=1)

Ecology: Freshwater, sediment; France (Thomas, 1954), Belgium (Chardez, 1956), Africa (Gauthier-Lièvre et Thomas, 1958), Netherlands (in sediment of mesotrophic and eutrophic waters; 2019-2021).

Remarks: I found three populations which differed in size (see above). The Hartwerd population was found in a ditch near the village of Hartwerd in the nothern part of the Netherlands.

Difflugia difficilis
D. difficilis, after Thomas, 1954.
Difflugia difficilis
D. difficilis, both micrographs show the same shell, turned 90 degrees along the long axis. Length 131 µm, Hartwerd (2021)
Difflugia difficilis
D. difficilis, all shells from the same sample, 90-162 µm (Hartwerd, 2021)
Difflugia difficilis.
Difflugia difficilis
Nucleus, 36 µm – Zeiss 63X 1.4 Oil, and the same nucleus – Leitz 100X 1.3 Oil. Notice the zoochlorellae (Den Treek population).
Difflugia difficilis
Difflugia difficilis
D. difficilis, nuclei, in DIC (Hartwerd population)
Difflugia difficilis
D. difficilis, (Naardermeer, Netherlands, 2019)
Difflugia difficilis
D. difficilis, fundus; the nipple is compressed (here from the broadest side)
Difflugia difficilis
Difflugia difficilis
D. difficilis, with two horns (Naardermeer, Netherlands, 2019)
Difflugia difficilis
Difflugia difficilis
D. difficilis (Naardermeer, Netherlands, 2019)
Difflugia difficilis
Shells 121-151 µm long (Den Treek, Netherlands, 2020)
Difflugia difficilis
Shells 111-130 µm long (Den Treek, Netherlands, 2020).
Difflugia difficilis
This shell has a characteristic collar ornamented with tooth-like particles, with dark triangular particles in between(Den Treek, Netherlands, 2020).
Difflugia difficilis
Difflugia difficilis
Detail of the shell above, collar.
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