Netzelia danubialis (Zivkovich, 1975) new comb.
= Protocucurbitella danubialis Zivkovich, 1975
Diagnosis: test ellipsoid or ovoid, without or with 1-4 hollow horns on the fundus; test in cross-section circular. Collar always well marked and detached from the flanks of the test. In P. coroniformis this character is less well marked, or it does not exist. The test is gray, transparent and encrusted with different mineral particles, in shape and sizes as in some species of Difflugia. Aperture large, circular and crenelated by the diaphragm which is well marked between the big teeth (12-13). The edges of the teeth are bordered by crowns of very fine small grains. Protoplasm has a granulated structure with nuclei and vacuoles. Pseudopodia are characteristic for the peripheral part of the body.
Description: according to Zivkovich: P. danubialis is distinguished from the typical species P. coroniformis by the shape of its test, by the position and number of horns, and by size ratios. In P. danubialis the test is always ellipsoid-ovoid and in its height (H) without the horns the width (D) is H/D=1.4-1.9, while in P. coroniformis the test is more or less spherical and its width is greater or the same or a little smaller than the height H/D=0.7-1.1 (Gauthier-Lièvre and Thomas, 1959). The horns are always placed near the fundus. Their positions vary as follows:
1. The test has a horn which is placed in the center of the fundus.
2. The test has two horns, which are different in their shape and size, and are placed symmetrically near the fundus. The test has two large lateral horns of different shapes and sizes, while the third horn is asymmetrically placed in some specimens; specimens with three similar horns in shape and size can be found.
3. The test has four similar horns, shorter, conical, which are placed in two ranks or in a row. The varieties of the horns of the test confirm that the polymorphism in the new species is highly developed. The most common tests have two horns, while the most rare tests are without horns. Living animals not observed.
Dimensions: Length 230-295 µm, without horns 195-265 μm; width 133-155 μm, pseudostome 70-95 µm, collar 10-20 µm high, H/D 1.4-1.9.
My measurements: Length 208-211 µm, without horns 181-187 μm; width 135-152 μm, H/D 1.2-1.4 (n=3).
Ecology: Freshwater, sediments. Danube, Serbia, Naardermeer, Netherlands.
Remarks: This species was originally placed in the genus Protocucurbitella, in my opinion a highly questionable genus. Its type species P. coroniformis differs from the genus Difflugia in having a diaphragm beneath the teeth that form the collar around the aperture. These so called diaphragm is just an optical illusion! There is no diaphragm behind the teeth, but between them.
I found some tests which resembled N. danubialis very closely. The teeth were ornamented with a kind of bead chain, consisting of a chain of very small xenosomes. This “chain” was also described by Zivkovich (1975): “The edges of the teeth are bordered by crowns of very fine grains”.
On top of each tooth there was a sharp tiny spine present.