Velamentofex berolinensis Völcker and Clauß, 2020
Diagnosis: Trophozoites ovoid, 50-300 µm, with a hyaline, extremely flexible, membranous test. Nuclei numerous, 11.6-16.2 µm in diameter, mean 13.6 µm (n=30), finely granulated, with usually two or three relatively small rounded nucleoli each with one or two lacunae and located just beneath the nuclear membrane. Cytoplasm colorless, yellowish, brownish or greenish, with many vacuoles and numerous small refractive crystalline inclusions, 1.4-2.8 µm long, each attached to a spherical body, ca. 2 µm in diameter. Cells commonly with a layer of hyaline cytoplasm completely surrounding the test. Reproduction by division of the cell body into several cells, or by forming a new cell within the pseudopodial network. Feeds on diatoms and green algae.
Type locality: On waterplants, in 1 m depth, River Havel, Wannsee, Berlin (52°25’47.1″N 13°07’50.0″E), September 2016.
Description: All cells are ovoid with a hyaline membranous test which is very thin and extremely flexible. The cytoplasm is colorless, yellowish, brownish or greenish, and contains many vacuoles and numerous small crystalline inclusions, consisting of a refractive more or less rod-shaped body attached to a spherical non-refractive body, ca. 2 µm in diameter (similar to those in V. saxonensis). Well-fed cells are filled with cytoplasm and also have a layer of hyaline cytoplasm completely surrounding the test. Starving cells often lack surrounding cytoplasm and sometimes it does not even fill the test completely. The test of well-fed cells is not always easy to detect as the inner cytoplasm is difficult to differentiate from that surrounding the cell. The pseudopodial network can be very large, extending some millimeters over the substrate. Sometimes the main cell body is covered by detritus.
Two different modes of reproduction were observed. Most often the main cell body divides into several cells, up to five. Although each new cell has its own peduncle, young cells often share at least parts of the pseudopodial network. Sometimes a second form of reproduction was observed. Within the pseudopodial network a blob of plasma is formed. This blob then forms a new test and a new peduncle. Initially the new cell is connected with the pseudopodial network of the old cell.
Remarks: This species differs from V. tyrolensis and V. saxonensis in size (11.6-11.2 µm vs. 5.1-10.7 µm and 6.5-11.2 µm respectively) and structure (finely granulated nucleus vs. some scattered small nucleoli) of the nuclei.