Observations on

Pyxidicula operculata (Agardh, 1827) Ehrenberg, 1838

Most likely ID: n. a.

Synonyms: n. a.

EOL Phylogenetic tree: Pyxidicula operculata

The overview in Fig. 1 shows a bacterial lawn, a number of circular structures, which on closer inspection are hourglass-shaped, and naked amoebae. The small watch glasses turned out to be shell amoebae (testaceans) from the group of Arcellinida, genus Pyxidicula Ehrenberg 1938.

Figures 2 to 5 show several optical sections through the observed cells. In the group of four in Fig. 2, the focus is on the level of the bacterial layer. In Fig. 3 the focus is on the nuclei. Figure 4 presents the vesicular (ellipsoidal) nucleus with its large central nucleolus together with the contractile vacuoles, next to it an empty shell, where one can even see the fine granulation of the shell material (pseudochitin with sandpaper structure) and its beaded rim. In order to be able to display the surface structure of the shell material and the beaded rim equally sharply, several optical sections were combined using DOF image technology.

Sample from Pond Suploch, Hiddensee (Germany) Latitude: 54.538638, Longitude: 13.097802.

Fig. 1: Overview photo of the surface membrane with              Fig. 2: Pyxidicula operculata amoungst bacteria.
bacterial lawn, shell and naked amoebae.                                Scale bar indicates 10 µm.              
Scale bar indicates 100 µm.                                                           

Fig. 3: Pyxidicula operculata, focused on the level of the          Fig. 4: Pyxidicula with the typical vesicular nucleus and
nuclei (arrow) and the contractile vacuoles (arrowhead).          the two contractile vacuoles next to an empty shell (DOF
Scale bar indicates 10 µm.                                                     image). Scale bar indicates 10 µm.

Fig. 5: Detail from Fig. 3. Nucleus with extraordinary               Fig. 6: Lateral view of a Pyxidicula Pyxidicula showing
structured nucleolus. Scale bar indicates 10 µm.                      the conical (v-shaped) pseudopodia (arrow).
                                                                                           Scale bar indicates 10 µm.

The aperture (the pseudostome, the shell opening) is almost as large as the shell diameter. The shells are shaped like a flattened hemisphere. Fig. 5 shows a rarely observed nucleus figure with the additional zone of aberrant optical density in the center of the nucleolus.

The larger dots in the cell plasma are mitochondria. A piece of chitin from a mosquito that hatched in the sample container and then accidentally fell into the water and died opened up the opportunity to photograph a Pyxidicula cell in lateral vie (Fig. 6). The shell cross section and the aperture are clearly visible. The observer can discover the way of attachment to the substrate and the shape of the pseudopodia.