From Dumack et al. (2017)

Rhizaspis rugosa  Dumack, Öztoprak, Rüger and Bonkowski, 2017

Diagnosis: Rhizaspis as defined for the genus. The theca comprises lateral and basal folds. Spherical nucleus, with several roundish nucleoli. Cell divided into zones as described for the genus. No floating stages observed. Cysts not observed. In cultures cells may occur basolaterally connected in a ring, built through unfinished fission, not fusion. Easy to confuse with Rhizaspis scutiformis or Rhizaspis granulata which have different nucleoli.

Dimensions: The cell bodies were oval and flattened with a length of 57.51 ± 2.65 µm, a width of 40.79 ± 6.33 µm and a length-width ratio of 1.44 ± 0.22 (n = 10). Several zones characterized the cell body: The nucleus (12.62 ± 1.45 µm, n = 10) was located at the apical end of the cell, embedded by numerous granules (1.27 ± 0.41 µm; n = 30). It contained a varying amount of nucleoli (3.32 ± 1.16 µm).

Type locality: quarry pond next to river Rhine, in Xanten, Germany (51.691441, 6.425774).

Remarks: Dumack et al 2017: “A layer of food vacuoles separated this area from several (difficult to detect) contractile vacuoles close to the aperture.The cell body was covered by a hyaline, flexible(i.e. stretchable) theca that was most often carried in an upright position sometimes drawn after. It exhibited two lateral folds on each side that might have only be seen if cells are starving or compressed between glass slides. Additionally, smaller randomly dispersed folds could be observed. The aperture itself usually was slit-like, but showed high flexibility, as it sometimes stretched to different polygon- or almost round shapes. The cells crept by filopodia, which originated from the aperture or at a plate of cell plasma that by itself originated from the aperture. The filopodia branched and anastomosed with a maximum measured length of 110  µm. They lacked granules; instead stripes (cytoskeletal filaments) were prominent. Motile cells usually expanded most filopodia in the direction of movement, non-moving cells formed filopodia in all directions. No floating or flagellated cell stages were observed. Division was longitudinal.”

From Kootwijk, Netherlands, 2018
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