Algae World: Sellaphora

Sellaphora bacillum (interference contrast optics)

On loading, this page will display a series of photographs showing progressively deeper levels within a single interphase cell of Sellaphora bacillum, from the epivalve to the hypovalve (Firefox handles this better than Internet Explorer). Clicking on the image will give an enlarged version (which opens in a new window: you may need to wait for a short time) as an interactive focusable stack.

The series of images can also be viewed as a video (.avi file) [we strongly recommend that you use QuickTime for this, because it will allow you to select individual frames or move backwards or forwards through the sequence] 

This cell is shown in 'valve view', i.e. with the valves in face view, perpendicular to the line of sight. A similar cell is presented in 'girdle view' on the next page.

What can be seen?

• The epivalve (first frame) displays the characteristic morphology of S. bacillum, with slightly radial striae, a slightly expanded, rounded central area, and grooves on either side of the raphe system.
• Just beneath the valves, in the thin peripheral layer of cytoplasm, are many elongate strands, which are probably mitochondria.
• The chloroplast is H-shaped, comprising two large plates lying against the girdle, which are connected by a wide bridge lying beneath the epivalve.
• There is a ± tetrahedral pyrenoid embedded in the chloroplast.
• The pyrenoid is penetrated by narrow tube-like channels, which extend out from a larger invagination along the interior edge of the tetrahedron.
• The nucleus lies on one side of the cell at the centre, opposite the pyrenoid, and is surrounded by a single layer of dictyosomes (Golgi bodies), which appear in section as short lines. The nucleus contains a single spherical nucleolus.
• Connecting the nucleus and pyrenoid is a bridge of cytoplasm. On each side of the bridge is a large vacuole (the 'empty spaces' between centre and poles).
• Near the hypovalve there are two 'volutin granules', one in each vacuole; these were moving around as the image stack was created..
• On the outside of the cell, you can see many bacteria and a small yellow-green alga containing a red eyespot.