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- Cosmarium is
a single-celled placoderm desmid. The cells are deeply divided
in the middle by a short isthmus that contains the nucleus. The
two semicells are rounded in front view and flattened, oval,
or elliptic in side view. The older half of the cell wall secretes
mucilage, while the younger half
- is lifted off of the substrate at a slight
angle. The mucilage swells as it absorbs water and propels
- the cell forward. The cell wall may be smooth
with pores or ornamented with granules, pits, or warts. The vegetative
cells usually do not have spines. Each semicell has at least
one central chloroplast (usually 2 or 4) with pyrenoids. Cosmarium
sometimes produces thick-walled resting cells.
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- Triradiate cells with three semicells have
sometimes grown in collections or cultures.
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- This cell is empty,
with only the
- protective cell wall
remaining.
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