Not all desmids are ornamented. This desmid of the genus Netrium
has a smooth cell wall. But the chloroplasts have complicated bends and
folds.
Desmids are found almost exclusively in fresh water, although there are some species described in brackish water. About 3500 species are known worldwide. Mostly they occur in soft waters, water poor in calcium and magnesium and other dissolved salts.
Often these waters are also a bit acid.
Netrium