A Key to the More Frequently Occurring Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 156

ls

ss

10 μm

10 μm

Figure 4.10 Fragilaria . Top: Ribbon arrangement of
diatom colony. Fixed sample. Bottom: Single cell show-
ing fine transverse striae, with central clear area (arrow).
Acid digest, lake sediment sample. Reproduced with per-
mission from M. Capstick.

40-170 μm long, 2-4 μm wide. Fragilaria
capucina is also widespread occurring in
lakesandrivers,10-100μmlong,3.5-4.5μm
wide. Can impart unwanted odour to drink-
ing waters (Palmer, 1962). Large numbers
can cause filter-clogging problems in water
treatment works. Bacillariophyta. Plate IV.
Fig. 4.10.

10 μm

29 (28) (a) Cells rectangular or tabular in normal
view, sometimes united to form zig-zag
colonies. When seen individually and not
as part of a chain the valves often show a
strongly swollen middle region. Cells with-
out costae but have internal septa which can
be clearly seen.. ............... Tabellaria

Figure 4.9 Aulacoseira granulata . Cells have termi-
nal long (ls) and short (ss) spines.