Environmental Engineering Reference
In-Depth Information
Tabellaria
cells are rectangular in girdle
view, forming colonies that may be stellate
or zig-zag. The stellate colonies can be con-
fused with
Asterionella
but can be told apart
by (1) internal septa in
Tabellaria
and (2)
more squared-off ends to the cells in
Tabel-
laria
when compared with the more rounded
ends in
Asterionella
.
Tabellaria fenestrata
(33-116 μm long, 4-10 μm wide) andT.
T.loc-
culosa
(6-130 μm long,
<
5 μm wide) are the
most frequent species.
Common in the plankton of less nutrient-rich
lakes although they can be seen in mildly
eutrophic conditions. Different species have
been reported to prefer either mildly acid
or slightly alkaline conditions (Wehr and
Sheath, 2003). Large numbers can clog water
treatment filters. Bacillariophyta. Plate IV.
Figs. 2.28 and 4.11.
25 μm
(b) Cells rectangular, may unite to form zig-
zag colonies. Cells rod-shaped when seen
individually with at the most slightly swollen
centres. Transverse costae present within the
cells............................
Diatoma
Diatoma
forms zig-zag or ribbon-like
colonies or chains. Internal costaearepresent
and these may be seen as ridges or points
at the cell margin. Chloroplasts discoid to
plate-like,
10 μm
10 per cell. Cells may be capi-
tate. Several species occur - the more com-
mon of which are
D. vulgaris
with cells
(8-75 μm long and 7-18 μm wide) hav-
ing bluntly rounded ends, common in the
plankton of moderately eutrophic lakes and
rivers and
D. tenuis
(22-120 μm long,
>
Figure 4.11
Tabellaria
. Top: Zig-zag colony from river
biofilm. Fixed preparation. Bottom: Different species -
valve view of single cell. Reproduced with permission
from M. Capstick. Acid digest, lake sediments.
>
10
m wide) with capitate apices wider than
the rest of the cell. Planktonic and epi-
phytic. Large numbers of planktonic species
can cause filter-clogging problems in water
treatment works. Bacillariophyta. Plate V.
Fig. 4.12.
Spirogyra
hascylindricalcellsthatarejoined
end to end to form an unbranched fila-
ment. Cell walls are firm, with a thin film
of mucilage on the outside - often giving
them a slimy feel. Chloroplasts (up to 15 per
cell) have a helical shape and possess numer-
ous pyrenoids. The various forms of spiral
chloroplast in different species are shown in
Plate V. The nucleus, often visible in live
30
(24) (a) Chloroplasts form a distinct spiral band
withinthecell.................
Spirogyra
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