Environmental Engineering Reference
In-Depth Information
10 μm
25 μm
Figure 4.66
Encyonema.
Valve view of this asymmet-
ric diatom. Acid digest, lake sediment sample. Repro-
duced with permission from M. Capstick.
Figure 4.67
Rhoicosphenia.
Epiphytic clusters of this
sedentary diatom with cells attached by stalks (arrows).
Fixed preparation.
end to plants and other substrata. Het-
erovalvar with the lower valve having a
fully developed raphe with central nod-
ules and the upper valve with an extremely
reduced raphe in the form of short slits
near the poles (only visible using electron
microscopy). Abundant and widespread in
richer and even brackish waters. Bacillar-
iophyta. Plate XXIV. Figs. 2.29 and 4.67.
(10-260 μm long, 4-50 μm wide) have a
single H-shaped chloroplast with a single
central pyrenoid. Cells can be free-floating
or attached by means of a mucilage pad
to a solid substratum. Can grow in open
water treatment filters and reach large
enough numbers to cause filter-blocking
problems. Bacillariophyta. Plate XXIV.
165
(157) (a) Cells forming star-shaped colonies
..........................
Asterionella
(b) Cellsnotasabove..............
167
167
(166) (a) Cells heteropolar, wedge-shaped in
one view but shaped like an Egyptian
mummy in other view (see Plate XXV)
sometimes many times as long as wide
..................................
168
(see also key No. 78)
(b) Cells not forming star-shaped
colonies..........................
166
166
(165) (a) Cells wedge-shaped and curved along
their apical axis in girdle view, more club-
shaped in valve view. Single H-shaped
chloroplast.............
Rhoicosphenia
(b) Cells not as above, isopolar and not
shaped like an Egyptian mummy . . . .
170
168
(167) (a) Cells narrow, much longer than wide,
tapering slightly to an acute lower pole,
bluntly rounded and slightly capitate
upper pole . . . . ................
Peronia
Cells (12-75 μm long) often attached
by a pad of mucilage at their narrow
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