Environmental Engineering Reference
In-Depth Information
151
(148) (a) Cells circular in outline in one view
but saddle-shaped in another. Striae radi-
ateonvalvesurface.....
Campylodiscus
NB.
It is important to look at a number of
specimens (or turn a single specimen over)
to get the range of views needed to see the
saddle-shaped appearance.
Cells of
Campylodiscus
are quite large
(60-200 μm diameter) and approximately
circular in shape (valve view) or saddle-
shaped (girdle view). One large lobed
chloroplast is present. Widespread in oligo
to eutrophic waters and in brackish and
marine habitats. Epipelic.
Campylodiscus
hibernicus
and
C. noricus
are the most
frequent freshwater species. Bacillario-
phyta. Plate XXIII.
25 μm
(b) Cells not saddle-shaped in any view
..................................
152
152
(151) (a) Cells widely elliptical/oval, one valve
with true raphe, the other with a pseu-
doraphe. Cells isopolar. One C-shaped
chloroplast..................
Cocconeis
Cells of
Cocconeis
are isobilateral and
nearly elliptical in shape. Fine or coarse
striations may be visible on the valve sur-
face running from the raphe/pseudoraphe
tothecellmargin.Theraphe-bearingvalve
slightly concave. Epiphytic and epilithic,
found on rocks and plants, attached by
the concave raphe-bearing valve. Very
widespread and common. Two common
species,
C. pediculus
(11-45 μm long, 9-
30 μm wide) with slightly more rhom-
boid cells and
C. placentula
(10-70 μm
long, 8-35 μm wide). Bacillariophyta.
Plate XXIII. Figs. 2.28, and 4.64.
50 μm
Figure 4.63
Gyrosigma.
A solitary diatom with sig-
moid valves. Top: Live cell, with two elongate chloro-
plasts. Reproduced with permission from G. Ji. Bottom:
Prepared slide, separate species.
NB.
Although
N. sigmoidea
is the most
common of the sigmoid
Nitzschia
species
others do occur, for example,
N. flexa,
,
N.
vermicularis
,
N. acula
,
N. filiformis
and
N. clausii
.
(b) Cells more narrowly elliptical, oval or
elongate. Heteropolar or isopolar. One or
more chloroplasts, not C-shaped . . . .
153
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