Environmental Engineering Reference
In-Depth Information
True Navicula species have lanceolate
valves with a narrow axial area flanked
by fine striae which are slightly radiate
at the centre but parallel towards the cell
apices. The raphe is hooked at the apices
with the ends both pointing the same way.
Cells are often very motile with a glid-
ing motion (naviculoid movement). Cell
apices may be narrowly rounded or sub-
capitate. Two plate-like chloroplasts are
usually present lying either side of the api-
cal axis - though some species, N. sub-
tilissima and N. bryophilia , have a sin-
gle, almost H-shaped, chloroplast. A very
widespread and common genus. Found in
a range of waters often occurring in ben-
thic films in streams and rivers as well as
in lakes. Bacillariophyta. Figs. 4.73a and
4.73b.
A
5 μm
10 μm
B
202 (201) (a) Raphe short with thickened
ridges, only visible towards the poles
......................... Amphipleura
C
Amphipleura can be widespread but is not
very common. The valves are lanceolate
and the raphe is very short and located
near to each pole edged by a definite rib.
Cells(80-140μmlong,7-9μmwide)con-
tain a single H-shaped chloroplast with
pyrenoid. Found on silt and sediments,
sometimes mixed with filamentous algae.
More often reported from alkaline waters.
Bacillariophyta. Plate XXVII.
20 μm
(b) The thickened area either side of the
raphe extends along the whole length of
thevalve.......................... 203
Figure 4.72 (A) Golenkinia ,(B) Lagerheimia, (C)
Micractinium .
203 (202) (a) Cells ovoid, two distinctly lobed
chloroplasts, one either side of the long
axis........................ Diploneis
of striae on the valve surface. Cells 10-
130 μm long, 10-60 μm wide. Found on
bottom deposits and silt in a wide range of
waters. Bacillariophyta. Plate XXVII.
Diploneis cellsarelinear,rhombicorellip-
tical. The poles are blunt and rounded. The
raphe is along the mid-line and bordered
by two ridges. There are different types
(b) Cells more elongate. Chloroplast not
lobed. . . ..................... Frustulia
 
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