Environmental Engineering Reference
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waters often poor in nutrients and acidic.
Bacillariophyta. Plate XXIII.
Cells of
Reimeria
are dorsiventral in shape
(see Glossary) with rounded (slightly
rostrate) apices, and have an obvious
swollen area in the centre of the con-
cave margin. Cells (9-40 μm long, 3-9 μm
wide) contain a single-lobed chloroplast.
Widespread on damp rocks, in mosses and
in rivers. Bacillariophyta. Plate XXIII.
(b) Cellsnotasabove..............
162
162
(161) (a) Cells crescent-shaped with a straight
ventral surface in valve view, oval in girdle
view, with squared-off apices. Cell apices
rounded, hyaline area between markings
on central dorsal surface in some species
.............................
Amphora
164
(162) (a) Cells with strongly curved dorsal
surface and a slightly convex, straight
or slightly inflated ventral surface (see
Plate XXIV). Central ends of raphe bent
upwards (towards dorsal surface) and
polar ends bent downwards (towards the
ventral surface) . ...........
Encyonema
Amphora
cells usually lie so that they are
seeningirdleview.Thevalvesarestrongly
arched so that each raphe, which is curved,
appears on the same side. There is an H-
shaped chloroplast. Cells (30-90 μm long,
20-40 μm wide) broadly oval in girdle
view with rounded apices.
Amphora
is a
benthic diatom, primarily marine but also
widespread in freshwaters. Perhaps more
common in harder richer waters. Often
found as an epiphyte and usually with its
concave face against the substrate. Bacil-
lariophyta. Plate XXIV.
Valves strongly arched on the dorsal mar-
gin and nearly straight on the ventral mar-
gin giving them the appearance of an
orange segment (see also
Cymbella
). The
raphe is closer to the ventral margin and
approximately parallel to it. Frustule sur-
face with very fine striae not easily seen
with a light microscope. Cells (20-58 μm
long, 3-30 μm wide) contain an H-shaped
chloroplast with a pyrenoid and are soli-
tary or enclosed in a mucilage tube. A
widespread genus in rivers on rocks and
other substrata. In older texts this genus in
usually included with
Cymbella.
Bacillar-
iophyta. Plate XXIV. Fig. 4.66.
(b) Cells not shaped as above and without
hyaline area between markings on dorsal
surface...........................
164
163
(160) (a) Cells with no true raphe. Up to 150 μm
long, 4-8 μmwide............
Hannaea
Cells curved (banana-shaped) with a con-
cave ventral surface that has a swollen
area in its centre. Cells (5-150 μm long,
2-50 μm wide) with slightly capitate
or rostrate ends, containing two lobed
chloroplasts (only one of which may be
visible). Either solitary or in small groups
on stones and rocks. Single common
species,
H. arcus
. Found in cooler upland
streams, sometimes slightly acidic and
in larger lake margins. Bacillariophyta.
Plate XXIII.
(b) Cells with gently curved dorsal sur-
face. Central raphe ends bent downwards
(towards the ventral surface) and polar
ends bent upwards (towards the dorsal sur-
face) ........................
Cymbella
Cymbella
cells have a convex dorsal mar-
gin and a straight, concave or slightly con-
vex ventral margin. Valve surface with
striae at right angles to the raphe, which is
usually central with the outer ends turned
upwards and the central ends turned down-
wards towards the ventral margin. Cells
(b) Cells with a true raphe (9-40 μm long,
3-9 μmwide)................
Reimeria
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