Environmental Engineering Reference
In-Depth Information
Cells (3-6 μm wide, 15-25 μm long) have
a single chloroplast (sometimes two) which
is parietal and may or may not have one
or two pyrenoids. Cells of Elakatothrix
have a characteristic spindle or fusiform
shape (tapering to a point at both ends)
and are arranged in pairs or somewhat
irregularly within mucilaginous colonies.
Usually free-floating, an occasional plank-
tonic species especially in more nutrient-rich
waters. Chlorophyta. Plate XI.
85 (83) (a) Cells spherical, ovoid or ellipsoidal and
more or less radially arranged at the ends
of strands of mucilage, and embedded in
mucilage, to form a radiating globular colony
........................ Dictyosphaerium
20 μm
Dictyosphaerium coenobia are composed of
4 to 64 cells which are spherical to sub-
reniform and are connected by threads radi-
ating from the colony centre. The whole is
embedded in mucilage. Cells spherical to
ovoid, 3-10 μm in diameter, with parietal
cup-shaped chloroplasts with pyrenoids. Fre-
quent in the plankton of lakes and ponds
and slow moving waters. Can be found
amongst submerged macrophytes or sub-
merged objects. May impart an odour to
drinking waters (Palmer, 1962). Chloro-
phyta. Plate XI. Fig. 4.45.
Figure 4.45 Dictyosphaerium. Phase contrast image
of single colony. Cells are attached to fine mucilaginous
threadsradiatingoutfromthecentreofthecolony.Repro-
duced with permission from R. Matthews.
10 μm long), are embedded in a tough oily
mucilage. The chloroplast is parietal with a
pyrenoid. Widespread in the plankton but not
usually abundant. Chlorophyta. Plate XI.
(b) Cells of colony not so densely packed
andcoloniesnotbrownincolour....... 87
(b) Cells not attached to mucilage strands
that are radially arranged. .............. 86
87 (86) (a) Cells with pseudocilia (see Glossary)
.............................. Tetraspora
86 (85) (a) Cellofcolonyverydenselypacked,often
appearing dark brown to black in colour.
Individual cells can be difficult to disting-
uish....................... Botryococcus
Tetraspora forms large irregular gelatinous,
often balloon-like, colonies that can be vis-
ible to the naked eye. The cells (6-12 μm
diameter) are in groups of 2 or 4 within
the mucilage. Each cell usually has two fine
pseudocilia and they are arranged around
the edge of the colony and may extend
beyond the mucilage. The chloroplast is cup-
shaped and a pyrenoid is present. Common
in the plankton of shallow waters, ponds and
ditches or associated with submerged macro-
phytes. Chlorophyta. Plate XI.
Cells of Botryococcus , difficult to see
because they are so densely packed, may
be visualised by gently squashing the
colony under the microscope cover slip. The
colonies may be pale but are often quite dark
and look like a piece of organic debris. Cells,
roughly spherical in shape (3-9 μm wide, 6-
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