A Key to the More Frequently Occurring Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 177

less single layer towards the outside of the
colony. Colonies are blue-green in colour
and are common in the plankton sometimes
reaching bloom proportions. Cells 2-5 μm
wide, 2-7 μm long. Gas vacuoles may be
present. This genus can potentially produce
taste and odours in drinking waters. Colonies
20-180 μm in diameter. Cyanophyta.
Plate IX.

(b) Cells with stalks (sometimes not very
distinct) radiating from the centre of the
colony............................... 62

62 (61) (a) Cells spherical to slightly elongated.
Arranged at the ends of thin branched stalks
whicharequiteeasilyseen....... Snowella

5 μm

Figure 4.31 Synechocystis . Group of loosely associ-
ated cells from plankton sample. Reproduced with per-
mission from G. Ji.

Cells forming a free-floating globular colony
embedded in mucilage. The cells are located
towards the outside of the colony but do
not form a single distinct layer and are
located at the ends of distinct branched
stalks. Cells 1.5-3.0 μm in diameter, 2-4 μm
long. Gas vacuoles uncommon. Colonies up
to 80 μm in size. Widespread in the plankton
of eutrophic standing waters. Cyanophyta.
Plate IX.

(b) Mucilaginous colonies composed of
many cells, often in the hundreds ....... 66

64 (63) (a) Cells spherical or slightly oval . ..... 65

(b) Cells elongate, that is, longer than wide,
sometimescylindrical..... Synechococcus

(b) Cells spherical to obovoid, stalks indis-
tinctbutquitethicknearcolonycentre.Stalks
branched, with cell at the end of the some-
times numerous branches. . . . Woronichinia

Synechococcus cells areovoidtocylindrical,
1-12 μm wide, 2-10 times as long as wide.
Cells either solitary or in twos or rarely fours,
sometimes in short chains. Mucilage enve-
lope either thin or absent. Frequent in fresh-
water plankton and on damp surfaces. Also
in brackish waters. Cyanophyta. Plate IX.
Fig. 4.31 shows Synechocystis , a closely
related genus.

Woronichinia cells are arranged in the outer
region of the colony which may contain sev-
eral hundred cells. Cells (3.5-5.0 μmdiam-
eter, 5-7 μm long) are embedded in fine
mucilage. Colonies are free-floating and up
to 180μm in diameter. Common in the plank-
ton of standing waters. Can be difficult to dis-
tinguish from Coelosphaerium. Cyanophyta.
Plate IX.

65 (64) (a) Cells with a distinct envelope of
mucilagewhichislamellateandusuallythick
............................ Gloeocapsa

63 (59) (a) Cells solitary or forming small colonies
of 2-4-8 (rarely 16-32) cells, sometimes but
not always embedded in mucilage. . ..... 64

Gloeocapsa cells are spherical (1-17 μm
diameter) and are surrounded by a sheath