A Key to the More Frequently Occurring Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 175

(b) Cells as isolated individuals or form
colonieswhicharenotepiphytic........ 58

58 (57) (a) Cells arranged in a rectilinear series,
often in groups of four, forming a plate
one cell thick, often of many cells
.......................... Merismopedia

Merismopedia cells are spherical to oval
forming a colony of a single layer, shaped as
a plate or rectangle within thin structureless
mucilage. Cells are arranged in rows, some-
times in groups of four. The cells, often a
pale blue in colour, are 0.5-5 μm in diameter
and 1-16 μm long. Free-floating or resting
on bottom sediments. Also occurs in saline
environments. Cyanophyta. Plate IX.

20 μm

(b) Cells not as above but individual or in
spherical, ovate or irregular colonies but 3-
dimensional and not a flat plate . ........ 59

59 (58) (a) Cellsindistinctcolonieswhichformhol-
low spheres with cells arranged regularly
around the periphery . . . ............... 60

50 μm

(b) Cells individual or in colonies that are
not hollow at most clathrate (see Glossary)
with cells distributed throughout . . . . .... 63

Figure 4.30 Gomphosphaeria. Top: Detail from edge
of colony showing pear-shaped, granular cells in side
view (arrow). Bottom: Typical lobed colonies, which
have been slightly compressed to accentuate surface
mucilage and to see peripheral cells. Indian ink prepara-
tion

60 (59) (a) Cells pear-shaped to sub-spherical,
sometimes with a mucilaginous sheath.
Cells arranged at the ends of branching
mucilaginous strands separate from one
another and radiating from the colony centre
........................ Gomphosphaeria

(b) Cells spherical, not pear-shaped, in glob-
ular to spherical colonies.. ............. 61

Gomphosphaeria is widely-dispersed in
lakes, ponds and ditches where it may
become the dominant planktonic alga. Cells
1.5-12 μm wide, 2-16 μm long. Cells
have distinct gelatinised envelopes and
are often arranged in clusters within the
colony. Reported as producing taste and
odour in waters used for drinking (Palmer,
1962). Cyanophyta. Plate IX. Figs. 1.3
and 4.30.

61 (60) (a) Cells not on the end of mucilaginous
stalks within the colony . . Coelosphaerium

Cells of Coelosphaerium are spherical to
sub-spherical or even oval. The cells are
not attached to stalks within the colony,
are closely-packed, and form a more or