A Key to the More Frequently Occurring Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 189

(b) Cells without pseudocilia. . . ........ 88

88 (87) (a) Mucilaginous surrounds to the cells
show marked stratification or layering . . . 89

(b) Mucilaginous surrounds to cells more or
less homogenous, no marked stratification
..................................... 90

89 (88) (a) Chloroplast dense and star- shaped
........................... Asterococcus

Cells of Asterococcus are spherical or glob-
ular, up to 40 μm in diameter. A single dense
star-shaped chloroplast with arms radiating
from the centre is present together with a
centrally located pyrenoid. Small groups (1-
16) of cells are surrounded by thick stratified
or lamellate hyaline mucilage. Free-floating,
common in softer shallow waters usually
amongst other algae and moss. Chlorophyta.
Plate XII.

50 μm

Figure 4.46 Sphaerocystis. Free-floating colony of
cells dispersed throughout a globule of mucilage.

(b) Chloroplastcup-shaped,notstar-shaped,
and nearly fills the whole cell . . Gloeocystis other species of algae have palmelloid stages

in their life cycle which gives rise to confu-
sion. The jelly-like masses can cause block-
age of filters in water treatment processes.
Chlorophyta. Plate XII.

Gloeocystis cells (4-23 μm diameter) are
spherical and usually in groups of 4-8-
16 surrounded by stratified or lamellate
mucilage but may also be solitary. There
is a single cup-shaped parietal chloroplast
with pyrenoid and often many starch grains.
Found in more stagnant ponds and ditches
as part of the tychoplankton. Can, if present
in large numbers, impart unwanted odour
to drinking waters (Palmer, 1962). Chloro-
phyta. Plate XII.

(b) Chloroplast parietal with none to many
pyrenoids . . . . .............. Sphaerocystis

Cells 7-20 μm wide, spherical. Colonies
globular and free-floating with cells embed-
ded in stuctureless mucilage. Reproduction
occurs by division of the mother, generating
8-16 daughter cells which form characteris-
tic microcolonies within the parent colony.
Common and sometimes abundant in the
plankton of lakes and also found on damp
soils. Chlorophyta. Plate XII. Fig. 4.46.

90 (88) (a) Chloroplast cup-shaped with a single
pyrenoid ....................... Palmella

Palmella cellsaresphericalorroundedcylin-
ders, 3-15 μm wide, rather like Chlamy-
domonas in the way they are organised. They
are surrounded by an indeinite mucilaginous
mass which may be coloured greenish to red-
dish and are found on damp surfaces. Some

91 (82) (a) Colonies either spherical, oval or a flat
disc.................................. 92

(b) Coloniesnotasabove............ 101