A Key to the More Frequently Occurring Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 160

are also present. It can also occur in damp
terrestrial habitats. Chlorophyta. Plate V.

(b) Cells not embedded in a prominent
mucilaginous envelope. ................ 32

32 (31) (a) Filament outline with constrictions giv-
ing it a toothed appearance. ............ 33

(b) Filament outline without constrictions
and does not have toothed appearance . . . 34

100 μm

33 (32) (a) Cells elliptical in shape in one view but
show a deep narrow constriction in alterna-
tive view - giving the filament a toothed
appearance, with the teeth being smoothly
rounded. No gap between adjoining cells.
.......................... Spondylosium

Figure 4.14 Desmidium. Elongate filaments of this
colonial desmid. Inset: Details of four cells, each com-
posed of two semicells.

Spondylosium is a filamentous desmid.
Each cell resembles an angular or rounded
(depending upon the species of Spondy-
losum ) Cosmarium cell with a deep con-
striction - giving the characteristic toothed
appearance to the filament as a whole. Cell
walls fairly smooth. There is one chloro-
plast with pyrenoid in each semicell. Fre-
quent around lake margins in slightly acidic
and oligotrophic upland areas although S.
planum can occur in richer waters. Chloro-
phyta. Plate V.

the vegetation and along the margins of olig-
otrophic lakes. Chlorophyta. Fig. 4.14.

34 (32) (a) Filaments very short, often only 2 or 3
cells long (more like a short chain than a
filament). Cells cylindrical with free ends
rounded . ................... Stichococcus

Stichococcus can occur singly or form very
reduced filaments, just short chains. Cells 1-
16 μm wide and 4-32 μm long. There is
a single-lobed chloroplast but no pyrenoid.
On damp earth, tree trunks etc. as well
as in marine and freshwaters. Chlorophyta.
Plate V.

(b) Cells angular, rarely elliptical, in one
view with a small lens-shaped gap between
the cells usually visible. Cells only have
a small constriction to the toothed margin,
not so pronounced, and the 'teeth' are more
angular . ..................... Desmidium

(b) Filaments many cells in length, not typ-
icallyshort........................... 35

Desmidium is a filamentous desmid. The
cells can form long twisted filaments
enclosed in a gelatinous envelope. When
viewed in transverse section, the filaments
may be triangular. There is one chloroplast
with pyrenoid in each semicell. Cells 26-
50 μm wide. Sometimes the space between
the cells can be difficult to see. Common in

35 (34) (a) Large alga with tubular thallus many
cells wide and long, macroscopic in size
......................... Enteromorpha

Enteromorpha has a tube-like thallus that
may or may not branch and can grow many
centimetres in length. The tube itself con-
sists of a layer one cell thick. The tubes are