Page 22 - Algae

General Overview 5

FIGURE 1.1 Transmission electron micrograph of FIGURE 1.2 Ochromonas sp.,
Nannochloropsis sp., non-motile unicell. motile unicell.
(Bar: 0.5 mm.) (Bar: 4 mm.)

(Heterokontophyta) (Figure 1.3) forms long and bushy non-motile colonies with cells evenly dis-
tributed throughout a gelatinous matrix, while Synura (Heterokontophyta) (Figure 1.4) forms free-
swimming colonies composed of cells held together by their elongated posterior ends. When the
number and arrangement of cells are determined at the time of origin and remain and constant
during the life span of the individual colony, colony is termed coenobium. Volvox (Chlorophyta)
(Figure 1.5) with its spherical colonies composed of up to 50,000 cells is an example of motile
coenobium, and Pediastrum (Chlorophyta) (Figure 1.6) with its flat colonies of cells characterized
by spiny protuberances is an example of non-motile coenobium.

FILAMENTOUS ALGAE
Filaments result from cell division in the plane perpendicular to the axis of the filament and have
cell chains consisting of daughter cells connected to each other by their end wall. Filaments can be
simple as in Oscillatoria (Cyanophyta) (Figure 1.7), Spirogyra (Chlorophyta) (Figure 1.8), or
Ulothrix (Chlorophyta) (Figure 1.9), have false branching as in Tolypothrix (Cyanophyta)
(Figure 1.10) or true branching as in Cladophora (Chlorophyta) (Figure 1.11). Filaments of
Stigonema ocellatum (Cyanophyta) (Figure 1.12) consists of a single layer of cells and are
called uniseriate, and those of Stigonema mamillosum (Cyanophyta) (Figure 1.13) made up of
multiple layers are called multiseriate.

SIPHONOUS ALGAE

These algae are characterized by a siphonous or coenocytic construction, consisting of tubular
filaments lacking transverse cell walls. These algae undergo repeated nuclear division without
forming cell walls; hence they are unicellular, but multinucleate (or coenocytic). The sparsely