8
Algae
Unicells and Unicell colonial Type
Many algae are solitary cells, the unicell, with or without flagella, hence motile or nonmotile.
Nannochloropsis (Ochrophyta) (Figures 1.1am and 1.2) is an example of a nonmotile unicell, while
Ochromonas (Ochrophyta) (Figures 1.1ai and 1.3) is an example of a motile unicell. Other algae
exist as aggregates of few or many single cells held together loosely or in a highly organized fashion, the colony. In this type of aggregate, cell number is indefinite, growth occurs by cell division
of its components, there is no division of labor, and each cell can survive on its own. Hydrurus
(Ochrophyta) (Figure 1.4) forms long and bushy nonmotile colonies with cells evenly distributed
throughout a gelatinous matrix, while Synura (Ochrophyta) (Figures 1.1bd and 1.5) forms freeswimming colonies composed of cells held together by their elongated posterior ends. Another
quite unusual example of colony is Tetraflagellochloris mauritanica (Chlorophyta) (Figure 1.6a and
1.6b): up to 12 cells can be arranged in groups, which are connected by intercellular diaphragms
and cytoplasmic bridges, without sharing any common colonial boundary. When the number and
arrangement of cells are determined at the time of origin of the colony and remain constant during
FIGURE 1.2 Transmission electron micrograph of a Nannochloropsis sp. nonmotile unicell. Scale bar:
0.5 μm.
FIGURE 1.3 Ochromonas sp. motile unicell. Scale bar: 4 μm.
Algae
Unicells and Unicell colonial Type
Many algae are solitary cells, the unicell, with or without flagella, hence motile or nonmotile.
Nannochloropsis (Ochrophyta) (Figures 1.1am and 1.2) is an example of a nonmotile unicell, while
Ochromonas (Ochrophyta) (Figures 1.1ai and 1.3) is an example of a motile unicell. Other algae
exist as aggregates of few or many single cells held together loosely or in a highly organized fashion, the colony. In this type of aggregate, cell number is indefinite, growth occurs by cell division
of its components, there is no division of labor, and each cell can survive on its own. Hydrurus
(Ochrophyta) (Figure 1.4) forms long and bushy nonmotile colonies with cells evenly distributed
throughout a gelatinous matrix, while Synura (Ochrophyta) (Figures 1.1bd and 1.5) forms freeswimming colonies composed of cells held together by their elongated posterior ends. Another
quite unusual example of colony is Tetraflagellochloris mauritanica (Chlorophyta) (Figure 1.6a and
1.6b): up to 12 cells can be arranged in groups, which are connected by intercellular diaphragms
and cytoplasmic bridges, without sharing any common colonial boundary. When the number and
arrangement of cells are determined at the time of origin of the colony and remain constant during
FIGURE 1.2 Transmission electron micrograph of a Nannochloropsis sp. nonmotile unicell. Scale bar:
0.5 μm.
FIGURE 1.3 Ochromonas sp. motile unicell. Scale bar: 4 μm.