30
Algae
higher numbers of microtubules, according to the formula X-2-X-2. When viewed from above the
cell, the basal bodies and rootlets can have a perfect cruciate pattern, with the basal bodies directly
opposed (DO) or they can be offset in a clockwise (CW) or counterclockwise (CCW) position.
According to the most recent classifications, Chlorophyta comprises the early-diverging prasinophytes, which gave rise to the core chlorophytes (including the early diverging Chloredendrophycae
with the three major classes of Ulvophyceae, Trebouxiophyceae, and Chlorophyceae), to the
Pedinophyceae, sister class to the core chlorophytes, and the recently proposed group Palmophyllales.
The prasinophytes, as presently conceived, include a heterogeneous assemblage of unicellular
motile algae, either naked or covered on their cell body and flagella by nonmineralized organic
scales (Figures 1.1l and 1.39). They are predominantly marine planktonic, but also include several
freshwater representatives. At present, nine prasinophyte clades are recognized, two of which have
been recently accommodated into the two classes of Mamiellophyceae and Nephroselmidophyceae.
Mamiellophyceae (Figure 1.1m) are typically solitary cells, with one or two chloroplasts,
mono- or biflagellate, with isokont or anisokont flagella. They may be scale-covered or naked.
Nephroselmidophyceae (Figure 1.1n) are laterally compressed, scale-covered cells, with laterally
inserted anisokont flagella, and possess a single cup-shaped chloroplast. Pedinophyceae (Figure
1.1o) are unicellular, monoflagellate asymmetrical algae, with CCW basal body orientation. Rigid or
thin hair-like appendages are present on the flagellum. Chloredendrophyceae (Figure 1.1p) possess a
pair of flagella inserted in a pit; basal body orientation is CCW. These algae are covered by organic
scales, the outer layer of which is fused to form a theca. The class Chlorophyceae (Figure 1.1q)
comprises mainly swimming cells with one or two pair of flagella, without mastigonemes. Cells can
be naked or covered by a cell wall more or less calcified (Figure 1.40). Either DO or CW arrangements are present in the members of this class. Ulvophyceae morphologies range from microscopic
unicellular to macroscopic multicellular plants and giant-celled organisms (Figures 1.1r, 1.41, and
1.42). Four main cytomorphological types can be distinguished: nonmotile uninucleate unicells;
multicellular filaments or blades composed of multinucleate cells; multicellular bodies composed
of multinucleate cells with nuclei organized in regularly spaced cytoplasmic domains; siphonous
thalli consisting of a single giant tubular cell containing thousands to millions of nuclei. In some
species, siphonous thalli are encrusted with calcium carbonate. The majority of Ulvophyceae are
marine, but several members also occur in freshwater or damp subaerial habitats. All the algae of
FIGURE 1.39 Unicell of Pyramimonas longicauda.
Algae
higher numbers of microtubules, according to the formula X-2-X-2. When viewed from above the
cell, the basal bodies and rootlets can have a perfect cruciate pattern, with the basal bodies directly
opposed (DO) or they can be offset in a clockwise (CW) or counterclockwise (CCW) position.
According to the most recent classifications, Chlorophyta comprises the early-diverging prasinophytes, which gave rise to the core chlorophytes (including the early diverging Chloredendrophycae
with the three major classes of Ulvophyceae, Trebouxiophyceae, and Chlorophyceae), to the
Pedinophyceae, sister class to the core chlorophytes, and the recently proposed group Palmophyllales.
The prasinophytes, as presently conceived, include a heterogeneous assemblage of unicellular
motile algae, either naked or covered on their cell body and flagella by nonmineralized organic
scales (Figures 1.1l and 1.39). They are predominantly marine planktonic, but also include several
freshwater representatives. At present, nine prasinophyte clades are recognized, two of which have
been recently accommodated into the two classes of Mamiellophyceae and Nephroselmidophyceae.
Mamiellophyceae (Figure 1.1m) are typically solitary cells, with one or two chloroplasts,
mono- or biflagellate, with isokont or anisokont flagella. They may be scale-covered or naked.
Nephroselmidophyceae (Figure 1.1n) are laterally compressed, scale-covered cells, with laterally
inserted anisokont flagella, and possess a single cup-shaped chloroplast. Pedinophyceae (Figure
1.1o) are unicellular, monoflagellate asymmetrical algae, with CCW basal body orientation. Rigid or
thin hair-like appendages are present on the flagellum. Chloredendrophyceae (Figure 1.1p) possess a
pair of flagella inserted in a pit; basal body orientation is CCW. These algae are covered by organic
scales, the outer layer of which is fused to form a theca. The class Chlorophyceae (Figure 1.1q)
comprises mainly swimming cells with one or two pair of flagella, without mastigonemes. Cells can
be naked or covered by a cell wall more or less calcified (Figure 1.40). Either DO or CW arrangements are present in the members of this class. Ulvophyceae morphologies range from microscopic
unicellular to macroscopic multicellular plants and giant-celled organisms (Figures 1.1r, 1.41, and
1.42). Four main cytomorphological types can be distinguished: nonmotile uninucleate unicells;
multicellular filaments or blades composed of multinucleate cells; multicellular bodies composed
of multinucleate cells with nuclei organized in regularly spaced cytoplasmic domains; siphonous
thalli consisting of a single giant tubular cell containing thousands to millions of nuclei. In some
species, siphonous thalli are encrusted with calcium carbonate. The majority of Ulvophyceae are
marine, but several members also occur in freshwater or damp subaerial habitats. All the algae of
FIGURE 1.39 Unicell of Pyramimonas longicauda.