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Anatomy
In eukaryotic algae, mucilages and sheaths are present in diverse divisions. The most common occurrence of this extracellular material is in the algae palmelloid phases, in which nonmotile cells are embedded in a thick, more or less stratified, sheath of mucilage. This phase
is so called because it occurs in the genus Palmella (Chlorophyceae), but it is also present in
other members of the same class, such as Asterococcus sp., Hormotila sp., and Gloeocystis
sp. A palmelloid phase is also present in Spirogyra sp. (Zygnematophyceae), Chroomonas sp.
(Cryptophyceae), Gloeodinium montanum vegetative cells (Dinophyceae) Euglena gracilis
(Euglenophyceae) (Figure 1.22). Less common are the cases in which filaments are covered
by continuous tubular layers of mucilages and sheath. It occurs in the filaments of Geminella
sp. (Trebouxiophyceae). A more specific covering exists in the filaments of Phaeothamnion
sp. (Phaeothamniophyceae), since under certain growth conditions, cells of the filaments dissociate and produce a thick mucilage that surround them in a sort of colony resembling the
palmelloid phase.
Scales
Scales can be defined as organic or inorganic surface structures of distinct size and shape. Scales
can be distributed individually or arranged in a pattern sometimes forming an envelope around
the cell. They occur only in eukaryotic algae, in the divisions of Ochrophyta, Haptophyta, and
Chlorophyta. They can be as large as the scales of Haptophyta (1 μm), but also as small as the scales
of Prasynophytes (Chlorophyta) (50 nm). There are at least three distinct types of scales: nonmineralized scales, made up entirely of organic matter, primarily polysaccharides, which are present
in the Prasynophytes (Chlorophyta); scales consisting of calcium carbonate crystallized onto an
organic matrix, as the coccoliths produced by many Haptophyta; and scales constructed of silica
deposited on a glycoprotein matrix, formed by some members of the Ochrophyta.
FIGURE 2.2 TEM image of the apical cell of Leptolyngbya spp. trichome in longitudinal section. The
arrows point to the mucilaginous sheath of this cyanobacterium. Inside the cell, osmiophylic eyespot globules
are present. Scale bar, 0.15 μm. (Courtesy of Prof. Patrizia Albertano.)
Anatomy
In eukaryotic algae, mucilages and sheaths are present in diverse divisions. The most common occurrence of this extracellular material is in the algae palmelloid phases, in which nonmotile cells are embedded in a thick, more or less stratified, sheath of mucilage. This phase
is so called because it occurs in the genus Palmella (Chlorophyceae), but it is also present in
other members of the same class, such as Asterococcus sp., Hormotila sp., and Gloeocystis
sp. A palmelloid phase is also present in Spirogyra sp. (Zygnematophyceae), Chroomonas sp.
(Cryptophyceae), Gloeodinium montanum vegetative cells (Dinophyceae) Euglena gracilis
(Euglenophyceae) (Figure 1.22). Less common are the cases in which filaments are covered
by continuous tubular layers of mucilages and sheath. It occurs in the filaments of Geminella
sp. (Trebouxiophyceae). A more specific covering exists in the filaments of Phaeothamnion
sp. (Phaeothamniophyceae), since under certain growth conditions, cells of the filaments dissociate and produce a thick mucilage that surround them in a sort of colony resembling the
palmelloid phase.
Scales
Scales can be defined as organic or inorganic surface structures of distinct size and shape. Scales
can be distributed individually or arranged in a pattern sometimes forming an envelope around
the cell. They occur only in eukaryotic algae, in the divisions of Ochrophyta, Haptophyta, and
Chlorophyta. They can be as large as the scales of Haptophyta (1 μm), but also as small as the scales
of Prasynophytes (Chlorophyta) (50 nm). There are at least three distinct types of scales: nonmineralized scales, made up entirely of organic matter, primarily polysaccharides, which are present
in the Prasynophytes (Chlorophyta); scales consisting of calcium carbonate crystallized onto an
organic matrix, as the coccoliths produced by many Haptophyta; and scales constructed of silica
deposited on a glycoprotein matrix, formed by some members of the Ochrophyta.
FIGURE 2.2 TEM image of the apical cell of Leptolyngbya spp. trichome in longitudinal section. The
arrows point to the mucilaginous sheath of this cyanobacterium. Inside the cell, osmiophylic eyespot globules
are present. Scale bar, 0.15 μm. (Courtesy of Prof. Patrizia Albertano.)