39
General Overview
(20:5, n-3); this peculiarity is the basis for the choice of the Latin noun pingue (adj. fat) as the root for
the class name. Placidiophyceae are kidney-shaped unicell with two flagella arising from a subapical
region of the flattened ventral side. Cells that are usually attached to the substratum can glide or swim
freely. They ingest prey particles on the posterior ventral side (Figure 1.1ba). Phaeothanmniophyceae
can be filamentous (Figure 1.1bb), palmelloid, or coccoid; the vegetative cells are surrounded by a
distinct cell wall of varying thickness. During cell division, an entirely new cell wall is formed inside
the parent cell wall, that is, the new walls are formed by eleutheroschisis. Swimming stages have
flagella inserted laterally. Synchromophyceae cell types can be sessile, migrating, and floating amoebae, surrounded by a lorica usually with one ostiole, through which reticulopodia protrude and fuse
with neighboring cell to build up a meroplasmodium (Figure 1.1bc). The most striking and unique
morphological feature of these algae is the aggregation of chloroplasts, each with two membranes,
into groups of up to eight enclosed in a common periplastidial membrane and epiplastid rough ER.
Synurophyceae are unicellular and colonial algae, important components of the species composition
and biomass in freshwater environment worldwide (Figures 1.1bd and 1.5). A well-organized cell
covering of siliceous, overlapping scales is characteristic of the class. These scales are morphologically unique for each species, and observations made with electron microscopy usually are required
for species-level identification. They differ from closely related Chrysophyceae in the presence of
only chlorophyll c 1 , the parallel basal body orientation and the lack of eyespot. Aurearenophyceae
(Figure 1.1be), a recently established class, are nonmotile algae, surrounded by a cell wall, with two
unequal flagella lying inside the cell wall, or cells naked, motile, and biflagellate.
cercozoa—chlorarachniophyceae
Chlorarachniphyceae are naked, uninucleate cells that form a net-like plasmodium via filopodia (Figures
1.1bf, 1.53a, and 1.53b). The basic life cycle of these algae comprises ameboid, coccoid, and flagellate
cell stages. The ovoid zoospores bear a single flagellum that during the swimming wraps around the
cell. Chlorachniophytes are marine. They possess chlorophyll a and b. Each chloroplast has a prominent projecting pyrenoid and is surrounded by four envelope membranes. Thylakoids are grouped in
stacks of 1–3. A nucleomorph is present between the second and third membranes of the chloroplast
envelope. The origin of this organelle is different from the origin of the cryptophyte nucleomorph, since
the chlorachniophytes came from a green algal endosymbiont. Paramylon (β-1,3-glucan) is the storage
carbohydrate. They can phototrophic and phagotrophic, engulfing bacteria, flagellates, and eukaryotic
algae. Asexual reproduction is carried out by either normal mitotic cell division or zoospore formation.
Sexual reproduction characterized by heterogamy has been reported for only two species.
myzozoa—dinophyceae
Dinophyceae are typical unicellular flagellates, but can be also nonflagellate, ameboid, coccoid,
palmelloid, or filamentous (Figures 1.1bg, 1.1bh, 1.54, and 1.55). Dinoflagellates have two flagella
with independent beating pattern, one training, one girdling that confer characteristic rotatory
swimming whirling motion. Flagella can be apically inserted (desmokont-type) or emerging from
a region close to the midpoint of the ventral side of the cell (dinokont-type). Most dinoflagellates
are characterized by cell-covering components that lie beneath the cell membrane. Around the cell,
there is a superficial layer of flat, polygonal vesicles, which can be empty or filled with cellulose
plates. In dinokont-type dinoflagellates, these thecal plates generally form a bipartite armor, consisting of an upper, anterior half and a lower, posterior half, separated by a groove known as cingulum,
where the transversal flagellum is located (Figure 1.55). A smaller groove, the sulcus, extends posteriorly from the cingulum and hosts the longitudinal flagellum. The two flagella emerge from a pore
located at the intersection of the two grooves. Very often dinoflagellates are important components
of the microplankton of freshwater and marine habitats. Though most are too large (2–2000 μm) to
be consumed by filter feeders, they are readily eaten by larger protozoa, rotifer, and planktivorous
General Overview
(20:5, n-3); this peculiarity is the basis for the choice of the Latin noun pingue (adj. fat) as the root for
the class name. Placidiophyceae are kidney-shaped unicell with two flagella arising from a subapical
region of the flattened ventral side. Cells that are usually attached to the substratum can glide or swim
freely. They ingest prey particles on the posterior ventral side (Figure 1.1ba). Phaeothanmniophyceae
can be filamentous (Figure 1.1bb), palmelloid, or coccoid; the vegetative cells are surrounded by a
distinct cell wall of varying thickness. During cell division, an entirely new cell wall is formed inside
the parent cell wall, that is, the new walls are formed by eleutheroschisis. Swimming stages have
flagella inserted laterally. Synchromophyceae cell types can be sessile, migrating, and floating amoebae, surrounded by a lorica usually with one ostiole, through which reticulopodia protrude and fuse
with neighboring cell to build up a meroplasmodium (Figure 1.1bc). The most striking and unique
morphological feature of these algae is the aggregation of chloroplasts, each with two membranes,
into groups of up to eight enclosed in a common periplastidial membrane and epiplastid rough ER.
Synurophyceae are unicellular and colonial algae, important components of the species composition
and biomass in freshwater environment worldwide (Figures 1.1bd and 1.5). A well-organized cell
covering of siliceous, overlapping scales is characteristic of the class. These scales are morphologically unique for each species, and observations made with electron microscopy usually are required
for species-level identification. They differ from closely related Chrysophyceae in the presence of
only chlorophyll c 1 , the parallel basal body orientation and the lack of eyespot. Aurearenophyceae
(Figure 1.1be), a recently established class, are nonmotile algae, surrounded by a cell wall, with two
unequal flagella lying inside the cell wall, or cells naked, motile, and biflagellate.
cercozoa—chlorarachniophyceae
Chlorarachniphyceae are naked, uninucleate cells that form a net-like plasmodium via filopodia (Figures
1.1bf, 1.53a, and 1.53b). The basic life cycle of these algae comprises ameboid, coccoid, and flagellate
cell stages. The ovoid zoospores bear a single flagellum that during the swimming wraps around the
cell. Chlorachniophytes are marine. They possess chlorophyll a and b. Each chloroplast has a prominent projecting pyrenoid and is surrounded by four envelope membranes. Thylakoids are grouped in
stacks of 1–3. A nucleomorph is present between the second and third membranes of the chloroplast
envelope. The origin of this organelle is different from the origin of the cryptophyte nucleomorph, since
the chlorachniophytes came from a green algal endosymbiont. Paramylon (β-1,3-glucan) is the storage
carbohydrate. They can phototrophic and phagotrophic, engulfing bacteria, flagellates, and eukaryotic
algae. Asexual reproduction is carried out by either normal mitotic cell division or zoospore formation.
Sexual reproduction characterized by heterogamy has been reported for only two species.
myzozoa—dinophyceae
Dinophyceae are typical unicellular flagellates, but can be also nonflagellate, ameboid, coccoid,
palmelloid, or filamentous (Figures 1.1bg, 1.1bh, 1.54, and 1.55). Dinoflagellates have two flagella
with independent beating pattern, one training, one girdling that confer characteristic rotatory
swimming whirling motion. Flagella can be apically inserted (desmokont-type) or emerging from
a region close to the midpoint of the ventral side of the cell (dinokont-type). Most dinoflagellates
are characterized by cell-covering components that lie beneath the cell membrane. Around the cell,
there is a superficial layer of flat, polygonal vesicles, which can be empty or filled with cellulose
plates. In dinokont-type dinoflagellates, these thecal plates generally form a bipartite armor, consisting of an upper, anterior half and a lower, posterior half, separated by a groove known as cingulum,
where the transversal flagellum is located (Figure 1.55). A smaller groove, the sulcus, extends posteriorly from the cingulum and hosts the longitudinal flagellum. The two flagella emerge from a pore
located at the intersection of the two grooves. Very often dinoflagellates are important components
of the microplankton of freshwater and marine habitats. Though most are too large (2–2000 μm) to
be consumed by filter feeders, they are readily eaten by larger protozoa, rotifer, and planktivorous