36
Algae
short smooth one that points backwards along the cell. These algae are mostly marine, but they can
also be found in freshwater and terrestrial habitats. They show a preponderance of carotenoids over
chlorophylls that result in all groups having golden rather than grass green hue typical of other major
algal division. The members of this division possess chlorophylls a, c 1 , c 2 , and c 3 with the exception of the Eustigmatophyceae, Aurearenophyceae, and Ochromonas (Chrysophyceae) that have only
chlorophyll a. The principal accessory pigments are β-carotene, fucoxantin, and vaucheriaxanthin.
The chloroplast is surrounded by four membranes: the normal plastidial double-membrane envelope,
surrounded by a periplastidial membrane and by rough ER, which may be continuous with the outer
membrane of the nuclear envelope. The periplastidial membrane is considered to be the remnants of
the eukaryotic endosymbiont’s (a red alga) plasmalemma. The chloroplast interior is occupied by thylakoids, which are grouped into stacks of three, called lamellae. One lamella usually runs along the
whole periphery of the chloroplast, and is termed girdle lamella, absent only in the Eustigmatophyceae.
The chloroplastic DNA is usually arranged in a ring-shaped nucleoid. Dictyochophyceae species possess several nucleoids scattered inside the chloroplast. The main reserve polysaccharide is chrysolaminarin, a β-1,3-glucan, located inside the cytoplasm in special vacuoles. The eyespot consists of a
layer of globules, enclosed within the chloroplast, and together with the photoreceptor, located in the
smooth flagellum, forms the photoreceptive apparatus. The member of this phylum can grow photoautrophycally, but can also combine different nutritional strategy such as heterotrophy (phagotrophy).
The Ochrophyta species that reproduce sexually have a haplontic (e.g., Chrysophyceae), diplontic
(e.g., Bacillariophyceae), or diplohaplontic (e.g., Phaeophyceae) life cycles. Chrysophyceae are predominantly single-celled flagellate individuals, but also coccoid, filamentous, and parenchymatous
(Figures 1.1ai and 1.3). Most of these algae lack cell walls and have flagella inserted apically or slightly
subapically. Cell coverings, when present, include organic scales, organic lorica, and cellulose cell
wall. Xanthophyceae can be unicellular coccoids or flagellate, ameboid, or filamentous, but the most
distinctive species are siphonous (Figures 1.1al and 1.18). Most Xanthophyceae are freshwater or soil
algae, but a few are marine. All known species of Eustigmatophyceae are green coccoid unicells
either single, in pairs or in colonies, which exhibit little morphological diversity (Figures 1.1am and
1.2). They are found in fresh, brackish, and seawater, as well as soil environments. Bacillariophyceae
or diatoms are a group of unicellular brown pigmented cells that are encased by a unique type of
silica wall, composed of two overlapping frustules that fit together like a box and lid (Figures 1.1an,
1.48, and 1.49). They are both marine and freshwater. Raphidopyceae are all unicellular autotrophic
cells (Figures 1.1ao and 1.50), relatively big in size (30–80 μm), and globoid to ovoidal elongated
shaped. Sometimes, they show a more sharpened point with a curved dorsal side and a flat ventral
FIGURE 1.48 Marine diatom. Scale bar: 10 μm.
Algae
short smooth one that points backwards along the cell. These algae are mostly marine, but they can
also be found in freshwater and terrestrial habitats. They show a preponderance of carotenoids over
chlorophylls that result in all groups having golden rather than grass green hue typical of other major
algal division. The members of this division possess chlorophylls a, c 1 , c 2 , and c 3 with the exception of the Eustigmatophyceae, Aurearenophyceae, and Ochromonas (Chrysophyceae) that have only
chlorophyll a. The principal accessory pigments are β-carotene, fucoxantin, and vaucheriaxanthin.
The chloroplast is surrounded by four membranes: the normal plastidial double-membrane envelope,
surrounded by a periplastidial membrane and by rough ER, which may be continuous with the outer
membrane of the nuclear envelope. The periplastidial membrane is considered to be the remnants of
the eukaryotic endosymbiont’s (a red alga) plasmalemma. The chloroplast interior is occupied by thylakoids, which are grouped into stacks of three, called lamellae. One lamella usually runs along the
whole periphery of the chloroplast, and is termed girdle lamella, absent only in the Eustigmatophyceae.
The chloroplastic DNA is usually arranged in a ring-shaped nucleoid. Dictyochophyceae species possess several nucleoids scattered inside the chloroplast. The main reserve polysaccharide is chrysolaminarin, a β-1,3-glucan, located inside the cytoplasm in special vacuoles. The eyespot consists of a
layer of globules, enclosed within the chloroplast, and together with the photoreceptor, located in the
smooth flagellum, forms the photoreceptive apparatus. The member of this phylum can grow photoautrophycally, but can also combine different nutritional strategy such as heterotrophy (phagotrophy).
The Ochrophyta species that reproduce sexually have a haplontic (e.g., Chrysophyceae), diplontic
(e.g., Bacillariophyceae), or diplohaplontic (e.g., Phaeophyceae) life cycles. Chrysophyceae are predominantly single-celled flagellate individuals, but also coccoid, filamentous, and parenchymatous
(Figures 1.1ai and 1.3). Most of these algae lack cell walls and have flagella inserted apically or slightly
subapically. Cell coverings, when present, include organic scales, organic lorica, and cellulose cell
wall. Xanthophyceae can be unicellular coccoids or flagellate, ameboid, or filamentous, but the most
distinctive species are siphonous (Figures 1.1al and 1.18). Most Xanthophyceae are freshwater or soil
algae, but a few are marine. All known species of Eustigmatophyceae are green coccoid unicells
either single, in pairs or in colonies, which exhibit little morphological diversity (Figures 1.1am and
1.2). They are found in fresh, brackish, and seawater, as well as soil environments. Bacillariophyceae
or diatoms are a group of unicellular brown pigmented cells that are encased by a unique type of
silica wall, composed of two overlapping frustules that fit together like a box and lid (Figures 1.1an,
1.48, and 1.49). They are both marine and freshwater. Raphidopyceae are all unicellular autotrophic
cells (Figures 1.1ao and 1.50), relatively big in size (30–80 μm), and globoid to ovoidal elongated
shaped. Sometimes, they show a more sharpened point with a curved dorsal side and a flat ventral
FIGURE 1.48 Marine diatom. Scale bar: 10 μm.