Algal Division V: Chrysophyta

Division V: Chrysopyhta

• Characterized by a wide range of differentiation in various basic taxonomic features, leading some authors to treat some of its six classes as separate divisions.

Class I: Chrysophyceae

• Pigment system composed of chlorophyll A and C, and large amounts of carotenoids and xanthophylls, giving a yellow-green appearance.
• Reserve food material is Chrysolaminarine, oil, and fats.
• Cell wall is composed mainly of cellulose, with two overlapping H-shaped parts in many genera.
• Algae can be unicellular, filamentous, or siphonious, with motile forms having two unequal flagella.
• Asexual reproduction occurs through the formation of zoospores (simple or compound), with sexual reproduction being isogamous, anisogamous, or oogamous.

Order: Vaucheriales, Family: Vaucheriaceae, Genus: Vaucheria

• Siphonous branched alga that inhabits freshwater, marine, and soil habitats.
• Coenocytic structure of filaments, with septa absent except those separating reproductive structures from the main filaments.
• Vegetative reproduction occurs through fragmentation, while asexual reproduction occurs through zoospores formed in zoosporangia.
• Sexual reproduction involves the production of antheridia and oogonia, with fertilization of the ovum and subsequent formation of a zygote.

Class II: Bacillariophyceae

• Unicellular or colonial forms, with a pigment system dominated by carotenes and xanthophylls, giving a golden brown color.
• Reserve food material is Chrysolaminarine, oil, and fats.
• Cell wall is chemically composed of silicon, with motile gametes having a single anterior flagellum.
• Diatoms are diploid in their vegetative phase, with meiosis occurring during gamete formation.
• The rigid cell wall, known as frustules, is composed of two overlapping halves (epitheca and hypotheca) with a girdle area.
• Some pennate diatoms have a fissure known as a raphe, which extends from a central nodule to polar nodules.
• Frustules have markings used in taxonomy.

Habit and Occurrence

• Diatoms are abundant in all waters, both fresh and marine, and form an important element of the plankton flora.
• They are also found in damp soil, rocky walls, dry cliffs, and bark of trees, with some species occurring in hot springs and as epiphytes.
• Many diatoms occur as fossils, forming large deposits known as diatomaceous earth.

Reproduction

• Cell division involves an increase in volume of the frustule, followed by nuclear division, protoplast division, and the formation of two new cells with one old and one new half wall.
• Auxospore formation occurs through sexual reproduction, involving the conjugation of two cells, reductional division, and the formation of gametes, which then unite to form a zygote.
• The zygote elongates into an auxospore, which restores the original size of the diatom.

Economic Importance

• As food: Diatoms are abundant in water and form the food chain of aquatic animals.
• As industrial or commercial value: Diatoms are used in filters, metal polishes, dynamite, insulation, glass, porcelain, paints, toothpaste, and face powder.
• In biology: Diatoms are used to test the efficacy of microscopes, and their cell walls are used to examine the liver oil of fish.