Page 43 - Algae

26 Algae: Anatomy, Biochemistry, and Biotechnology

EUGLENOPHYTA
Euglenophyta include mostly unicellular flagellates (Figure 1.39) although colonial species are
common. They are widely distributed, occurring in freshwater, brackish and marine waters, most
soils, and mud. They are especially abundant in highly heterotrophic environments. The flagella
arise from the bottom of a cavity called reservoir, located in the anterior end of the cell. Cells
can also ooze their way through mud or sand by a process known as metaboly, a series of
flowing movements made possible by the presence of the pellicle, a proteinaceous wall which
lies inside the cytoplasm. The pellicle can have a spiral construction and can be ornamented.
The members of this division share their pigmentation with prochlorophytes, green algae, and
land plants, because they have chlorophylls a and b, b- and g-carotenes, and xanthins. However,
plastids could be colorless or absent in some species. As in the Dinophyta the chloroplast envelope
consists of three membranes. Within the chloroplasts, the thylakoids are usually in groups of three,
without a girdle lamella and pyrenoids may be present. The chloroplast DNA occurs as a fine skein
of tiny granules. The photoreceptive system consisting of an orange eyespot located free in the
cytoplasm and the true photoreceptor located at the base of the flagellum can be considered
unique among unicellular algae. The reserve polysaccaccharide is paramylon, b-1,3-glucan,
stored in the granules scattered inside the cytoplasm and not in the chloroplasts like the starch of
the Chlorophyta. Though these possess algae chlorophylls, they are not photoautotrophic but
rather obligate mixotrophic, because they require one or more vitamins of the B group. Some color-
less genera are phagotrophic, with specialized cellular organelle for capture and ingestion of prey;
some others are osmotrophic. Some of the pigmented genera are facultatively heterotrophic. Only
asexual reproduction is known in this division. Euglenophyta posses unique cellular and biochemi-
cal features that place these microorganisms closer to trypanosomes than to any other algal group.

CHLORARACHNIOPHYTA
They are naked, uninucleate cells that form a net-like plasmodium via filopodia (Figure 1.40). The
basic life cycle of these algae comprises ameboid, coccoid, and flagellate cell stages. The ovoid

FIGURE 1.39 Unicell of Euglena mutabilis. (Bar: 10 mm.)