Page 44 - Algae Anatomy, Biochemistry, and Biotechnology

General Overview 27

FIGURE 1.40 Plasmodial reticulum of Chlorarachnion, bright field microscope image (a) and schematic
drawing (b). (Bar: 4 mm.)

zoospores bear a single flagellum that during swimming wraps around the cell. Chlorarachnio-
phytes are marine. They posses chlorophylls a and b. Each chloroplast has a prominent projecting
pyrenoid and is surrounded by four-membrane envelope. Thylakoids are grouped in stacks of one to
three. A nucleomorph is present between the second and third membranes of the chloroplast envel-
ope. The origin of this organelle is different from the origin of the cryptophytes nucleomorph,
because the chlorarachniophytes originated from a green algal endosymbiont. Paramylon (b-1,3-
glucan) is the storage carbohydrate. They are phototrophic and phagotrophic engulfing bacteria, fla-
gellates, and eukaryotic algae. Asexual reproduction is carried out by either normal mitotic cell div-
ision or zoospore formation. Sexual reproduction characterized by heterogamy has been reported
for only two species.

CHLOROPHYTA
A great range of somatic differentiation occurs within the Chlorophyta, ranging from flagellates to
complex multicellular thalli differentiated into macroscopic organs. The different level of thallus
organization (unicellular, colonial, filamentous, siphonous, and parenchimatous) have traditionally
served as the basis of classification of this division. Prasinophyceae are unicellular motile algae
covered on their cell body and flagella by non-mineralized organic scales (Figure 1.41). The
class Chlorophyceae comprises flagellated cells even naked or covered by a cell wall termed
theca (Figure 1.42). All Ulvophyceae known to date are sessile organisms having walled vegetative
cells. Except for a small group of species, the thalli are usually multicellular or coenocytic during at
least some part of the life history. Many species have microscopic, filamentous thalli, but most are
macroscopic seaweeds, capable of considerable morphological differentiation (Figure 1.22). Clado-
phorophyceae take the form of branched or unbranched filaments of multinucleate cells with
periodic cross walls (Figure 1.11). The organization of the thallus in the class of Briopsidophyceae
is always syphonous; syphonous thalli can combine to form fairly complex tissues (Figure 1.43).
The Zygnematophyceae species are either coccoids or filamentous (Figure 1.8). In all the Trente-
pohliophyceae the thalli consist of branched or unbranched filaments with uninucleate cells