35
General Overview
swelling is present. The most important storage product is the polysaccharide chrysolaminarine.
The cell surface is typically covered with tiny cellulosic scales or calcified scales bearing spoke-like
fibrils radially arranged. Most haptophytes are photosynthetic, but heterotrophic nutrition is also
possible. Phagothropy is present in the forms that lack a cell covering. A heteromorphic diplohaplontic life cycle has been reported, in which a diploid planktonic flagellate stage alternates with a
haploid benthic filamentous stage.
crypTophyTa
The unicellular flagellate belonging to the division Cryptophyta are asymmetric cells dorsiventrally
constructed (Figure 1.47). They are mostly biflagellated, with two unequal, hairy flagella, subapically inserted, emerging from above a deep gullet located on the ventral side of the cell. The wall
of this gullet is lined by numerous ejectosomes similar to trichocysts. Cryptophytes are typically
free-swimming in freshwater and marine habitats; palmelloid phases can also be formed, and some
members are known to be zooxanthellae in host invertebrates or within certain marine ciliate.
These algae possess only chlorophyll a and c 2 . Phycobilins are present in the thylakoid lumen
rather than in phycobilisomes. The chloroplasts, one or two per cell, are bounded by four membranes. The outermost membrane is continuous with the nuclear envelope and its surface is studded
with ribosomes. Between the inner and outer membrane pairs is the periplastidial compartment,
which contains the nucleomorph, the relict nucleus of the eukaryotic endosymbiont. Thylakoids
are arranged in pairs, with no girdle lamellae. The pyrenoid projects out from the inner side of the
chloroplast. The chloroplast DNA is condensed in small nucleoids scattered inside the chloroplast.
The reserve polysaccharide accumulates in the periplastidial space as starch granules. Sometimes
an eyespot formed by spherical globules is present inside the plastid, but it is not associated with
the flagella. The cell is enclosed in a stiff, proteinaceous periplast, made by polygonal plates. Most
forms are photosynthetic, but there are some colorless, heterotrophic. The primary method of reproduction is simply by longitudinal cell division, but sexual reproduction has also been documented.
ochrophyTa
One of the defining features of the members of this division is that when two flagella are present,
they are different. Flagellate stages, when present, are therefore termed heterokont, that is, they
possess a long mastigonemate flagellum, which is directed forward during the swimming, and a
FIGURE 1.47 Unicell of Cryptomonas sp. Scale bar: 6 μm.
General Overview
swelling is present. The most important storage product is the polysaccharide chrysolaminarine.
The cell surface is typically covered with tiny cellulosic scales or calcified scales bearing spoke-like
fibrils radially arranged. Most haptophytes are photosynthetic, but heterotrophic nutrition is also
possible. Phagothropy is present in the forms that lack a cell covering. A heteromorphic diplohaplontic life cycle has been reported, in which a diploid planktonic flagellate stage alternates with a
haploid benthic filamentous stage.
crypTophyTa
The unicellular flagellate belonging to the division Cryptophyta are asymmetric cells dorsiventrally
constructed (Figure 1.47). They are mostly biflagellated, with two unequal, hairy flagella, subapically inserted, emerging from above a deep gullet located on the ventral side of the cell. The wall
of this gullet is lined by numerous ejectosomes similar to trichocysts. Cryptophytes are typically
free-swimming in freshwater and marine habitats; palmelloid phases can also be formed, and some
members are known to be zooxanthellae in host invertebrates or within certain marine ciliate.
These algae possess only chlorophyll a and c 2 . Phycobilins are present in the thylakoid lumen
rather than in phycobilisomes. The chloroplasts, one or two per cell, are bounded by four membranes. The outermost membrane is continuous with the nuclear envelope and its surface is studded
with ribosomes. Between the inner and outer membrane pairs is the periplastidial compartment,
which contains the nucleomorph, the relict nucleus of the eukaryotic endosymbiont. Thylakoids
are arranged in pairs, with no girdle lamellae. The pyrenoid projects out from the inner side of the
chloroplast. The chloroplast DNA is condensed in small nucleoids scattered inside the chloroplast.
The reserve polysaccharide accumulates in the periplastidial space as starch granules. Sometimes
an eyespot formed by spherical globules is present inside the plastid, but it is not associated with
the flagella. The cell is enclosed in a stiff, proteinaceous periplast, made by polygonal plates. Most
forms are photosynthetic, but there are some colorless, heterotrophic. The primary method of reproduction is simply by longitudinal cell division, but sexual reproduction has also been documented.
ochrophyTa
One of the defining features of the members of this division is that when two flagella are present,
they are different. Flagellate stages, when present, are therefore termed heterokont, that is, they
possess a long mastigonemate flagellum, which is directed forward during the swimming, and a
FIGURE 1.47 Unicell of Cryptomonas sp. Scale bar: 6 μm.