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Euglenophyta
The members of Euglenophyta
are known as:
Euglenoids
Euglenids
Euglenophytes
Euglenoid flagellates
Only about one third of the
known genera possess
green-pigmented
chloroplasts. Of the rest,
many contain colorless
plastids, and others lack
plastids altogether.
Euglenoid cell contains
eukaryotic mitochondria,
cytoskeletal systems,
9+2 flagella, and
endomembrane systems,
including Golgi bodies.
The 9+2 arrangement of microtubules in a flagellum
Euglenophyta are various types of
the distinctive, primarily unicellular
algae and are found in any wetland
area, including marshes, swamps
(area of soft wet land), fens (area of
low marshy land), and bogs or
mires(wet spongy ground formed of
decaying vegetation).
Indeed, euglenoids are
generally found in
environments where
there is an abundance
of decaying organic
matter.
Because of their association with
increased levels of dissolved organics,
euglenoids have been used as
environmental indicators of such
conditions. Environments high in
decaying organic materials suit the
needs of euglenoids because they all
require vitamins B1 and B12, which are
released by the activity of associated
microbial floras.
A number of euglenoid genera are
phagotrophic (i.e., they feed upon
organic particles) and consequently
possess cellular organelles that are
specialized for capture and
ingestion of prey, including bacteria
and small algal cells.
Cell Structure
Euglena move by a flagellum which is
a long whip-like structure that acts like
a little motor. The flagellum is located
on the anterior (front) end, and twirls
in such a way as to pull the cell
through the water. It is attached at an
inward pocket called the reservoir.
The Euglena is unique in that it is
both heterotrophic (must
consume food) and autotrophic
(can make its own food).
Chloroplasts within the euglena
trap sunlight that is used for
photosynthesis, and can be seen
as several rod like structures
throughout the cell.
Euglena also have an eyespot at
the anterior end that detects light,
it can be seen near the reservoir.
This helps the euglena find bright
areas to gather sunlight to make
their food. Color the eyespot red.
Euglena can also gain nutrients
by absorbing them across their
cell membrane, hence they
become heterotrophic when
light is not available, and they
cannot photosynthesize.
The euglena has a stiff pellicle
outside the cell membrane that
helps it keep its shape, though the
pellicle is somewhat flexible and
some euglena can be observed
scrunching up and moving in an
inchworm type fashion. Color the
pellicle blue.
In the center of the cell is the
nucleus, which contains the
cell's DNA and controls the
cell's activities. The nucleolus
can be seen within the
nucleus.
Some Members of Euglenophyta
Euglena gracilis
Petalomonas
Entosiphon
With 2 flagella
Astasia
Like Euglena but lacks plastids and light-sensing
system
Trachelomonas
Green
pigmented
cells are
encased
within a rigid,
mineralized
ornamented
‘lorica’
Phacus
= Lentil; single flagellum, many chloroplasts
Reproduction
in Euglena
Sexual reproduction does not
occur in euglenoids with
regularity, if at all. Asexual
reproduction is by longitudinal
division, proceeding from apex
to base, such that euglenoids in
the process of cytokinesis
appear to be "two-headed".
Chromosomes of euglenoids are
unusual in that they are
permanently condensed, i.e., they
do not undergo cell-cycle changes
in DNA coiling as do those of most
eukaryotes.
Prior to mitosis, the nucleus
migrates to the region just
below the cell pocket
(reservoir); the nuclear
envelope does not break down
during mitosis, as it does in
some other protists, animals,
and land plants.
Often, a pair of basal bodies (that
have replicated prior to nuclear
division) forms each of the spindle
poles. The spindle develops within
the confines of the nuclear envelope,
lying at right angles to the long axis
of the cell. Following chromosomal
separation, daughter nuclei form by
central constriction of the parental
nucleus.
(a, b) Two stages of
mitosis in Euglena.
Mitosis is "closed,"
i.e., the nuclear
envelope remains
intact. The spindle
is intranuclear.
The cleavage
furrow shown in (b)
splits the cell
longitudinally
The End