Range of Thallus Structure
in Algae
Range of Structure in Algae
There is a great diversity in the
thallus structure in algae. They vary
from tiny single-celled species one
micrometer in diameter to giant
seaweeds over 50 meters long e.g.
Macrocystis. Broadly, all algae may
be divided into two types regarding
their structure.
There are two types of
algae regarding their
structure.
(1) Unicellular Algae
(2) Multicellular Algae
1) Unicellular Algae: These are of
following two types:
(a) Non-motile: Non-motile unicells
(without flagella — organ for
locomotion). Many unicellular algae do
not possess any outgrowth for
locomotion. Example – Chlorella.
Chlorella
b) Motile: These algae are single cells. All
the vital function of life are performed by
the single cell The unicellular algae are all
sizes and shapes. They range from small
spherical cells to large irregular shaped cells.
The unicellular forms may be spherical,
oblong, pear-shaped or sometimes
elongated bearing flagella
eg. Chlamydomonas, Euglena, Carteria.
Chlamydomonas
Euglena
Carteria
A Unicellular
alga with 4
flagella
(2) Multicellular Algae:
These are of following kinds:
(a) Non-motile Colony:
Number of cells in these
colonies is indefinite and they
are non motile e.g.
Hydrodictyon, Pediastrum.
Hydrodictyon
Pediastrum
(b) Motile Colony:
In these algae, definite
number of cells are found
and these are motile, e.g.
Scenedesmus, Gonium
(small colony), Volvox (big
colony).
Scenedesmus
Only 4-celled colony
Gonium
A 16 celled colony
Volvox
(c) Amorphous Colony:
They are also called as
Palmelloid forms: Algae cells
in these are surrounded by a
viscous mucilalginous
substance e.g. Microcystis,
Tetraspora.
Microcystis
Colony
Individual cells
Tetraspora
(d) Dendroid colony:
Cells of these forms produce
mucilaginous substance and
are folded in such a manner
that they look like branches
of a plant, e.g. Dinobryon.
Dinobryon
(e) Filamentous:
Filamentous algae (floating or attached. The
simplest filamentous algae consist of a
thallus (body) of a single chain of cells. This
is the result of cell division in one plane only.
The filaments may be Unbrached
filamentous forms :-Such type of thalli are
found in many algae and consist of a straight
row of cells. As a free living e.g. Spirogyra
or attached e.g. Ulothrix and Oedogonium.
Ulothrix
An Attached
alga
Holdfast Cell
Substratum
Oedogonium
An Attached alga
These are of following types:
(i) Simple Unbranched
filaments, e.g. Ulothrix
(ii) Simple branched filaments,
e.g. Cladophora
(iii) Psudobranched filaments,
e.g.
Scytonema
Ulothrix
Unbranched
filamentous
alga with
clear girdle
shape
chloroplast
and nucleus
Cladophora
Scytonema
Showing
Psuedobranching
(Not truly branched)
(iv) Heterotrichous forms
(heteros =different): Some cells in
the filaments divide several times
in different planes resulting in two
parts. Thallus consists of two parts,
i.e. horizontally running main
shoot/trichome and a vertical erect
trichome/shoot e.g.
Draparnaldiopsis, Chara
Draparnaldiopsis
Chara
(f) Siphonous or Siphonaceous:
The thallus undergoes repeated
nuclear division without the
accompanying formation of cell
walls. As a result tubular structure
with the multinuclear cytoplasm
lining is formed known as
coenocytic as in siphonales e.g.
Vaucheria, Caulerpa.
Vaucheria
Caulerpa
Valonia
(g) Parenchymatous:
Seaweeds made up of "boxy" cells like
those of higher plants are termed
parenchymatous. They may be
membranous like Ulva, the sea lettuce.
In these algae, cell division takes place
on different sides with the result that
they become parenchymatous, e.g. Ulva,
Macrocystis.
Ulva
Macrocystis
(g) Psuedoparenchymatous:
Psuedoparenchymatous algae
have thalli that superficially
resemble parenchyma, but which
are actually composed of
appressed filaments or
amorphous cell aggregates. e.g.
Monostroma
Monostroma