Bacillariophyta PPT BY Dr.Pinky Diwedi

1. Bacillariophyta
M.Sc I sem.unit-II
Dr.Pinky Dwivedi
Botany Department

2. Popularly- diatoms. Aquatic (freshwater or marine)or
terrestrial
Mostly single celled,some filamentous,colonial.
Planktonic or benthic. Some-epiphytic, few epizoic.
Microscopic, variously coloured, diverse in form.
Melosira- half moon shaped;
Triceratium- triangular
Hylodiscus,Cyclotella- circular
Thallus is diploid.
Cell wall is silicified, 2 overlapping halves,
Stored food –oil and chrysolaminarin or volutin (protein like
material).
pigments- chl.a, chl.c, fucoxanthin, carotenoid.yellow-
browm, golden yellow, olive green. accessory brown
pigment diatomin.

3. Motile-single pantonematic flagella
Unique spores- auxospores ,growth spores, zygotic,renewal
spores.
Divided-2 taxonomic groups-centrales
pinnales
Cell- 2 parts- cell wall
protoplast
Cell wall- 2 layers outer ,inner
inner- continous, thin encloses protoplast
outer- 2 overlapping halves, outer half-epitheca
inner half-hypotheca
Protoplast- plasma membrane, cytoplasm, nucleus.
single large nucleus .number and shape of the
chromatophore varies according to the species.

4. Reproduction:
Main mode-asexual-cell division or fission
Asexual spores are not formed.
Cell division- occurs at night, protoplast
increases in size, at the girdle theca slightly
separates, nucleus divides followed by
longitudinal division of the cytoplasm,each
daughter protoplast covers its naked part by
secreting a new theca fitting inside the old
one.New theca is always-hypotheca,
daughter cells now separate.

5. Sexual reproduction: in cell division one of the cells is
smaller in size. Sexual reproduction is the process in
which cell size is restored.It takes place with
formation of auxospores.
it is growth spore.
Pinnales: by gametic union- isogamous, anisogamous
or pedogamous.most spp.-monoecious.fusing
gametes are non-flagellated.
By fussion of iso or anisogametes: 2 or one auxospore
is formed from 2 conjugating indivisuals.
Formation of two auxospores by conjugating
indivisuals- Gomphonema, Cymbella

6. zygote escapes from the enclosing
frustules.then it elongates and functions as an
auxospore.it is enclosed in slightly silicified
pectic membrane- perizonium.
In some spp. Both gametes are amoeboid and
active.These isogametes come out through the
open valves and conjugate,two zygotes are
formed outside the parent frustule.
Formation of a single auxospore by two
conjugating indivisuals.
Formation of a single auxospore from a single
indivisual.

7. Auxospore formation by oogamy.
Rhabdonema adriaticum- dioecious.

8. Auxospore formation by autogamy.
Amphoranormani- cell envelops in
mucilage.diploid nucleus undergoes 1 meiotic
division.two haploid daughter nuclei
fuse(autogamous pairing).this functions as
auxospore which enlrges in size and secretes
afresh frustule within the perizonium.
By parthenogenesis:

9. Auxospore formation in Centrales:
Single auxospore in a single indivisual.By
autogamy or oogamy.
Autogamy- Cyclotella & Melosira
Oogamy- M. varians