A brief account of the general characters of Bacillariophyceae & Pinnularia.

1. General Characters of Bacillariophyceae
&
Pinnularia
Dr Saji Mariam George
Associate Professor (Retired)
Assumption College Autonomous
Changanacherry

2. CLASS BACILLARIOPHYCEAE
• 200 genera
16,000 sps.
• Popularly
known as
Diatoms – ‘The
Jewels of Plant
Kingdom’ - Cell
wall has silica
deposits and
are beautifully
sculptured. Posted on August 17, 2015 by Katherine Faull
https://www.sciengist.com

3. CLASS BACILLARIOPHYCEAE
DIATOMS
General Characters
i) Habitat
• Aquatic – freshwater, brackish water
(water that has more salt than freshwater ,
but not as much as sea water )and marine.
 Many are planktonic.
 Some are benthic forms - attached to
mud, sand, rocks.

4.  Some are epiphytes attached by the
mucilage covering of the frustule or by a
mucilagenous stalk secreted by the Diatom .
Some are epizoic.
A few are symbionts in marine protozoans.
• Terrestrial – sub aerial – confined to moist
places.

5. ii) Habit / Thallus organization / Range of
Thallus structure :
• Microscopic
• Unicellular, diploid thallus .
• Isolated , pseudofilaments or colonies –
several unicellular thalli may be held
together by mucilage.

6. Variously coloured, diverse forms- like
triangular, circular, semi-circular, disc –like,
boat –like etc.

7. Diploneis
photo by Y. Tsukii
Protist Information Server
http://protist.i.hosei.ac.jp

8. Navicula

9. Cymbella
Saved from protist.i.hosei.ac.jp
https://www.pinterest.com.au

10. Triceratium

11. Cells may be Radially symmetrical - Order
Centrales (Centric diatoms) e.g. Cyclotella
http://elmodernoprometeo.blogspot.com

12. Cells may be bilaterally symmetrical
Order Pennales (Pennate diatoms) –
e.g. Pinnularia
http://elmodernoprometeo.blogspot.com Protist Information Server
http://protist.i.hosei.ac.jp

13. iii) Cell structure : Cell
wall & Protoplast
The Oceans, Their Physics, Chemistry, and General Biology. New York: Prentice-Hall, c1942 1942.
http://ark.cdlib.org/ark:/13030/kt167nb66r/
The gross structure of a simple diatom (Coscinodiscus). a, valvular view; b, girdle-view
section of cell wall.

14. Coscinodiscus sp. , valvular view
Casco Bay off Falmouth, Maine USA 31 Oct 2007
http://cfb.unh.edu

15. Coscinodiscus sp. , Girdle view
Silicaceous spicules radiate outward in six planes.
http://cfb.unh.edu

16. • Cell wall is secreted by the protoplast.
• Inner pectin and outer silicified (made of
Silica – Silicic acid) cell wall called shell or
frustule or testa.
• The deposition of silicious material occurs
in characteristic patterns or markings
called striae .

17. • Stria (Plural – striae). A row of areolae on
the valve. In Centric diatoms, usually
oriented along radii. In Pennate diatoms,
usually oriented more or less perpendicular
to the apical axis.
• Features of the striae are important in
Diatom taxonomy.

18. Striae
Stephanodiscus
© David G. Mann
http://tolweb.org

19. Gomphosinica geitleri
showing the multiseriate striae.
Image Credit: Marina Potapova
https://diatoms.org

20. • Frustule consists of two overlapping halves -
One of these is older than the other – The
older half fits closely over the younger half
like the lid of a box - the upper epitheca
(epivalve ) and the lower hypotheca
(hypovalve) .
• Each half or theca consists of two parts viz.
valve - the main surface corresponding to
the top or bottom and the connecting bands.

21. • The two connecting bands are firmly united
in the overlapping region called girdle.
• The overlapping upper portions of the
connecting band is called epicingulum and
the lower portions of the connecting band is
called hypocingulum.

23. Image : http://wgbis.ces.iisc.ernet.in

24. • The longitudinal
groove along the
central part of the
valve is called Raphe –
interrupted by
thickening called
nodules.

25. Pinnularia
Image :https://biologyboom.com

26. • In some cases, there
may be outgrowths of
the valves , projecting
beyond the margin,
called setae.
Image : http://nordicmicroalgae.org

27. • Diatoms are unique for their beautifully
sculptured and ornamented cell wall -
Hence they are often referred as the Jewels
of the Plant kingdom.

28. Protoplast
• Living part of the thallus – Plasma membrane
and cytoplasm.
• A large central vacuole.
• A single diploid nucleus.
• Cell organelles – Endoplasmic reticulum,
Ribosomes, Mitochondria, Golgibodies etc.

29. • Chromatophores enveloped by two
membranes– number and shape vary with
species.
• The matrix contain the lamellar system
enclosing the pigments - chlorophyll a, c ,
fucoxanthin , diatomin – the principal
colouring matter, diatoxanthin, carotenoids
etc.
• Generally the diatoms are yellow brown,
golden-yellow or olive -green.

30. • The matrix also contain ribosomes, DNA,
RNAs, enzymes etc.
• Pyrenoids devoid of starch sheath may be
present .
• Reserve Food - Oil, leucosin or
chrysolaminarin , volutin .

31. iv) Movement (Locomotion) :
• Centric diatoms are non motile.
• Pennate forms show gliding movements
produced by cytoplasmic streaming through
the grooves (Raphe) on the surface of the
cell wall – direction of locomotion is
opposite to the direction of cytoplasmic
streaming.

32. v) Reproduction
• Vegetative - Cell division .
• Sexual - Isogamy in Pennales ;Oogamy
in Centrales.

33. i)Vegetative Reproduction or Cell division
• By Fission
• Plane of division is at right angles to the main
axis of the cell.
• Prior to cell division, the cell increases in size
at right angles to the girdle.
• Karyokinesis – the nucleus divides mitotically.

34. • The epitheca and hypotheca separate from
each other.
• Cytokinesis along the median longitudinal
axis - One of the resulting protoplast occupy
the epitheca and the other will occupy the
hypotheca – The missing theca will be soon
secreted by each protoplast which becomes
the hypotheca in each cell.

35. • The daughter cell that has received the parent
epitheca will attain almost the same size of the
parent cell where as the daughter cell that has
received the parent hypotheca will be slightly
smaller in size.
• As a result of cell division, one cell maintains
the size of the parent cell while the other cell
becomes slightly smaller and thus during
successive generations, the size of one of the
daughter cells is progressively reduced.

36. ii) Sexual Reproduction
• Isogamous in Pennales and oogamous in
Centrales.
• Influenced by temperature, light, nutrition etc.
• Most species are homothallic or monoecious.

37. • In both Pennales and Centrales, the zygote
formed by sexual reproduction transforms
to a specialized spore called Auxospore
(Growth spore).
• Auxospore formation is a ‘restorative
process’ for restoring cell size, vitality and
survival ability.

38. • Auxospore formation is associated both with
sexual reproduction and parthenogenesis.
• That is, auxospore is either a modified
zygote or a modified parthenogenetic female
gamete.
Auxospore formation in Pennales

39. 1. Auxospore formation by Syngamy
Types :
i ) Development of a single Auxospore by two
conjugating cells.
• Two conjugating cells come in pair , get
surrounded by a common mucilagenous
sheath and undergo meiotic nuclear
division.
• Of the four haploid nuclei formed in each
cell, three degenerate and the remaining
one transforms to a gamete.

40. • The gametes are liberated – The gametes
fuse forming a zygote.
• After some time the zygote elongates in a
plane , parallel to the long axis of the
parent cell and transforms to an
auxospore.
• During this , it gets enclosed by a silicified
pectic membrane called perizonium.

41. Image :http://bioexampreparation.blogspot.com

42. ii ) Development of two Auxospores by two
conjugating cells.
• Common method of auxospore formation
in Pennales.
• Two cells come in pair, get enveloped by a
common mucilagenous sheath.
• Divide meiotically , producing four haploid
nuclei in each cell – Two nuclei of each
conjugant degenerate.

43. • Cleavage of cytoplasm occurs resulting two
uninucleate cells from each conjugant
which transform into gametes.
• Cross fertilization occurs between the
gametes of the two conjugants resulting in
the formation of two zygotes which
elongate and get encased by perizonium
and transform into auxospores.

44. Image :http://bioexampreparation.blogspot.com

45. iii ) Development of Auxospores by
Autogamy
• Less common in Pennales.
• The cell divide meiotically and form four
haploid nuclei – two nuclei degenerate and
the remaining two fuse to form a zygote.
• The zygote elongates and transforms into
an auxospore.

46. Image: http://bioexampreparation.blogspot.com

47. 2. Auxospore formation by Parthenogenesis
( Apogamy)
• The diploid nucleus undergoes one or more
mitotic divisions and forms daughter nuclei.
• Only one nucleus survives, all other nuclei
degenerate.
• The surviving nucleus get surrounded by
cytoplasm and transforms into an auxospore.

48. Image :http://bioexampreparation.blogspot.com

49. Auxospore formation in Centrales
Auxospore formation is associated only with
sexual reproduction - That is, auxospore is a
modified zygote.
1. Development of Auxospores by Autogamy
• Similar to that in Pennales. The cell divide
meiotically and form four haploid nuclei – two
nuclei degenerate and the remaining two fuse
to form a zygote.
• The zygote elongates and transforms into an
auxospore.

50. 2. Development of Auxospores by Oogamy
• Vegetative cells transform into male sex
organ – antheridium (spermagonium) and
female sex organ – oogonium.
• Diploid cell of antheridium divides
meiotically and form four haploid nuclei –
Each one develop into uninucleate and
uniflagellate antherozoid.
( spermatozoid) . On maturity, antherozoids
are liberated.

51. • In the oogonium, diploid cell divides
meiotically and form four haploid nuclei.
• Of these, three degenerate and the
remaining one transforms into an ovum.
• In some species, after the first meiotic
division, one of the two haploid nuclei
degenerates and the other nucleus divides
into two, of which one degenerates and the
other transforms into an ovum.

52. Image :http://bioexampreparation.blogspot.com

53. • The motile antherozoids swim towards the
ovum and one of them fertilizes it and form
the zygote.
• The zygote elongates, secretes perizonium
and transforms into an auxospore.

54. Germination of Auxospore
• Auxospore enlarges in size and restores the
size of the parent cell.
• The diploid nucleus divide mitotically to
form two daughter nuclei, of which one
degenerates and the other develops into a
diatom.

55. PINNULARIA
Systematic Position
Division : Bacillariophyta
Class : Bacillariophyceae
Order : Pennales
Family : Naviculoideae
Genus : Pinnularia

56. • Typical Pennate Diatom.
• Mostly fresh water forms, a few are marine.
• Unicellular – e.g. Pinnularia viridis
• Colonial – e.g. P. socialis

57. Unicellular Pinnularia viridis Colonial P. socialis

58. • Cells are elongate, elliptical with rounded ends.
• The cell wall has an inner pectic layer and an outer
silica layer.
• The silicious cell wall or Frustule is made up of two
halves or valves, one fitting into other like a box.
• The upper older valve is epitheca or epivalve and
the lower, younger valve is hypotheca or hypovalve.

59. • The two valves instead of overlapping each other
directly, are attached to each other by incurved
edges of the valves called girdles or connecting
bands. (Each valve has two parts viz. a flat
surface called valve face and its margin called
mantle or girdle – The girdle of the two valves
overlap to form the girdle band ) .
• The epicingulum or upper girdle is the side
walls of the epitheca. Hypocingulum or lower
girdle is the side walls of the hypotheca.

60. Image :https://istudy.pk

61. The view of the cell from the top is called valve view and the
view from the side is called girdle view.
Pinnularia -Valve view
Pinnularia - Girdle View
(Side View)
© A.J. Silverside

62. • The longitudinal groove along the central
part of the valve is called raphe. Raphe are
associated with gliding movements. Raphae
are interrupted by thickening called
nodules.
• Raphe has wider outer and inner ends and
narrow middle portion.

63. • Raphe has three round wall thickenings –
nodules - The one situated in the centre
called the central nodule and two located
at the two poles called polar nodules .
• Stria (Plural – Striae). A row of areolae
(fine grooves) , or punctae (tiny holes,
singular: puncta) on the valve – appear
like transverse parallel ribs. The areas
between striae are thickened, rib-like, and
termed costae (singular: costa).

64. Enlarged view of the Striae and rib-like Costae

65. • Inside the cell wall is the protoplast .
• Cytoplasm is located in the periphery.
• The single nucleus is suspended in the
center of the vacuole by a cytoplasmic
bridge.
• A large central vacuole.

66. • Two large, elongated, green or brown
coloured chloroplast are parietal in position
and contain chlorophyll a, chlorophyll c,
beta-carotenes and xanthophylls including
the fucoxanthin which impart the
characteristic color to the thallus.
• One or two pyrenoids may be present.
• The chief food reserve is in the form of oil
drops or chrysolaminarin.

67. PINNULARIA - Movement
(Locomotion)
• The Pinnularia exhibit characteristic
gliding movements which are brought about
by circulation of streaming cytoplasm
within the raphe and by the secretion of the
mucilage through the raphe and its
hydration.

68. PINNULARIA - Reproduction
• Reproduces vegetatively by cell division and sexually by the
production of auxospores.
i) Vegetative Reproduction – Cell division
• This is the most common method of reproduction that results in
the formation of two daughter cells of slightly different size.

69. • The first indication of division, is expansion
of the protoplast that causes a slight
separation of overlapping epitheca and
hypotheca.
• This is followed by mitotic division of the
nucleus in a plane perpendicular to the
valves.

70. • The nuclear division is followed by
duplication of cell organelles.
• Later, the protoplast divides in a plane
parallel to the valves.
• One daughter protoplast lies within the
epitheca and the other within the hypotheca.
• Each daughter protoplast secretes a new
half next to its girdle and free face.

71. • At this stage the parent connecting bands
separate and each cell becomes an
independent cell.
• The two frustules of each parent cell act as
epitheca of the two daughter cells.
• Therefore, newly formed half wall is always
hypotheca of daughter frustule.

72. • The utilization of two old half walls as
epithecae for the daughter cells results in one
cell of the same size as the parent cell and the
other being slightly smaller than the original
parent cell.
• This progressive diminution in size result in a
population with smaller cells, however this
reduction in size does not continue indefinitely.
It is checked by formation of auxospores which
give rise to vegetative cells of maximum size
for the species.

73. Pinnularia - Cell Division

74. ii ) Auxospore ( Renewal spores or
Rejuvenescent cells )formation
• Gradual reduction in the size of cells due to
continuous cell division is compensated by
auxospore formation after sometimes and
thus the normal size is restored.
• Auxospores are formed only when the
individual cells are highly reduced in size.
• During auxospore formation, abundant
mucilage is secreted by the cell.
• This results in pushing the valves apart and
liberation of protoplast.

75. • The protoplast grows to the maximum size of
the particular species of Pinnularia.
• It then surrounded by a silicified pectin
membrane called the perizonium.
• There is no nuclear division.
• The protoplast secretes a fresh epitheca and a
hypotheca and thus a large new Pinnularia cell
is formed.

76. Sexual Reproduction by Auxospore formation
• The sexual reproduction is isogamous and is
influenced by various factors like temperature,
light conditions and nutrition.
The Pinnularia species are monoecious.
• In Pinnularia two cells from common parent
or different parents become enveloped in a
common mucilaginous sheath (conjugation).
• The nuclei of both cells divide by meiosis. Out
of the four haploid nuclei, three disintegrate
and the remaining one transforms into a
gamete.

77. • The gametes are liberated from the parent
frustules and fuse to form a zygote which
transforms into an auxospore.
• The auxospore secretes new valves and form
new Pinnularia cell.
• The auxospore expands to restore the
original cell size of the Pinnularia species.

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