This document describes the genus Volvox, which are colonial green algae found in freshwater. Volvox colonies are spherical or elliptical in shape, made up of 500-50,000 cells embedded in mucilage. Each cell performs functions like nutrition, respiration, and excretion. Sexual reproduction is oogamous and heterothallic or homothallic, involving female oogonia and male antheridia that produce sperm. Fertilization results in a zygote that forms a dormant oospore, which can germinate to form a new Volvox colony.

1. Class- Chlorophyceae
Order- Volvocales
Family- Volvocaceae
VOLVOX

2.  Colonial-hollow sphear with mucilage
 Fresh water
 Found in ponds, lakes, tanks,puddles,pools etc.
 Blooms during favourable condition
 Float during day – deep during night
 6/20
 V. africanus, V. prolificus, V. merelli, V.
globator, V rouseletii,
OCCURRENCE

3.  Colonial, spherical or broadly elliptical
 Macroscopic –pin head – 0.5- 1.5 mm
 500 – 50000 chlamydomonas like cells
 Haploid gametophyte
 Arrangement is definite
 Coenobium (specific arrangement and definite number
 Embeded in a mass of mucilage
 Each cell surrounded by mucilage sheath
 Each cell of coenobium performs its own function of nutrition,
respiration & excretion
 Cells are inter connected by plasmodesmata
STRUCTURE

5. Single layer along the periphery
Centre hollow- mucilage/gelatinous (V. aureus) / water (V.globator)
Cells
Chlamydomonas- anterior pointed, posterior rounded
Anterior thick cell wall Papilla , apair of contractile vacuoles
Anterior two flegella = in length - from basal granules
Nucleus at the centre
Cup shaped chloroplast-posterior- anterior eye spot central pyrinoid
Chlo a, b. Carotenes, xanthophylls
Starch

6. During favourable condition
Posterior end of colony
2- 20 cells - gonidia
 Lack eye spot, flegella, more
pyrinoids
 2,4- 8- curved plate(plakea
stage)/octant stage
 Central hollow and pore anterior
(Phialopore)
 Anterior end towards hollow
space- cruciate plakea stage
ASEXUAL GONIDIA
REPRODUCTION

7.  Sphere cell turn completely
inside out through phialopore
 Develop eye spot and flegella
 Duaghter colony inside the
gonidial wall
 Release through repture
INVAGINATION/INVERSION

8. Oogamous
End of the season
Homothallic (V. globator)
Heterothallic (V. aureus)
Monoecious – protandrous
V. aureus- Protogynous
Male- antheredium
Female – oogonium
Haploid gametophyte
SEXUAL
REPRODUCTION

9. Posterior part of the colony
From vegetative cell
Loss flegella – antheridial cell
Protoplast divides Mitotically
16 - 128 /512
Secrete cell wall, flegella – sperms
Curved plate
Liberate clusters
Yellow in colour
ANTHERIDIUM/ ANDROGONIDIA

10. Posterior
Develops to oogonial cell
Loses flegella, eye spot
Protoplast gets rounded- egg /
ovum
Haploid
Peripheral chloroplast
Yellow
OOGONIUM / GYNOGONIDIA

12. Chemotactic stimulations
Only one fuse
ZYGOTE
Secrete thick wall- oospore
Haematochrome- red
May go to dormant stage
FERTILIZATION

13. V. minor, V. aureus –new colony as
asexual
V.Rousseletii- 4 haploid- 1 survive –
form zoo spore / meiospore
/swarmer– new coenobium
Paethenogenesis reported from
V.aureus
GERMINATION OF ZYGOT

14. LIFE CYCLE