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.
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
4.
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
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
