Volvox

Volvox - structure, Reproduction

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

4. 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

5. 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

6. Sphere cell turn completely inside out through phialopore Develop eye spot and flegella Duaghter colony inside the gonidial wall Release through repture Invagination/inversion

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

8. 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

9. Posterior Develops to oogonial cell Loses flegella , eye spot Protoplast gets rounded- egg / ovum Haploid Peripheral chloroplast Yellow Oogonium / gynogonidia

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

11. 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

12. Life cycle