Volvox sp. Linnaeus, 1758
Volvox is a colonial organism with up to 50,000 Chlamydomonas-like cells arranged at the periphery of a hollow spherical matrix made up of gelatinous polysaccharide. The cells have their flagells projecting outside the surface of the matrix and the colony swims in a well coordinated fashion. The cells towards the anterior pole have more developed eyespots than those towards the posterior, thus enabling the colony to swim towards the light. In some species the individual cells are connected by thin cytoplasmic strands.
This is a freshwater colonial alga that can be found in ditches, ponds and shallow puddles.
Certain cells of the colony have the ability to divide asexually to form daughter colonies. Initially these daughter colonies remain within the coenobium, with the flagella of the cells directed inwards. The daughter colonies are only released when the mother colony disintegrates. Following release, the daughter colonies invert such that the flagella of the cells point outwards. In sexual reproduction, special cells either develop into numerous sperms or single eggs or both, depending on the species. The male reproductive cells are released into the water but the female cells are retained within the colony. The sperms seek out the eggs and fertilise the eggs inside the colony Once the zygotes develop, the colony eventually disintegrates and the zygotes drift away to form individual colonies.
Bold, H. C., C. J. Alexopoulos & T. Delevoryas, 1987. Morphology of plants and fungi. Harper & Row, New York. (5th ed.). 912pp.