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Flagellated colonies in the 'volvocine line' are considered to have arisen from the unicell predecessor Chlamydomonas and ending with Volvox spp. with its communication network of plasmodesmata interconnecting all cells. The proportion of reproductive cells decreases along the way, with Volvox having the fewest ‘gonidia’ out of >1,000 (up to 50,000) somatic flagellated cells. Most colonies are hollow spheres with a single layer of flagellated cells on the periphery. Exceptions are Platydorina and Gonium with flattened 2D colonies one cell thick, and Pyrobotrys and Spondylomorum with a 3D cluster of cells lacking a hollow center of the colony. Movement of the spherical flagellated colonies is always clockwise as the colonies move forward in a right-handed helical pattern resulting from the right-hand orientation of all flagella. Phototaxis is achieved by changing the rate of beat of the flagella, not by a change in their spatial orientation (Gerisch 1959).
REFERENCES
Gerisch, G. 1959. Die Zelldifferenzierung bei Pleodorina californica Shaw and die Organisation der Phytomonadinenkolonien. Archiv fur Protistenkunde 104:292-358. online
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