Volvox photo by Jack Challoner
Wired has a short blurb featuring some photos from Jack Challoner’s new book The Cell: A Visual Tour of the Building Block of Life, including the above Volvox picture. The caption is
Algae Colonies
Each green sphere is a colony of Volvox algae with more than 50,000 cells. Scientists study these glowing, freshwater organisms as models for how living creatures develop specialized cells and tissue. Strands of cytoplasm connect neighboring cells, allowing them to communicate, and slender flagella propel the colony through the water.
Well, probably not 50,000 in this species, but yes, some Euvolvox (or Section Volvox, as Dr. Nozaki prefers) have that many cells. Models for cellular differentiation, cool (but glowing?). I don’t know of any evidence that cytoplasmic bridges function in cell-cell communication, and it doesn’t look like this species has them in the adults. Cool picture, though!
Let me give a description of Jack Challoner’s Volvox.
Cell number in a great circle is scarcely more than 100. So there seems to be no more than 3700 somatic cells in each colony.
Certainly, there are no thick bridges (typical in the case of the Euvolvox section), but the occurrence of very delicate intercellular bridges (a trait of V. aureus or V. dissipatrix) cannot be completely excluded, though they are invisible in this case.
It is clear that there are no asymmetric divisions in this material. So this is not V. carteri, this is not V. obversus, this is not V. africanus (or V. reticuliferus).
Somatic cell numbers in V. tertius, V. spermatosphaera or V. ovalis would be not as big as in these three colonies. On the other hand, V. dissipatrix would have more cells.
In concluding (and despite the fact that the bridges are invisible), I would say that “Jack Challoner’s Volvox” might be Volvox aureus. Note that this species may have up to approximately 3900 cells in a colony. The golden color of the colonies also supports this idea.
Let me give a description of Jack Challoner’s Volvox.
Cell number in a great circle is scarcely more than 100. So there seems to be no more than 3700 somatic cells in each colony.
Certainly, there are no thick bridges (typical in the case of the Euvolvox section), but the occurrence of very delicate intercellular bridges (a trait of V. aureus or V. dissipatrix) cannot be completely excluded, though they are invisible in this case.
It is clear that there are no asymmetric divisions in this material. So this is not V. carteri, this is not V. obversus, this is not V. africanus (or V. reticuliferus).
Somatic cell numbers in V. tertius, V. spermatosphaera or V. ovalis would be not as big as in these three colonies. On the other hand, V. dissipatrix would have more cells.
In concluding (and despite the fact that the bridges are invisible), I would say that “Jack Challoner’s Volvox” might be Volvox aureus. Note that this species may have up to approximately 3900 cells in a colony. The golden color of the colonies also supports this idea.