Pandorina is a genus of green algae in the family Volvocaceae. It is a common freshwater genus, and has a cosmopolitan distribution.[ Along with other algae such as Volvox, Eudorina and Chlamydomonas, it is a model organism for studying the origins and evolution of multicellularity.]
Description
Pandorina is composed of 8, 16, or sometimes 32 cells, held together at their bases to form a globular or ellipsoidal colony surrounded by mucilage. The cells are ovoid or slightly narrowed at one end to appear keystone- or pear-shaped. Each cell has two flagella with two contractile at its base, an eyespot, and a large cup-shaped chloroplast with at least one pyrenoid.[ The colonies co-ordinate their flagellar movement to create a rolling, swimming motion. Pandorina shows the beginnings of the colony polarity and differentiation seen in Volvox, with anterior cells having larger eyespots.
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Asexual reproduction is by simultaneous division of all cells of the colony to form autocolonies that are liberated by a gelatinization of the colonial envelope. Sexual reproduction occurs by division of each cell of the colony into 16-32 .[Smith, GM. Phytoplankton of Inland Lakes of Wisconsin, Part I, Wisconsin Geological and Natural History Survey, Madison, WI. (1920).] Sexual reproduction is isogamous.[
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Taxonomy
The taxonomy of Pandorina and Eudorina have been confused because the original description was insufficient to distinguish the two genera.[ In addition, some species appear to be intermediate in morphology between the two, and have at times been considered part of either genus, such as Pandorina/Eudorina charkowiensis. Currently, these intermediate taxa are placed in two genera, Colemanosphaera and Yamagishiella. Therefore, the genera are separated as follows:]
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Pandorina: two contractile vacuoles at the base of the flagella; one or multiple pyrenoids; sexual reproduction isogamous;
[ no cellular envelope around each individual cell.][
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Colemanosphaera: two or three contractile vacuoles at the base of the flagella; multiple pyrenoids in a mature cell; sexual reproduction anisogamous, with fertilization happening outside of the female spheroid; cellular envelope around each individual cell.
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Yamagishiella: two contractile vacuoles at the base of the flagella; single basal pyrenoid; sexual reproduction isogamous; cellular envelope around each individual cell.
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Eudorina: two apical contractile vacuoles and multiple contractile vacuoles scattered throughout cell; one basal or multiple pyrenoids;
[ cellular envelope around each individual cell.][
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Molecular sequencing has shown that Pandorina is paraphyletic with respect to Volvulina.
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