Platydorina Kofoid
	From Greek platys, "flat" + [pan]dorina
The green alga Platydorina has flattened, horseshoe-shaped colonies made up of 16 or 32 cells arranged in a single, slightly twisted layer. Each cell is spherical or pear-shaped, and bears two equal flagella with two contractile vacuoles at their base, a stigma, and a large cup-shaped chloroplast with a single pyrenoid. The colony is surrounded by mucilage that forms three to five distinctive lobed projections at the posterior end. Platydorina has been found only in the United States and Mexico.
Each cell in a Platydorina colony is capable of forming autocolonies. The new colonies initially form as spheres that subsequently turn inside out and flatten. Sexual reproduction in Platydorina is dioecious and involves gametes that are very similar to the vegetative cells. Sperm packets form walled hypnozygotes, which then germinate and develop via meiosis.