Halosphaera viridis Acetabularia acetabulum
Halosphaera viridis is a small, pear-shaped cell with four swimming flagellae at one end. It reproduces by splitting in two, allowing it to reach high concentrations and from time to time some cells become small cysts whose contents divide into small disks. Each disk eventually becomes a flagellated Halosphaera viridis cell that will be released into the sea. There can be hundreds of cysts per square yard in the open ocean, and they are probably a vital food source for larger zooplankton.