A family of green algae in the order Chlorococcales. Colonial algae usually arranged 3 dimensionally in spherical to loosely spherical shapes. Individual cells connected to each other via cell wall extensions. Cells usually in an even number arrangement. Chloroplasts plate-like with 1 pyrenoid. Name derrived from coelom, in reference to the cavity created inside the sphere. Nonmotile.

Species in this family include:

• Coelastrum morus
• Coelastrum sphaericum
• Coelastrum polychordum
• Coelastrum cambricum
• Coelastrum astroideum
• Coelastrum reticulatum
• Coelastrum microporum
• Coelastrum proboscideum