Final answer:
The 20-sided figure with 12 evenly spaced corners is known as an icosahedral capsid, which is efficient for virus structure and genome compactness.
Step-by-step explanation:
One of the principal capsid shapes, a symmetrical solid shape with 20 faces and 12 evenly spaced corners, is referred to as a icosahedral capsid. This structure is composed of equilateral triangular faces that meet at the corners, resembling a soccer ball. The icosahedral shape is notably efficient for creating a structurally robust form using multiple copies of a single protein, which is fundamental for the assembly of viral capsids. This design is advantageous because it saves space in the viral genome, allowing for the construction of the capsid from a repeated basic unit protein.