Capsid
Capsids are broadly classified according to their structure. Some viruses, such as bacteriophages, have developed more complicated structures.  The icosahedral shape, which has 20 equilateral triangular faces, approximates a sphere, while the helical shape is cylindrical.  The capsid faces may consist of one or more proteins. For example, the foot-and-mouth disease virus capsid has faces consisting of three proteins called VP1–3.