A peplomer is a glycoprotein spike on a viral capsid or viral envelope.[1] These protrusions will only bind to certain receptors on the host cell: they are essential for both host specificity and viral infectivity. The term 'peplomer' is typically used to refer to a grouping of heterologous proteins on the virus surface that function together.
The tail fibers of some bacteriophages, especially the T4-like phages, are modified peplomers.