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Peplomer [Gr. peplos = robe, (woman’s) dress + Gr. meros = part] (also called a spike) is one of the knoblike structures (spikes), generally composed of glycoproteins (spike protein), projecting from the lipid bilayer of the surface envelope of an enveloped virus. Peplomers play important roles in the infection process; they are responsible for the attachment of the virion to receptor sites on the host cell surface, and they bring about the release of the nucleocapsid into the host cell cytoplasm by triggering fusion between the envelope and host membranes. They may have hemagglutinating activity or have enzyme activity such as neuraminidase. They are surface antigens. 
The term peplomer is rarely used today and is no longer used for all outwardly protruding envelope proteins; it is mostly replaced by the less precise expression spikes. However, this suggests a pointed structure, which is not the case with these envelope structures; they are round, flattened or button-shaped on the outside. Both terms, peplomer and spikes, however, only describe a morphologically visible structure and are not identical to the expression membrane protein or coat protein; many other membrane proteins in viruses do not form these prominent structures.
Peplomers can be seen in electron micrographs on the surface of enveloped viruses such as Orthomyxoviruses, Paramyxoviruses, Rhabdoviruses, Filoviruses, Coronaviruses, Bunyaviruses, Arenaviruses, and Retroviruses.
Influenza virus has two kinds of peplomers:
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