The outliers discussed in the text (Rotavirus VP4/VP7 and Astrovirus VP27) are non-enveloped but were "misclassified" as Enveloped. Picornaviridae (which make up the bulk of the non-enveloped set) have rigid "canyon" capsids. Rotavirus and Astrovirus (the "misclassified" non-enveloped viruses) have protruding spikes, structurally similar to enveloped glycoproteins. This suggests a highly plausible biological explanation: the clustering is not driven by the presence of a lipid "Envelope," but rather by "Structural Protrusion / Spike Architecture."
We don't disagree. Clarify this explanation in the Discussion section.
We don't disagree. Clarify this explanation in the Discussion section.