Virus structure — The nucleocapsid of certain animal viruses is externally covered by a membrane-like layer called the:

Introduction / Context:
Many viruses acquire an outer lipid bilayer during budding through host membranes. This membrane contains viral glycoproteins essential for entry and immune evasion and is termed the viral envelope.

Given Data / Assumptions:

• “Nucleocapsid” = genome + capsid.
• Some viruses are enveloped (lipid bilayer) and some are non-enveloped (naked).
• The question asks for the standard term for the outer membrane-like covering.

Concept / Approach:
The accepted term is “envelope.” The envelope derives from host membranes (plasma membrane, ER, or Golgi) but is studded with viral proteins that determine host range and antigenicity.

Step-by-Step Solution:

Verification / Alternative check:
Influenza, herpesviruses, and coronaviruses are textbook examples of enveloped virions.

Why Other Options Are Wrong:

• “Covering” and “membronocapsid” are not standard terms in virology.
• “All of these” is invalid because only “envelope” is accepted nomenclature.

Common Pitfalls:
Equating envelope presence with fragility in all environments; while many envelopes are detergent-sensitive, stability varies by virus.

Final Answer:
envelope