- Living or growing on the external surface of an animal.
- In <em>natural history</em>, living on the surface or in the skin of animals, as lice, ticks, and many other insects, various parasitic fungi, etc. Also <internalXref urlencoded="epizo%C3%B6tic">epizoötic</internalXref>.
- Specifically, of or pertaining to the crustaceous parasites known as <em>Epizoa.</em>
- Also <em>epizoal, epizoan.</em>
- Living upon the exterior of another animal; ectozoic; -- said of external parasites.
- <xref>living</xref> or <xref>growing</xref> on the <xref>external</xref> <xref>surface</xref> of an <xref>animal</xref> (not always as a <xref>parasite</xref>)
- living or growing on the exterior surface of an animal usually as a parasite