adjective. Living or growing on the external surface of an animal.

In natural history, living on the surface or in the skin of animals, as lice, ticks, and many other insects, various parasitic fungi, etc. Also epizoötic.

Specifically, of or pertaining to the crustaceous parasites known as Epizoa.

Also epizoal, epizoan.

adjective. Living upon the exterior of another animal; ectozoic; -- said of external parasites.

adjective. living or growing on the external surface of an animal (not always as a parasite)

adjective. living or growing on the exterior surface of an animal usually as a parasite

"Unionoidae shells provide a suitable substrate for epiphytic and epizoic colonization, and help stabilize fine-grained sediments that other organisms use for habitat."

ectozoic