Plural of ectozoan; multiple external parasites or the scientific group of organisms that are external parasites.
From ectozoan (adjective/noun) with the standard English plural '-s' added; used primarily in scientific texts from the 19th century onward.
Ectozoans were so important to early parasitology that entire scientific papers were written just cataloging which ones lived on which animals—it's like the Pokemon dex, but itchy!
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