Plural of entozoon; parasitic animals that live inside the bodies of other animals.
From Greek 'entos' (inside) and 'zoon' (animal). This scientific term literally means 'inside-animals' and has been used since the 1700s for parasitic worms and similar creatures.
Tapeworms and roundworms are 'entozoa'—they're animals that live their entire lives inside other animals, which is a pretty wild strategy that worked for millions of years.
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