Answer:
I'm pretty sure the answer is the fish group called Agnatha, which includes parasitic fish like lamprey and the hagfish.
Step-by-step explanation:
some include nematodes, Platyhelminthes, leeches, parasitic crustaceans such as isopods and copepods, so also various microorganisms such as myxosporidia and microsporidia. (coral reef fish)
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