What's the difference between homocercal and protocercal?

Homocercal

Definition:

• (a.) Having the tail nearly or quite symmetrical, the vertebral column terminating near its base; -- opposed to heterocercal.

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Protocercal

Definition:

• (a.) Having a caudal fin extending around the end of the vertebral column, like that which is first formed in the embryo of fishes; diphycercal.

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