Assertion: goldfish's ancestor | /r/CapableOf | think to be the protovertebrate
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Source sentences:
text: The ancestors of modern hagfish, thought to be the protovertebrate were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one.