An animal that is not a vertebrate; an invertebrate; or historically, any animal.
From 'ever' (all) plus 'vertebrate,' an older or variant term for invertebrates. This reflects confusion in early biological taxonomy about what the prefix meant.
Before scientists standardized 'invertebrate,' they used confused terms like 'evertebrate'—this word is basically fossilized linguistic confusion, frozen in old textbooks as a reminder that scientific naming isn't always logical from the start.
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