A small crustacean very much resembling the lobster, but less indigestible.
In this small fish I take it that human wisdom is admirably
figured and symbolized; for whereas the crayfish doth move only
backward, and can have only retrospection, seeing naught but the
perils already passed, so the wisdom of man doth not enable him to
avoid the follies that beset his course, but only to apprehend
their nature afterward.
Sir James Merivale
—Ambrose Bierce, The Devil's Dictionary