Translation of "ápice" in English

Eles são surpreendentemente ágeis, conseguem virar-se num ápice.

They’re actually surprisingly agile, they can spin around pretty much on a 20 cent piece.

Mas alguns destes moluscos só relaxam se a perfuração for mesmo no ápice da concha, no músculo adutor.

But some of these mollusks will only relax if that drill is precisely in the apex of the shell, on the abductor muscle.