Answer
A spirochete has axial filaments that help them move that are contained within a flexible external sheath.
Work Step by Step
Spirilla and spirochetes are both flexible and helical but what distinguishes a spirochete is that they have axial filaments to help them move that resemble flagella but are contained within a flexible external sheath, whereas spirilla which have propeller-like external appendages called flagella that help them move.
