Roundworms have taken this last body plan and adapted to thousands of environments with it. From microscopic to maybe a meter long, roundworms are just what they sound like-round worms. At one end, they have a mouth, at the other, an anus, with a tube digestive system in between.
Availability of two-factor authentication for Apple ID Two-factor authentication is an extra layer of security for your Apple ID designed to ensure that you're the only person who can access your account, even if someone knows your password.
Although ID and password are two items, because they belong to the same authentication factor (knowledge), they are single factor authentication (SFA). It is really because of their low cost, ease of implementation and familiarity that passwords that have remained the most common form of SFA.