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.
How does Two-Factor Authentication work? When you sign into your account, you will be prompted to authenticate with your user name and password. This becomes your first authentication factor. For the second authentication factor, you can use a One-Time Password (OTP) token, an SMS sent to your mobile phone, a USB or key fob (e.g. something you have).