AEAD without explicit authentication tag
As discussed in RFC 5116, AEAD is the tuple of encryption and decryption function: 


An encryption function that takes a key, a nonce, a plaintext and a header (associated data), and produce a ciphertext and a tag. 
A decryption function that takes a key, a nonce, a ciphertext, and a header, and produces either 1) the plaintext, or 2) decryption failure indication. 


The tag part you're concerned with is used to verify the decrypted plaintext (roughly speaking). 

However, there's a requirement that can sometimes be a pitfall in the real world: the nonce must be unique for most AEAD algorithms to be secure. So the clever people invented "deterministic authenticated encryption" (DAE in short, a.k.a. key-wrap in some contexts). These encryption algorithms advertise the property of "misuse-resistance". 
And AES-SIV is one such example.