Images from an upcoming official announcement video have leaked online. These all appear to be legit but are not 100% confirmed.
The fish with the school form is known as Wishiwashi and is Water type with the ability Schooling. The sea cucumber is called Pyukumuku and is Water type with the ability Innards Out. There is a new mushroom Pokémon called Morelull which is Grass/Fairy type. And Raichu appears to have a new Alolan Form: it's Electric/Psychic and has a new ability Surge Surfer.
We'll bring more details when we can. Here are the leaked images:
Wishiwashi Solo Form