LeaLupin-Here's an excerpt from Deathly Hallows. "When the patronuses glided out of the dungeon there were cries of shock from the people waiting outside."

And, here's one from Order of the Phoenix "The few patronuses people had managed to conjure faded away into silver mist..."

The books always use "patronuses" as the plural.

He won't have one because he doesn't have any happy memories

I think it was a snake for the main reason his most prized possession was nagini and modeled his image after a snake

although he doesnt have one, nagini or a basilisk

Even though he doesn't have one because he doesn't have happy memories of he did it would be a snake

I looked it up and jkr said that he didn't have one bc he doesn't have any happy memories but if did have one it would be a snake

His soul was split into 7, depriving him of happiness or love. Those things are vital to conjuring a Patronus, so he has none. There is even evidence, I read it somewhere, but unfortunately, I don't remember the website.

Lmao, true! Never thought about it! ;D

A Serpent after all he was evil, sly and the heir of salazar slytherin(my theory)

He didn't as he was on the side of what patronuses where trying to destroy. This made him incapable of casting a patronus.