Yep.
And well, here's BladeRunner's interpretation of the summons:
I agree with most of them, except the one that says Siren, who I actually think is Leviathan (FF's Siren has never been the usual interpretation of a mermaid and is rather the half bird, half woman one (that was, iirc, the one that existed before)).
While the serpent, I think, is a lesser being (like all the other suffering individuals, like Ultros). Also, I actually have the totally stupid theory that Gentiana is Leviathan's human form. Don't laugh.
Ah, hopefully we get NEW summons this game. One of the things I actually loved about X were the new ones. Ramuh is great and all that, but man, I adore Ixion. And Valefor and Anima too!
PS: I wish we could get a mainline FF that looked just like that painting. Love the classical look, it might as well be a real life mythological-based painting.