I took it upon myself to count up all the different species of monsters, and here's what I found:
The first category is monsters with known names that have gotten a good amount of focus in the game, of which there are 9: Asura, Gestas, Gorgon, Hexenringe, Himavat, Hrungir, Leigong, Minyak, Rebis
The second category is monsters that have a decent amount of story focus, but do not have names atm, of which there are 14:
The glowing blue monster that Alice's dad has, the monster that the scared H.E.R.O. agent was running from, Angelina's monster, The blob monster we help Del kill, the 2 monsters that Deryl's Chimera's used as back up, the crystal monster we helped Demi and Angelina catch, the monster that Alice and Laurie fought, the 2 monsters from the memories in the shopkeepers items, the sea serpent that we killed for Clark, Demi's monster, the water monster that we killed with Laurie and the monster that crashed Tiffany's wedding
The third category is monsters that have been named but haven't shown up yet, of which there are 4: Luz Mala, Orang Minyak, Giest, M:39
The fourth category is superhumans and chimeras who have powers that are completly unlike any monster we've seen so far, of which there are 28: Alexis, Bernhardt, Briar, Charlie, Clark, Cole, Duncan, Henri, Jared, Jill, Laurie, Lucius, Malik, Melody, Nyx, Po, Sharon, Shen, Troy, Zara, 2 1st chimera powers, 2 2nd chimera powers, 1 3rd chimera powers, 2 H.E.R.O. agents, 3 S.I.N Members
And then finally we have monsters that simply appeared in the background with no focus whatsoever. I scoured the games image folders and counted about 24, though this could be off some what. It won't let me post them for some reason, but the image names are "elinv26", "elinv35","elinv50", "elinv63", "elinv73", "ellamon13", "langdon82" and "Nico8" in the games background folder if you want to check them out.
So all in all that equals 79 monsters so far.