After Crawler is Gray Ooze. I think I fought some of those in the past Temple of Chaos, but I'm not sure where or on which floor. It could have been the Floating Castle too. I seem to recall running into several groups of them though, wherever they were. After the Desert Baretta is the Sabretooth. I don't remember where I ran into him. The rest of them are a mystery to me as well, although I just found something on GameFaqs.com that looks fairly helpful:

http://www.gamefaqs.com/console/psx/game/33791.html

check out the "100% Omake Guide" under in-depth faqs. I don't know what an omake is, but it looks like it has a list of monsters in the collection bestiary and where to fight them. Hope this helps.