ok, after some quick research, it appears that the original paella recipe was just meats (chicken, rabbit, sausage) and veggies with rice, with snails added when available. it was invented in the fields and mountains near valencia, hence the common term paella valenciana.
the dish is a lot like chili in the united states where it was a worker's dish, so whatever ingredients that were available cheaply were added. the closer you got to the coast, the more likely it would be made out of fish and seafood.
somewhere along the line, people found they liked a mixture of meats and seafoods, so paella mixta was created and is the most popular version of paella worldwide.
in order to be more accurate, one would then order paella mariscos for all fish/shellfish, paella mixta for meats and fish, or paella vegetal for veggie paella.
there's also arroz negro which uses squid ink to turn the rice black.
man, i need some paella.