Amusingly, English has imported most of its words for specific shapes of pasta from Italian, where they are plural countable nouns - but because English speakers don't generally recognise the Italian plural forms as plural, we treat them as uncountable nouns. If we were being pedantic, we could decide to talk about one spaghetto, one tagliatella, one raviolo, as opposed to several spaghetti, several tagliatelle, several ravioli, but we don't :-)