Then you've got singular neuter nouns ending in -мя, like время, "time." There's an argument for calling such nouns a separate declension -- but then again, there are only TEN such nouns in the entire modern language
At least, I've always heard that there are ten of them -- but I couldn't list all ten if you held a gun to my head! Let's see, there's the words for "time," "name," "tribe," "burden," "flame," "banner," erm... "udder"... "stirrup," um...

Can't remember what the other two are, but supposedly, there's ten.