Not a linguist, but I agree with Alienvoord.
Moreover, also in Sardinian (a language spoken in a particular region of Italy, considered to be one of the few still-spoken language closest to Latin) the plural is formed by adding -s, both for masculine and feminine nouns (and adjectives, too):
Manu, manus (hand, hands; M);
Domu, domus (house, houses; F)
Mannu, mannus (big: singular and plural form; M)
Manna, mannas (big: singular and plural form; F).