To continue the hints of diePrinzessin:
Un păianjen este un animal din ordinul arahnidelor.
Is there a pronunciation difference between "paianjen" and "paianjeni", as the i sounds like it's always silent on these plurals? Thank you
Yes, there is a short i pronounced for the plural form. It us hardly audible even in real life for natives, but one can figure out from the context...
un păianjen, doi păianjeni
I heard păianjen