Catullus/A Bark's Dedication

What I found unusual in Catullus' "A Bark's Dedication" poem was the fact that he says, "Gemelle Castor and gemelle Castoris." Why would Catullus use diminutives for the deity patrons of mariners? Catullus, after all, sailed safely home from Bithynia; so, I think that he should have praised the Castor and Pollux for possibly helping him. Though these twins are also part mortal. Perhaps Catullus used diminutives because of the twins' lack of complete divinity. Or, Catullus was more absorbed with appreciating items of a concrete world, such as a ship, than religious pietas. What do you think?