the cowrie is a 'snake's head cowrie' i think....my book says they grow to 3cm(so much smaller than the tiger cowries), and says they live on coral reefs. (they may eat them tho...it doesn't say!)
the other looks a lot like a 'drupe'(family....'muricidae')...also growing to 3 cm....as my book is about shells it doesn't say what they eat....just that they live on intertidal reefs!
can't help you with the fish i'm afraid
nick