I remember the Dr Who episode with those beasties in it. Of all the horrors that Davros was supposed to have created in his experiments, the Doctors companions end up being attacked by Giant Clams. Are the shells real? Or have they been cast from real? Nice way to get animals into your Dalek theme Westphalia Chris.
They're actual seashells from a 'Poundland' equivalent. I matched clockwise and anti-clockwise shells and affixed them with superglue. It's surprisingly hard to find actual "animals" in the Whoniverse (budget restrictions, apparently), and I couldn't find suitable donor models for either Magnedons or Terrorkons in time, so mutant molluscs and a Slyther it was.