C for clam; c for confusion

[mrhasan]

Clams have always confused me BIG TIME! Some say they are easy to keep, some say they are hard to keep, some say they need pristine water while I found that clams sucks up nitrate. Few days ago, I came to know that they can move :S

Now I have a very tight spot in my tank for a clam since I have always wanted one. But this movement can be a big issue!

So can anyone illuminate on this clam moving around issue? Is there any clam that has the reputation of moving lesser than others? Lighting shouldn't be any issue since I will be getting a quad T5HO fixture soon (on its way from USA).