Easy clam for a newbie clamer ??

T. squamosa or derasa would probably do well, even on the sand bed/bottom (they don't need as much light). You could probably also do T. maxima or T.crocea, but you might have to move them higher up the liverock under the 175.

As far as movement goes...

I have a 4.5" squamosa that seems to have rotated. I placed it on my sandbed, oriented perpendicular to the front glass. Over the coarse of about two weeks, it rotated so that it's now parallel to the glass. Don't know if it moved by itself, or if other things moving on the sand bed (cucumber, serpent star) pushed it around.

This morning, I reached in my tank and turned my clam 90 degrees so that he was oriented perpendicular to the front glass again. Well, by this evening he had rotated back so that he was parallel to the glass. I guess I got me a stubborn one (maybe its really a she)!