LTA
 

Does an LTA absolutely need a 4 inch deep sand bed, or is there another suitable substrate ?

I only have 1.5-2" and mine is fine. It has backed itself up to a rock face, where it seems to be happy.I anchored itself under a rock.

The reason that these are found with their foot buried in sediment (Bob Fenner at wetwebmedia) is that they need the depth to retract completely into it.

Mine has disappeared a couple of times. I don't think that 2" is enough for this animal, ideally. (Should mention though that mine is also backed up against a large rock.)