found this at exotictropicalsspotcom.....
"Placing your T. maxima in your tank is pretty much the same as placing your T. crocea. Pay attention to the color of the clam's mantle and use that as your judge for where your clam should go. Some T. maxima's will show vivid coloration and others will be showing off the brown color of their zooxanthellae. If your clam's color is iridescent, it has adapted to bright lighting and should be placed closer to the top of your tank. If your clam is mainly brown, it should be placed lower in your tank away from strong lighting.
If you have a healthy specimen, it will attach itself to the substrate in less than a day. Keep this in mind when placing your clam in the tank. Make sure you put it where you want it to stay."
derasa clams can be placed just about anywhere, they loose their byssus gland after awhile.
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