Clams are bivalves. They have an inhalant and exhalent siphon. The inhalant is the side with just a slit and some smallish tentacle looking appendages (used to reject large particulate matter). The exhalent looks more like the "clam neck" that you are used to seeing on steamers and other food clams. The bivalve takes water and food in through the inhalant, and expels through the "male looking" exhalent.
Derasa & Squamosa are more tolerant of low light situations and do well on the sand bed. Don't move them around much. They will adjust to conditions or squirm their way into a better one. If you move them around, you'll stress them out.
Croceas ARE boring clams. They like to attach to rock. This is why their shell is more polished and smoother than maxima and squamosa. If you are not sure where you want to place it just yet, then put just a small flat piece of rock under it. Either that, or use a clam shell. I used scallop shells because you can clip them back easily once they attach. If you put them on your reef, on LR, consider that placement the LAST placement because within hours, you may not be able to move them without tearing the byssal gland. This most often leads to the demise of the clam.
Maxima will also adhere to LR and being as light hungry as they are, should be placed up on the reef unless you have 250's or something. They don't bore like the croceas do (easily observed by exaggerated scutes) but appreciate attachment via byssus threads. Even if you keep them on the sand, you should let them attach to a shell or flat stone.
I would seriously con cider letting maxima and crocea attach to something. Especially crocea. They have a much larger byssal port than other tridacna. They are vulnerable to attack through that gland from predatory worms, crustaceans etc.
I have three crocea and one squamosa in a 75G under dual 175 MH and 2 actinic tubes. The crocea are more demanding of light and are "boring" clams. Therefore, I have them on the Live Rock, up higher on the reef. The squamosa is on the sand bed.
Get Knopp's Giant Clams book for a good read.
David
