I doubt your lighting is good enough for clams, but, if you must, I would recommend a deresa 1st, at about 3 to 4". not as colorful as the others but cheaper and will give you a chance to see if you can keep one alive. if you must contain cost you could do a 2" but the smaller ones are harder to deal with. 1st though, I would recommend a good book before jumping in. one that i have and is a very good reference is GIANT CLAMS (A comprehensive guide to the identification and care of tridacnid clams) by: Daniel Knop - ISBN 3-921684-23-4. The book is a bit pricey (about the cost of a clam) but well worth the investment if you want to be successful with clams. good luck.