Hey Cheerflip,
I personally don't think your tank could sustain a clam, esspecially with your current lighting. 20wts over a 50 gallon is hardly anything, which probably couldn't house a clam which is using its zooxanthellae. The larger clams get, the less they depend on using filter feeding. Clams around 3" or smaller seem to focus more on filter feeding than photosynthesis, and will need many regular feedings (I do not have any experience with filter feeding clams, therefor, someone else can chime in about that if they wish). I would wait off until you've upgraded to some better lighting before attempting any clam.
50 gallon salt water tank
20 watt 50/50 bulb
wet/dry filter
25 lbs live rock, 15 lbs base rock
crushed coral bottom
2 sebae clownfish
2 flame scallops
1 coral banded shrimp
2 cleaner shrimp
2 peppermint shrimp
2 emerald crabs
1 blue legged hermit crab
1 red legged hermit crab
10 baja hermit crabs
3 turbo snails
NM reef,
That's an exelent Squamosa clam! Very nice coloration!
Graham