yes.....coral!is there something on it's shell. (bottom right)
I also hear that clams shouldn't go into tanks that are less than 1 year old. is that true?
i think you will be fine if you add a dersa clam to start.
list of clams to care for from most easy to hardest,
1.dersa
2. hippopus
3.gigas
4.crocea
5.squamosa
6.maxima