All reef aquarists are familiar with the beautiful tridacnid clams found in the shallow waters of coral reefs throughout the Pacific. Daniel Knop has a column devoted to them in this magazine and has discussed them in some detail. Tridacnids, however, are very unusual clams. They have symbiotic zooxanthellae and they also have an odd orientation to their internal anatomy relative to their shells. In this column, I will discuss some aspects of basic clam biology and some of the other species that are occasionally available in the aquarium trade.
