 Many of them (such as "Oxynoticeras") are thought to have been good swimmers, with flattened, discus-shaped, streamlined shells, although some ammonoids were less effective swimmers and were likely to have been slow-swimming bottom-dwellers.Synchrotron analysis of an aptychophoran ammonite revealed remains of isopod and mollusc larvae in its buccal cavity, indicating at least this kind of ammonite fed on plankton.They may have avoided predation by squirting ink, much like modern cephalopods; ink is occasionally preserved in fossil specimens.