From live aquaria;
"Pyramid Snails
Identification
Pyramid Snails, or Pyrams are very small snails that belong to the Pyramidellidae family. They are generally white in color, have a slender shell that tapers to a point, and do not grow larger than a few millimeters. The Pyramid Snails use their long proboscis, which is a tube-like mouth, to puncture the mantle of a Tridacna Clam in order to feed upon the fluids and zooxanthellae cells contained within. A few snails will typically not pose a threat to a healthy Tridacna Clam. The snails reproduce every 90-120 days, and if left to multiply, can cause serious harm or even death to their host in a very short period of time.
Signs & Symptoms
Evidence of an inflicted clam can be noticed by poor expansion and loss of color within the mantle. The Pyramid Snails feed mostly during the nighttime hours. During the daytime, they will remain either at the base of the clam, or within the scutes of the shell, where they are difficult to spot. It is best to inspect an ailing clam with a flashlight a few hours after the lights have turned off on the aquarium. The small snails will line up at the top of the shell just below the clam's mantle.
Treatment
If you discover these snails, it is best to remove the clam to a separate container of aquarium water. Once out of the aquarium, you can physically remove the adult snails, and brush the entire shell with a new toothbrush in order to remove any eggs.
Natural predators of Pyramid snails include several species of wrasse within the genus of Halichoeres and Pseudocheilinus. A few of the more popular species that are reportedly very efficient at controlling these snails are; Six and Eight Lined Wrasse (P. hexataenia and P. octotaenia), and the Green Wrasse (H. chloropterus). "