Then I would check to see if you have Pyramidellid snails.
Barry Neigut
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Inspect the clam around the mantle and “byssus” (foot) to make sure there are no Pyramidellid (“Pyram”) snails. These parasitic snails can do serious damage to the clam and must not be allowed into your aquarium. Make sure that you carefully examine the specimen for the presence of jelly-like sacks which house the eggs of these snails. Several dozen snails can hatch simultaneously. If Pyramidellids are discovered in your aquarium, there are a few fish that will help in controlling them, such as Coris formosa, Coris gaimard, and the popular Sixline Wrasse, Pseudocheilinus hexataenia. Manually removing these pests at night (when they are feeding) may also be necessary
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