Wow! interesting. I'm suprised you don't feed it whole clams (cheap from Publix). Here's some info for those that may be considering adopting this critter:
"They consume bivalves (invertebrates with two shells), especially oysters, clams, and scallops, as the mainstay of their diet...
The carnivorous habits of the whelks begin as hatchlings. The whelks that hatch feed on the eggs that did not hatch. When feeding, an adult whelk will try to pry open a bivalve by inserting the edge of its shell inside the bivalve and using it like a crowbar. If it cannot pry the bivalve's shell open this way, it will grind the shell with its own shell until it creates a hole large enough to insert its radula (toothed tongue). The lightning whelk can "smell" its prey with special sensory organs inside its body and will almost completely bury itself searching for other food. "