Hello Anne, in reply to your son's question, Knobbed Whelks can grow up to 9 inches in length. Channeled Whelks top off around 8 inches. They represent the east coast's largest gastropods (snails). They (and their eggs cases) are also fairly common around Cape Cod where I collect them. I have from time to time snorkeled in shallow water and found the large females depositing the egg cases in the sand (always a remarkable sight).