TBS Founder, “The “trunk” emerging from the head of this snail likely identifies it as a whelk. Unfortunately, whelks often bore through barnacles and other crustacean shells, so you may want to get rid of it if you happen to find one.
Occasionally a small snail will stow away on our live rock. Some good guys and some not. Beautiful shell? Could be a predator Tulip that has a taste for clams. Armored shell? Could be a predator Murex. Tiny shell emerging from the sand bed could be a friendly nassarius.
The snails you want to keep are easily satisfied with the regular algae that accumulates on tank walls and live rock. Whelks and other unwanted snails make great escargot for a predator fish.