If it's a real conch, it will eat micro- and macroalgae, as well as the epiphytic organisms that live on the algae. If it is a true conch, it will have a "strombid notch" on the lip near the opening end, and the eyes will look like they have pupils like human eyes. It will also have a long, skinny, pointed operculum that won't close off the entire shell.
Cheers,
Don