In the shell of this green abalone, a large sea snail, the difference between the inner and outer shell is stark. The shimmering inside of the abalone is known as the mother of pearl.

It’s the shell of the knobbed whelk, a large sea snail common in coastal waters along the state’s seashore. Its beautiful, spiraled shell is a familiar sight on barrier island beaches.

Whelk sea shells get this stained look after being buried for extended periods in marsh mud. The resurface on beaches after the mud shifts closer to the sufact, says the National Park Service ...