Something is curled if it goes around in a series of loops, either in a helix or a spiral. The curls in the picture are more of a helix, wheras a fern frond uncurling is more of a spiral.
Mother of pearl is a very hard, attractive substance that is is frequently used in jewellery or as inlays on furniture, wooden boxes or even the handles of guns. Mother of pearl, or nacre, is the iridescent material lining the shells of some sea molluscs, which includes snails, clams and other shellfish. Most commonly, mother of pearl was used for centuries to make buttons from.
Pearls are made inside the shells of mollusks like clams and oysters. They are usually round, and have a soft, translucent glow to them. Pearls have been made into jewellery for thousands of years.