With more than 900 known species, cone snails are among the most diverse sea snails on Earth. Their highly patterned shells are irresistible to shell collectors, who often think they’re harmless souvenirs washed in by the tide. Some are streaked with caramel-brown coloured zigzags, while others are covered in delicate dots, stripes or net-like markings that resemble fine porcelain. Seashells expert guide: what are they, where do they come from, and how are they made?