Kukui Nut and shell necklace

Kukui Nut beads strung in a double stand with 3 closed shell accents. I'm really not sure what kind of shell they are, I've tried to look them up and can't find them. They're very pretty though with an iridescent sheen to them in the light. The necklace is 18 inches long with a lobster claw clasp and a 2 inch extender.