Hose Eggs thats what we called them in Newfoundland when I was a kid.

Purple sea urchins thrown upon the landwash from the darkened deep.

Hey, I found this really awesome Etsy listing at https://www.etsy.com/listing/193756378/terrariumair-plant-hanger-standpurple

Tillandsia bulbosa air plant nestled inside a purple sea urchin, together they hang gently from a silver hanger.