They belong to the Pustulate Cowry, an inch-long snail found in the eastern Pacific, from California down to Peru as well as Hawaii and the Galapagos Islands.
False cowries usually have pale, wonderfully smooth shells that can be completely covered by the flesh of their colourful mantles. Not so the Pustulates!
The mantle meanwhile, is far from the bright, multi-colours of so many other cowries. Instead, it's grey. It's attractive in its own way, though. The mantle is covered in long, branching sticky-out bits which are presumably sensitive to their surroundings.
Video: Eduardo Palacios
Pustulate Cowries spend the night nibbling on the polyps of various stone corals.
By morning they're hidden away, hopefully getting the medical care they need.