I pulled this shell out of grit collected at Turtle Beach, Oahu (21.617541; -158.086566). It looks most like very early stage Coralliophila fimbriata but I can't find any images of Coralliophila larval shells/protoconchs to compare it with. I also considered Phenacolepas but images I see of their protoconchs don't seem to match. I'm amazed at the change in shape from one stage to the next. The specimen is about 1-2 mm in diameter. Any help would be appreciated.