Northwest Dive Club

I saw this marine mollusk while snorkeling at Richmond Beach this summer.
Does anyone know what it is?

Hi. Kind of hard to tell. Do any of the mollusks on these pages look similar?
http://emeralddiving.com/id_bivalves.html
http://emeralddiving.com/id_snails.html

Is there a visible shell? Watching the video (from the other thread) it flies by so fast (has the video been run through a stabalizer?) that it is really hard to tell, but I thought I saw movement along the body of it... and it is rather over-exposed so it is losing all the detail.... but I honestly wondered if it might be a White Lined Dirona nudibranch.

Answer to both replies. Thank You for trying. There is definitely a shell, and there is a spike sticking out of it. None of these mollusks from emerald diving have the distinctive white shell that this critter has. Looks like I'll have to be pest at the Oceanography/Marine Biology school. It's fairly uncommon and I don't have good picture.

Could it be a moon snail? They have a shell that can look different depending on how retracted the body is, and they have what can look sometimes like a spike coming out of them. See the picture on the very far top right of http://emeralddiving.com/id_snails.html

Well I would say that's a moon snail even though it's completely blown out and looking white ...

Update: I think it's a piece of the shell of a dead mollusk. Someone at the shell club thought it was a Leafy Hornmouth.
The spike is the identifier. Anyone got an idea?

Looks a bit white, big and shallow for a leafy hornmouth but could be.