I left the reef early in the interest of keeping my SLR dry, and was chilling in my car when Jeff tapped on my window to show me this: the pseudoconch of the sea butterfly Corolla spectabilis. Sea butterflies are very strange pelagic mollusks that have wing-like mantle flaps. This particular one grows this gelatinous "pseudoconch" instead of a shell, and sometimes they wash up on beaches. How awesome is that?

Note: about 95% sure this is C. spectabilis. Comment if you can confirm.