Just a couple of thoughts in response to previous postings - First, on the question of whether a Xenophora attaches a sponge near its apex, or the sponge grows there on its own - A Xenophora cannot attach anything to its apex. Attachments are made at or near the lip of the shell as it grows, and then gradually "move" away from the lip (actually the lip moves away from the attachment) as the shell continues to grow. Those small attachments near the apex were put there when the shell was very small, and that was the location of the lip. On the matter of why one means of camouflage or disguise would be covered over by another - of course, the question of the purpose of Xenophora attachments is still open. Some people think it is for camouflage, others don't. But in any case, the additional growth of barnacles, tubeworms, bryozoans, sponges, or algae on top of the attachments is not due to any action of the mollusk. These kinds of growth are due entirely to the action of the secondary organism, and the Xenophora is simply a hard surface on which to get a foothold and grow. So it is really not accurate to speak of the Xenophora first covering itself with dead shells, and then covering itself with algae or other growths. The Xenophora creates the first covering - the algal or other species creates the second. Paul M.