REPLY: Dear Richard,
what an interesting little critter and congratulations to Mr. Alex. I have never ever seen this species before and thank you for taking the time to send it to me. This is how the knowledge of the World of Water is increased.
COMMON NAME: DIDEMNUM LAMELLARID
SCIENTIFIC NAME: Lamellaria sp.
REMARKS: Lamellarids are very strange little molluscs which mimic encrusting ascidians upon which they feed, and as such are extraordinarily difficult to find. I have no idea what this one was doing crawling along on a sea cucumber, except that as sea cucumbers move very slowly and Lamellarids have no eyes. Perhaps this one was looking for a new host and crawled over the sea cucumber much the same as it would the bottom. Or it moved up off the bottom to smell the current for a trace of which way it should go for dinner.
I have a number of species of Lamellarids featured in my book 2002 SEA SHELLS and have illustrated for the first time a number of undescribed species. It would appear that Mr. Alex's specimen is another undescribed species. Now you guys will have to find the ascidian it lives on and see if you can find more.
Best wishes Neville