Mystery dorid from Leigh, New Zealand

Dear Ian,
At that size I suspect they are juveniles. You don't mention whether their backs are smooth, spiculate, warty, or otherwise sculptured. On the basis that they are smooth, my guess would be they are juvenile Aphelodoris luctuosa which is one of the commonest subtidal dorids in that part of New Zealand. As that species grows to about 80mm, your animals would lack some of the finer details if they are indeed juveniles.

A large cluster of juveniles like this is often an indication of a species with non-planktonic larvae, juveniles benthic slugs hatching directly from their egg mass. As far as I know the development strategy of Aphelodoris luctuosa has never been reported so that is not much help. I assume you are at the Marine Lab at Leigh. If so, perhaps you should try to keep the animals alive on the sponge for a while and see if they will grow to a more identifiable size. If you can take a photo that might help me to identify them.

The reference you mention:
• Willan, R. & Morton, J. (1984) Marine Molluscs. Part 2. Opisthobranchia. Leigh Marine Laboratory, University of Auckland, New Zealand.

is the most useful reference. The fauna is not that large as to makea key necessary.

Sorry I can't be more help,
Best wishes,
Bill Rudman