Placida dendritica in northern New Zealand?

Dear Ruth,
You have certainly found a beautiful spot to work - and visit. When I was there many years a ago as a student, the lab was much more rudimentary.

Both the sacoglossans you mention feed mainly on an alga we used to know as Codium dichotomum, though I can't be certain that is still it species name. The important thing is that the alga, although usually intertidal, is usually found in crevices or under the brown alga Hormosira banksii [Venus's Necklace] - somewhere damp rather than immersed in a pool. Since its out of water at low tide, the sacoglossans are very difficult to see because they are lying flaccid on the algae. Often the first clue to their presence are their egg masses. The other way is to bring clumps of Codium back to the lab and cover them with sea water and watch for crawling slugs. I can't recall from memory whether the Codium is found on the rock platform at the lab, but it is certainly present in some of the nearby inlets and protected local shores. I am afraid you will need to get advice from local experts on the whereabouts of the Codium, because that is the key to finding the slugs. If you have not yet found this alga, there are some photos on the Fact Sheet and in some of the messages about this species. They are close-ups, but it is the only green algae you will see that looks like a branched finger sponge.

One word of caution however. Although both these slugs are relatively common, I'm afraid sea slugs are hopelessly unreliable. There is no guarantee that even the most common species will be there when you need it.

Good luck with your project,
Best wishes,
Bill Rudman