Where do nudibranchs sleep?

January 25, 2002
From: Jeanette McInnes

Dear Dr Rudman,
On a recent trip to Osprey Reef, Coral Sea, it occurred to me that I've only seen nudibranchs out after dark approx. 3 times (Ardeadoris egretta, Glossodoris electra) and asked myself, "Where do 'branchs go to sleep?"

In a bid to save you the pain of answering the same question dozens of times, I searched the sea slug forum for this info... in vain. If I missed it somewhere, then I apologise! Is it possible that some nudibranchs are noctural? Do they keep to a strict timetable like many tropical marine animals? Is it just a coincidence that 2 insomniacs that I've seen are both white? Since they're smelly & poisonous, why don't they camp out in the open like the inedible pufferfish? I'd be interested in any other sleep-related info on our friends.
Love the Slug Forum!


McInnes, J., 2002 (Jan 25) Where do nudibranchs sleep?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/6054

Dear Jeanette,
We still have a lot to learn about activity cycles in sea slugs. There is some information scattered throughout the Forum but I haven't as yet prepared a specific page on the topic. The general feeling about tropical nudibranchs is the reverse of your suggestion. During the day it is thought that only phyllidiids are distasteful enough to blatantly expose themselves while other nudibranchs are hiding under rocks, in crevices, or asleep. The very nasty chemicals that phyllidiids have in their skin are considered so distasteful to fish that they are avoided.

Another group of colourful nudibranchs, the chromodorids, also have nasty chemicals in their skin to deter predators. In both tropical and temperate waters, some species of this family are often out during the day, often in groups. These species usually have a colour pattern which is very similar to that of a group of other species. Have a look at the page on Red Spotted species to see why we think groups of species share similar colour patterns.

Many other nudibranchs are so well camouflaged, or so small, that they are usually overlooked by all but the most fanatical or experienced nudibranch hunter. Also many sponge-feeding dorids eat species of sponges which prefer shaded places and crevices so the nudibranch, even if active during the day, is not very visible. In general we can say that some species have developed protective strategies to allow them to out and about during the day, others have not. There doesn't seem to be any simple rule. Have a look at the page on Defence for some more information.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Jan 25). Comment on Where do nudibranchs sleep? by Jeanette McInnes. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/6054


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