Tritoniopsis elegans and camouflage

October 18, 2001
From: Nishina Masayoshi

Dear Dr.Rudman,
I have observed the ecology of the various sea slugs in the sea before but I was really surprised at this observation. I could find what I thought at first was one sea slug [Tritoniopsis elegans when I turned over a stone (LOWER RIGHT). But, my wife noticed that gills apparently grew from that animal's foot as well (LOWER LEFT).

So I tried to remove the big sea slug from the stone because it seemed very strange for it to have gills on its foot. Then, five little sea slugs moved out from under that animal. Five little sea slugs were hiding under the foot or beside the foot of the big sea slug. It was an unbelievable sight (UPPER RIGHT PHOTO).

I sometimes see groups of the same sea slugs together but they are usually of the same size. Meanwhile, the big sea slug began to move to the end of the stone, and when it stopped one of the small ones followed it like a child following its parents. I realise that these animals don't provide 'childcare' and probably the large one isn't a parent of the small ones but it certainly gave that impression. Then, What does this mean? Are they only just hiding or are they clustered together for camouflage in a place where they look like the soft corals? I see that Bernard Picton has already sent a similar photo of T. elegans to Forum before. I wonder if the juveniles in his photo were hidden under the adult? or whether they were just close together?

Data:
Date:14 Oct, 2001
Location: Fukuura Port, Sagami Bay Japan
Length: Biggest one 50mm-60mm
Small sea slugs 10mm to 20mm

Best Regards,
Nishina Masayoshi

nishina@wips.co.jp

Masayoshi, N., 2001 (Oct 18) Tritoniopsis elegans and camouflage. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5486

Dear Nishina,
What an interesting observation. I think the basic reason they are all together is that their food is nearby. I guess they were eating the colony which we can see broken off in your upper photo. Many sea slugs which eat massive colonies of soft corals and hard corals, cluster around the base of the colony, especially when they are juveniles, and in the case of hard corals like often underneath them.

I suspect that when large animals and small ones are together, the larger ones can crawl over the small ones like in your example. When they are very small their natural defence seems to be to hide, but as they grow larger and begin to look much like their food, they spend less time 'hiding' in crevices and under things, and begin to sit out in the open on their food, apparently relying on their camouflage to protect them.
Best wishes,
Bill.

Rudman, W.B., 2001 (Oct 18). Comment on Tritoniopsis elegans and camouflage by Nishina Masayoshi. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5486

Factsheet

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