Ceratosoma amoena - unusual shape & behaviour

January 10, 2001
From: Des Paroz


Dear Bill
As I mentioned in the last posting (about Chromodoris daphne), I have made a few dives a Shiprock [Port Hacking, Sydney] lately. On the one before last (30 Dec 200), I noted towards the end of the dive some kelp with several Ceratosoma amoena specimens high up (in the "fronds"). This was on kelp on a sandy bottom in the shallows, at the end of the dive. Of course, having taken a bunch of photos of C. daphne, I had no film left.

I went back on the high tide on 4 Jan 2001(about 4pm), and saved some film. Again I found three individuals doing the same thing, and got the photos attached. As I have learnt, nudis are carnivores, so they can't be eating, so I wonder if there is a simple or known explanation for this behaviour.

These photos are also interesting because the specimen I chose seems to have a deformity on the right rhinopore. Instead of being a single feeler, this one appears to have three arms, shaped like a trident.

Not sure if this is anything unusual, but thought you might be interested in these shots.

Best regards
Des

des@paroz.com

Paroz, D., 2001 (Jan 10) Ceratosoma amoena - unusual shape & behaviour. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3499

Dear Des,
Always happy to see nice photos of nudibranchs doing interesting things. Firstly the trident shaped rhinophore is indeed unusual, and clearly a birth defect.

About the behaviour of crawling up the kelp. Some species seem to be 'wanderers' and others do not. C. amoena and Hypselodoris bennetti are two chromodorids that are often found crawling far from any obvious food. Around Sydney, in the shallow sublittoral, both these animals and another dorid, the bright red Rostanga arbutus can often be found crawling on kelp plants, especially as the tide is beginning to rise after low tide. These animals all feed on sponges which are not associated with kelp. All I can assume is that they have either ended up on the kelp by accident as they crawl around, or they have been dislodged during tidal movement and have ended up on the kelp by being 'filtered' out of the water as they ave floated past. I may be quite wrong but I have always assumed the presence on kelp is accidental.

If anyone has other ideas or observations I would like to hear of them.

Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Jan 10). Comment on Ceratosoma amoena - unusual shape & behaviour by Des Paroz. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3499

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