What is Philinopsis cyanea doing?

August 6, 2008
From: Valda Fraser

Dear Bill
I found a pool on a wide beach that had been caused by high seas. Unfortunately the pool was in the process of drying out. On the edges of the water, Philinopsis cyanea (maybe a dozen of them) were creating these sacs - perhaps to lay eggs in before they died. What do you think?

Locality: Pomene, 20 cm, Mozambique, Indian, 15 February 2008, Pool on beach. Length: 70 mm. Photographer: Valda Fraser.

Best wishes
Valda

valdafraser@mweb.co.za

Fraser, V.J., 2008 (Aug 6) What is Philinopsis cyanea doing?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21769

Dear Valda,

If you look at the close-ups I have included, you will see that the sacs are in fact filled with strings of small white eggs. Aglajids have this strange way of putting their eggs in the egg sac by wrapping the egg string around their head and then gradually 'pushing' the string and the egg sac enclosing it off the front of the head. Your photo illustrates the process rather well. 

I am not quite sure of your description of the pool the aglajids are in. Do you mean it is above the usual high tide level and so when it dries out that is the end for Philinopsis, or is it likely to fill up again at the next high tide? In either case, it is interesting how many sea slugs start egg laying when they are in dire straits. Often when you collect them they will lay eggs in dishes, bottles etc, almost as though they know their end is near and this is their last chance to pass on their genes. Interestingly often the 'egg string' contains no eggs, sometimes just a ribbon of yolk, and sometimes the eggs are unfertilised. These 'mistakes' would suggest to me that going through the motions of egg-laying is an innate response to stress. Certainly it is not a bad response, because if the animals do have fertilised eggs it is better to have them out than in, and if the animal is about to die it really doesn't matter about the 'mistakes'.

Best wishes,
Bill Rudman

Rudman, W.B., 2008 (Aug 6). Comment on What is Philinopsis cyanea doing? by Valda Fraser. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21769

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