December 11, 2007
From: Georgina Jones
A friend of mine found a pair of Phyllodesmium horridum in a rock pool, one of which we think may be in the act of laying eggs -- would the eggs be laid from a sort of ovipositor as sown or is this just an artefact of the picture?
Locality: Smitswinkel Bay, 5 m, Western Cape, South Africa, False Bay, Indian Ocean, October 2007, rock pool low tide. Length: 4cm. Photographer: Geoff Spiby.
Jones G. J., 2007 (Dec 11) Phyllodesmium horridum -egg laying?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21224
The egg ribbon could possibly be that of Phyllodesmium but its a bit hard in your photos to see enough detail to know if it is a nudibranch egg ribbon or not. Concerning the possible ovipositor it is in fact the elongate tip of the tail - or more correctly the posterior tip of the foot. Some species of Phyllodesmium have quite an extended 'tail' like this which produces quite a sticky mucus. I presume for animals living in quite high current areas its a helpful way to stay attached to your food source. It is possible the tip of the foot is used in manipulating the egg ribbon as it is being deposited, but that presupposes that the eggs are the nudibranchs, and I can't be sure they are.
There is another interesting subject in your photo. Scattered around are small red patches of some cnidarian, presumably an octocoral of some sort. In the photomontage alongside, I show three parts of your photo in more detail. In A, softcoral animals [the polyps] are fully extended while in C, they are fully retracted. In the middle photo [B] I am pretty sure the nudibranch is feeding on the colony and the polyps are semi-retracted. You will see the red colour in the digestive gland ducts of the cerata matches the red of the soft coral very well.Gosliner reports that this species feeds on the gorgonian Melitodes. On first sight this doesn't look very gorgonian-like to me but I don't know anything about Sth African cnidarians. If anyone can identify the cnidarian in these photos it would be a useful contribution