Nembrotha rutilans laying eggs - some more details

June 24, 2005
From: Roberto Sozzani

Note added 4 March 2008: Following Pola et al (2008) the name N. rutilans has been replaced by Nembrotha purpureolineata [see message #21419].

Dear Bill,
In your message #13678 you said: "What I am not clear about is where the eggs are extruded. It is possible there is a third opening?"

I found this photo which, maybe, can help to give an answer to your question. It shows an organ extruding eggs. It looks like it is the sexual organ (it has the same position), modified in shape, so that eggs are extruded already as a ribbon. The opening has a height of about 10mm. (near the right rhinophore there is a parasite which has a normal size of 4-5mm. and the opening is about twice that size).

From the photo it's not clear if this could be a third opening or the vagina enlarged for this purpose, but I'm not an expert. I hope this photo can give you some clues about your question.

Locality: Rinja Island, Indonesia. Depth: 12 metres. Length: 7 cm. June 2003
Healthy reef. Photographer: Roberto Sozzani

Best wishes,
Roberto Sozzani

Sozzani, R., 2005 (Jun 24) Nembrotha rutilans laying eggs - some more details. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Roberto,
Thanks very much. This does indeed answer my question. Most dorid nudibranchs have what we call a triaulic reproductive system in which the incoming and outgoing sperm, and outgoing egg ribbon all have separate ducts. Usually the incoming sperm and outgoing eggs share a 'female opening'. The openings are usually contained in a small genital pouch or vestibule which swells into a small mound during mating. I can't think of another group, other than these nembrothids, in which the vestibule has developed into such a large and elaborate organ. Because of this I wondered whether the egg-laying duct may have a separate opening at the base of this organ, something we could not necessarily see when dissecting a preserved animal in which this organ would not be expanded.

Your photo shows that the eggs also go right to the end of this mating organ as well, and the opening is greatly stretched to accommodate the wide egg ribbon.
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Jun 24). Comment on Nembrotha rutilans laying eggs - some more details by Roberto Sozzani. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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