Re: Mating Cadlinella ornatissima from nthn Marianas

June 12, 2007
From: Yuji Fujie

Concerning message #19943:

Dear Dr. Bill,
I have found Cadlinella ornatissima again and took some more photos. Is the whitish structure from the upper animal maybe the vas deferens?
Would you tell me the actual name, please ?

Locality: Wing Beach, 6 m, Saipan, Northern Mariana Islands, Pacific Ocean, 28 May 2007, on the wall at shallow point. Length: 15 mm and 20 mm. Photographer: Yuji Fujie.

Best regards,

Yuji Fujie, 2007 (Jun 12) Re: Mating Cadlinella ornatissima from nthn Marianas. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Yuji,
The structure you are asking about is the penis of the upper animal. The vas deferens is the muscular internal duct through which sperm is moved from the 'male' part of the reproductive system of one partner to the 'female' part of the other partner. The penis is the 'papilla' or elongate structure which usually extends for the 'male' partner and inserts itself into the 'female' partner so that the sperm is transferred internally. If you look carefully in your second photo you can see a thin whitish duct running down the centre of the penis. This is the vas deferens.

You are probably wondering why the penis seems to be inserted into the yellow back of the lower slug, instead of into the female genital opening on the side of the body. I guess these animals don't always get it right. With hermaphrodite slugs both partners need to insert their penises simultaneously - or nearly simultaneously -  and sometimes, as in this case, one partner gets it wrong.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (Jun 12). Comment on Re: Mating Cadlinella ornatissima from nthn Marianas by Yuji Fujie. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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