Re: Two Halgerda species mating

April 10, 2003
From: Atsushi Ono

Dear Bill,
Concerning your question about whether the Halgerda were actually mating. Unfortunately I didn't touch their mantle edges - if the mating continued, I
was going to take a photo with my camera. After 40 minutes these 2 Halgerda had separated. But I believe I can see a part of the genital organs which have scattered dark brown dots. And also the mantle margin above the genital organs swelled out a lot. This was easily visible when I found these 2 Halgerda in the sea - now God knows the truth.

Atsushi Ono

Ono, A., 2003 (Apr 10) Re: Two Halgerda species mating. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks very much Atsushi,
I am sure you saw them mating - its just that scientists like to see something with their own eyes, especially when it is very unusual. Species of Halgerda have these brown-black spots on the inside skin of both the genital opening and the oral tube so when you see them its a good sign that the relevant organ - in this case the genital organs - are everted. It is indeed an interesting observation.
Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Apr 10). Comment on Re: Two Halgerda species mating by Atsushi Ono. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Halgerda diaphana

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