Siphopteron flavum mating from Japan.

May 10, 2003
From: Jun Imamoto

Dear Bill.
Fortunately I have recently observed mating in Siphopteron flavum. Each phallus appears to come out from the side of the visceral lump. Then it is inserted around the bottom part of the partner's head.

I have also sent you a photo of a yellow individual which wasn't copulating. As usual, both the yellow and orange types were found together. I am happy if these reports are useful for your research.

Futou, Izu Peninsula, Suruga Bay, Japan. Size: approx 4mm, Depth: 2m, Temp:19 C. 3 May 2003.

Best Regards,
Jun Imamoto

Dear Jun,
Thanks for these interesting photos. I don't know of any published information on mating in gastropterids. I think what is happening is the penis is coming out of the side of the head [see your lower right photo] and inserting in the female opening, which is on the right side of the body.

In most cephalaspideans the penis is physically separated from the rest of the reproductive system. The 'female' part of the reproductive system opens in the mantle cavity, or in cases like Siphopteron, where the mantle cavity is almost completely gone, it opens on the right side, where the last remains of the mantle cavity are found. In cephalaspids, and the anaspids [Sea Hares] there is an external groove from the female genital opening, which runs forward along the right side of the 'neck' to the opening to the penial sac on the right side of the head. The penis, prostate, and associated glands lie in this sac, inside the body except during mating, when the necessary parts are everted. The groove from the female opening carries the animal's sperm forward to the penis. During mating the penis is everted and inserted in the partner's female genital opening in the mantle cavity or on the right side of the body.

I would suspect what is happening in your photos is the penis everted from the right side of the head and is inserted in the female opening on the right side of the partners body below the visceral hump. It seems that part of the female system everts partially as well. In your upper photo the penial apparatus is narrow near the head and very wide near the other animal's visceral hump. You would expect it perhaps to taper the other way around, with the thin bit near the tip. However as Terry Gosliner's (1989) review shows, the penial complex in Siphopteron is quite complicated. As well as a tapering penial papilla there is an accsessory organ armed with spines. In fact he named one species S. quadrispinosum after the impressive set of 4 large spines it possesses. If I'm right I think the bits you can see in your photo are the female opening [fo],
and through the transparent wall of the penial sac, the muscular accessory organ with penial spines [ps]; the prostate gland [pr]; and either part of the penial papilla, or the sperm groove [pp].

Best wishes,
Bill Rudman

Rudman, W.B., 2003 (May 10). Comment on Siphopteron flavum mating from Japan. by Jun Imamoto. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Siphopteron flavum

Related messages

  1. Re: Siphopteron flavum feeding?
    From: Ayumi Murakami, October 31, 2006
  2. Siphopteron flavum feeding?
    From: Ayumi Murakami, September 8, 2006
  3. Re: Siphopteron flavum mating from Japan
    From: Jun Imamoto, May 12, 2003
  4. Siphopteron flavum - colour variation
    From: Jun Imamoto, May 10, 2003
  5. Siphopteron flavum from Izu Peninsula, Japan
    From: Haruo Kinoshita, August 15, 2002
  6. Siphopteron flavum from Japan
    From: Nishina Masayoshi, August 4, 2001
  7. Siphopteron flavum? from Japan
    From: Yasuhiro Shirai, March 1, 2000
  8. Siphopteron flavum from Kerama Island
    From: Atsushi Ono, July 30, 1999

Show factsheet and all related messages