Gastropteron chacmol mating?

August 30, 2005
From: Anne DuPont

Can you confirm that this is mating? These spotted Gastropteron chacmol were found on sand during the day. These were found with the larger black forms [message #14648 ], and smaller solid purple ones with a yellow border. They swam actively when disturbed. I found hundreds on the sand that afternoon.

Location: Sand Dollar Beach, Stocking Island, Exumas, Bahamas. Size: Approximately 5 mm each (see photograph on ruler. Depth: 3-6 feet of water. January 9, 2005

Anne DuPont
Delray Beach, FL

DuPont, A., 2005 (Aug 30) Gastropteron chacmol mating?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Anne,
Thanks for these interesting photos. I have combined two [lower left] into a composite soI could display them together. It is nice to see the inside of the parapodia. It almost looks as though the dark red spots are on the inside surface. As to mating, I'm not sure. I have seen species of Siphopteron mating and they are like aglajids mating 'head to tail'. In cephalaspids the penis is on the right side of the head while the female opening is on the right side nearer the tail than the head so usually they don't mate right side to right side as in nudibranchs, because the parapodia are in the way. I also remember Bob Burn suggesting many years ago that in a species he looked at, the flagellum seemed to be involved in mating behaviour. My feeling is that this could be described as 'dating' rather than 'mating' but we still have a lot to learn about their biology.
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Aug 30). Comment on Gastropteron chacmol mating? by Anne DuPont. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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