Glaucilla marginata from sthn Queensland

February 13, 2009
From: Gary Cobb

Concerning message #22156:

Hi Bill and everyone!
This time the topic is Glaucilla marginata. There are not very many entries for this little beauty, so here we go.

This species is quite common along the beaches after a big onshore wind. They are typically quite small compared to Glaucus atlanticus. I have included a great frontal shot clearly showing the multi-layered cerata [upper photo]; a photo comparing size of large G. atlanticus and small G. marginata [middle photo]; and a mating pair [lower photo]. During the mating I was quite amazed at the actual size on the sexual organ. Nearly the length of the 'arm'. My guess is that with a short organ would not reach because of the size of the 'arm'.

Locality: Mooloolaba, Sunshine Coast, stranded on beach, Queensland, Australia, Pacific Ocean, 20 January 2009, Pelagic. Length: 5-17 mm. Photographer: Gary Cobb.


Cobb, G.C., 2009 (Feb 13) Glaucilla marginata from sthn Queensland. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Gary,

Thanks for this great set of photos. Glaucilla marginata is often overlooked when found with the much larger Glaucus atlanticus. Both species have extremely large copulatory organs and your suggestion that it is because they can't get close together is eminently reasonable. I think Charles Darwin - whose 200th birthday we are celebrating at present - was the first to note the extremely long penis of the humble barnacle - proportionally the longest in the animal kingdom - an adaptation for an animal permanently stuck on a rock. A long penis is their way of getting 'close together'.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Feb 13). Comment on Glaucilla marginata from sthn Queensland by Gary Cobb. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Related messages

  1. Re: Tiny, elaborate creature at Stradbroke Island, Queenslan
    From: Rob Blackmore, January 20, 2009
  2. Re: Nematocysts in Glaucilla
    From: Julia Busch, January 21, 2001
  3. Nematocysts in Glaucilla
    From: Julia Busch, January 20, 2001
  4. Glaucilla marginata - any east Pacific records?
    From: Orso Angulo, January 29, 2000

Show factsheet and all related messages