Glaucus atlanticus
Forster, 1777

Order: NUDIBRANCHIA
Suborder: AEOLIDINA
Family: Glaucidae

DISTRIBUTION

Circumglobal in temperate and tropical waters.

PHOTO

UPPER: Collaroy Beach, Sydney, February 1987. 4cm long alive. Photographed from above to show the modified foot. Note: as these animals float upside down, their foot is always dorsal. LOWER: Feeding on the "Portuguese man-of-war" or "Bluebottle", Physalia.
PHOTOS: Bill Rudman.

RELATED TOPIC

Glaucilla marginata

Glaucus atlanticus and its close relative, Glaucilla marginata, live in close association with what Sir Alistair Hardy described many years ago as "The Blue Fleet" - the siphonophores such as Physalia, Velella, Porpita and the other associated animals including the "Violet snails" of the genus Janthina. All these animals float on the surface of the ocean being carried by the currents and the winds. Most of us are only aware of their existence when days of onshore winds blow great fleets of them on to the beaches, causing pain and angst for swimmers.

Both species spend their life floating upside down in the water, partially bouyed by a gas bubble in their stomachs.

The two nudibranchs feed almost exclusively on Physalia, and as Tom Thompson and Isobel Bennett reported some years ago, it appears that they are able to select the most venomous of Physalia's stinging nematocysts for their own use. Like most aeolids, they store the nematocysts in special sacs (cnidosacs) at the tip of their cerata .

There are a number of reports in Australia of kids engaged in "Bluebottle" fights - where they throw stranded Physalia at each other - being badly stung by inadvertently playing with Glaucus and Glaucilla, both of which, by concentrating the most venomous of Physalia's nematocysts, are much more deadly.

Another interesting feature of the two species is their colouration. They both exhibit a textbook example of colour countershading. Their foot and undersides of the cerata, (which because they float upside down is effectively their dorsal surface), is blue or blue and white which helps to camouflage them from predation (sea birds) from above. Their true dorsal surface, which faces down in the water, is silvery grey to effectively camouflage them from fish looking up from below.

See photos of pelagic egg strings.

References:
• Bergh, L.S.R. (1884) Report on the Nudibranchiata dredged by H.M.S. Challenger during the years 1873-1876. Report of the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873-76, ... Zoology, 10(26): 1-154, pls. 1-14. [Glaucus: p.10-16]
• Forster, G. (1777) A voyage round the world in His Britannic Majesty's sloop, Resolution, commanded by Capt. James Cook, during the years 1772, 3, 4, and 5 by George Forster. Vol 1: p49.
• Thompson, T.E. & McFarlane, I.D., 1967. Observations on a collection of Glaucus from the Gulf of Aden with a critical review of published records of Glaucidae (Gastropoda, Opisthobranchia). Proceedings of of the Linnean Society, 178: 10-123.
• Thompson,TE. & Bennett,I., 1969. Physalia nematocysts: Utilised by mollusks for defense. Science, 166: 1532-1533.
• Thompson,TE. & Bennett,I., 1970. Observations on Australian Glaucidae (Mollusca: Opisthobranchia). Zoological Journal of the Linnean Society, 49: 187-197.

Authorship details
Rudman, W.B., 1998 (November 6) Glaucus atlanticus Forster, 1777. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/glauatla

Related messages

  1. Glaucus from South Africa
    From: Emil H Niksch, May 3, 2010
  2. Glaucus atlanticus from Florida
    From: Stephanie Armentrout, April 30, 2010
  3. Glaucus atlanticus from nthn New South Wales
    From: Jayson Dyer, April 23, 2010
  4. Re: Glaucus atlanticus from Florida
    From: Douglas Hernandez, April 6, 2010
  5. Glaucus atlanticus from Florida
    From: Emma C., April 5, 2010
  6. Blue Bottles and Nudibranch washed up at Kiama, NSW
    From: Cherie Noon, March 24, 2010
  7. Glaucus atlanticus in Hawaii
    From: Aaron Silva, January 29, 2010
  8. Glaucus atlanticus find in Northern NSW Australia
    From: Matthew Ross, January 20, 2010
  9. Glaucus atlanticus from Hawaii
    From: Enjoli' Hoskins, September 8, 2009
  10. Occurrence of albino Glaucus atlanticus?
    From: Evan Orellana, August 31, 2009
  11. Glaucus atlanticus from Pacific coast of Panama
    From: Clark Misner, May 14, 2009
  12. My Glaucus atlanticus Report
    From: Kenneth Hattersley, May 14, 2009
  13. Glaucus atlanticus in Gulf of Mexico?
    From: Kenneth Hattersley, April 7, 2009
  14. Re: Tiny, elaborate creature at Stradbroke Island, Queensland
    From: Paul Stewart, March 17, 2009
  15. Glaucus atlanticus from Kenya
    From: Debs North, January 8, 2009
  16. Tiny, elaborate creature at Stradbroke Island, Queensland
    From: Ken Thomas, December 3, 2007
  17. Glaucus atlanticus from Pacific coast of Mexico
    From: Joe Weiss, March 7, 2007
  18. Sea Lizard [Glaucus atlanticus] from New South Wales
    From: Lynne T., March 2, 2007
  19. Glaucus atlanticus mating habits
    From: Johanna Schwartz, January 29, 2007
  20. Glaucus atlanticus in Hawaii
    From: Nichol Miura, January 16, 2007
  21. What type of Nudibranch is this?
    From: Adrian Giles, January 15, 2007
  22. Re: Glaucus atlanticus on Gold Coast, Queensland
    From: Rob Alesbury, January 15, 2007
  23. Glaucus atlanticus on Gold Coast, Queensland
    From: John Campbell, December 14, 2006
  24. Glaucus eating Porpita in Hawaii
    From: Anna-Christina Amason, August 17, 2006
  25. Feeding and some trophic interactions of Glaucus atlanticus
    From: Irina Roginskaya, August 2, 2006
  26. About egg masses of Glaucus atlanticus
    From: Irina Roginskaya, May 25, 2006
  27. Unknown creature from Fraser Island, Queensland
    From: Richard Wilsher, May 9, 2006
  28. Some notes about Glaucus atlanticus
    From: Irina Roginskaya, May 9, 2006
  29. Not sure if this IS a sea slug?
    From: Mary Patterson, April 26, 2006
  30. Glaucus at Anna Bay, New South Wales
    From: Jim Doyle, March 31, 2006
  31. Re: Cannibalism in Glaucus?
    From: Peter Whiter, March 30, 2006
  32. Cannibalism in Glaucus?
    From: Peter Whiter, March 28, 2006
  33. What the ?
    From: Eve Whicker, March 23, 2006
  34. What is Filurus dubius?
    From: Gary Rosenberg, February 24, 2006
  35. Glaucus atlanticus - habitat
    From: Brandon Pinkney, February 21, 2006
  36. Is this a sea slug ??
    From: Karen Beal, February 14, 2006
  37. Blue Sea slug
    From: Liliana Alaniz, February 2, 2006
  38. Glaucus atlanticus from the Canary Islands
    From: Kim Boettcher, May 23, 2005
  39. Information on Glaucus atlanticus
    From: Kealy Baker-Clark, April 22, 2005
  40. Blue, lizard-like feather-finned tiny animal
    From: Paiton Meurer, April 14, 2005
  41. Glaucus atlanticus from Reunion Island
    From: Philibert Bidgrain, February 19, 2005
  42. Found some interesting sea slugs in Florida
    From: Sarah McDowell, January 31, 2005
  43. Neon Blue sea slug from Fraser Island?
    From: Neil Rhodes, January 1, 2005
  44. Is this a nudibranch?
    From: Scott Godwin, January 21, 2004
  45. Glaucus atlanticus from Sth Africa
    From: Juleen du Toit, January 21, 2004
  46. Glaucus atlanticus from Queensland
    From: Nick Falconer , December 3, 2003
  47. Glaucus from Wellington Pt, Brisbane
    From: Mimi & Phong, November 17, 2003
  48. Glaucus in Hawaii
    From: Chaunte Ling, May 27, 2003
  49. Mysterious blue and white swirley things
    From: Sally, April 25, 2003
  50. Re: Glaucus in Sydney
    From: Alex & Marcus Dawes, March 19, 2003
  51. Glaucus in Sydney
    From: Alex and Marcus Dawes , March 12, 2003
  52. Glaucus atlanticus from Lord Howe Island
    From: W.B. Rudman, January 24, 2003
  53. Glaucus atlanticus reference
    From: Michael Schroedl, November 14, 2002
  54. Glaucus atlanticus - observations
    From: A. Lovatt., October 21, 2002
  55. Thanks
    From: Amanda Johnson, June 15, 2002
  56. Glaucus atlanticus information
    From: Manda, June 6, 2002
  57. Re: Collaroy 'Blue Dragon' - thanks
    From: Stephen Martin, May 23, 2002
  58. Mass of blue dragon(?) nudibranchs
    From: Stephen Martin, May 20, 2002
  59. Questions about Glaucus
    From: Luke Short, April 25, 2002
  60. Blue plankton in Uruguay
    From: Philip Miller, February 16, 2002
  61. Glaucus from Pensacola, Florida
    From: Elvira Davis, February 4, 2002
  62. Re: Glaucus detecting prey
    From: Belinda Biggam, March 18, 2001
  63. Glaucus detecting prey
    From: Belinda Biggam, March 15, 2001
  64. Re: Glaucus
    From: Lisa, February 20, 2001
  65. Glaucus
    From: Chris Parks, August 24, 2000
  66. Information on Glaucus atlanticus
    From: Angela, August 12, 1999
  67. Eggs of Glaucus and Glaucilla
    From: Bill Rudman, May 16, 1999
  68. Glaucus & Porpita in New Zealand
    From: Ross Armstrong, March 31, 1999
  69. Re: Glaucus in New Zealand
    From: Ross Armstrong, February 26, 1999
  70. Glaucus in New Zealand
    From: Ross Armstrong, February 25, 1999

Show factsheet and all related messages