Questions about Glaucus

April 25, 2002
From: Luke Short

Dear Bill,
I am a lifeguard on the Sunshine Coast and lately we have been experiencing strong onshore winds. With these consistent winds of course, I have noticed many of these organisms being washed onto the beach- more often then not at the same time. Until I discovered this website I had been absolutely puzzled in regard to identifying what these creatures were and I basically knew nothing about them except whether or not they harmful to humans (such as the bluebottle Physalia physalis ). I have noticed that when I pick up a Glaucus or Glaucilla it leaves some blue part of its anatomy on my hand - they appear to be the cerata(?). Do you know why the organism does this? Another question I have regards the Purple Bubble-raft Snail (Janthina janthina ). When I provoked a floating snail, it appeared to emit a bright blue fluid into the water as some kind of defence mechanism. Is it possible for you to shed some light on this matter?

Thankyou for your time and also for such a great website. So many people ask me what these creatures are and up until now I have been substantially clueless!
Thankyou,
Luke.

lukeshort1979@hotmail.com

Short, L., 2002 (Apr 25) Questions about Glaucus. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/6718

Dear Luke,
I have been meaning to put up a page on Bluebottles and Janthina since they are so associated with Glaucus and Glaucilla so your question was a good opportunity.

Firstly on the blue bits that break off Glaucus and Glaucilla. Yes they are cerata. Quite a few nudibranchs break off parts of their bodies as a defensive strategy, a bit like a lizard dropping its tail. Have a look at the Autotomy page. As you've no doubt read, Glaucus and Glaucilla store stinging nematocysts from the Bluebottles in their cnidosacs and firing them is their first line of defence. At times though they will break off a whole ceras.

I haven't seen Janthina spp called 'Purple Bubble-raft Snails' before, but it is an appropriate name. They produce a bubbly mass of mucus - much like a garden snail - which hardens to form a float so they can stay at the water surface where they feed on Bluebottles. The purple ink they produce is produced by a special gland in their mantle called the Hypobranchial Gland. Many marine snails produce such a secretion and one family, the Muricidae, produce a secretion which turns purple or red on exposure to late. Tyrian Purple was a 'red' rather than purple dye, first made in Tyre in the eastern Mediterranean 2-3000 years ago in what was probably one of the earliest chemical industries. The dye was obtained from the hypobranchial gland of muricid snails. It was extremely valuable and in Rome only robes dyed with Tyrian purple were a sign of high office.

This doesn't actually answer your question about its function in Janthina. I'm afraid we have no good idea of the function of the hypobranchial gland and its secretion in any snail. Various functions have been suggested but none have been demonstrated. Another of life's little mysteries.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Apr 25). Comment on Questions about Glaucus by Luke Short. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/6718

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