Re: Glaucus in New Zealand

February 26, 1999
From: Ross Armstrong

Hi Bill
I read their letter again when I got home and it was me who got the id wrong. They had correctly identified it as Glaucus atlanticus and I had made the mistake in my earlier email. They had also done quite a bit of homework. The first one they found they kept with some Velella to use as food. Unfortunately the Velella died over night as did the Glaucus. They went searching after the next lot of easterlies and found some washed up. First they found some small round jellyfish ranging in size from a pin head to about 10mm across. The closest id they could get was Chondrophore. They found these jellyfish were the preferred food source for the Glaucus they kept. Another comment was that when the feed the Glaucus on a daily basis the mortality rate would climb and concluded that their feeding pattern is on a hit and miss basis.
Here is what they say about them feeding:
"Over the past four days we have watched them feeding. When they come in contact with the food source they wrap themsevles around it sideways and guide the food forward with their fronds (cerata) until they can clasp it with their front fronds. The will either pull the food over their head to eat, or will hang vertically under it while eating. The mouth, which is oval, is located at the front of the head and perhaps is similar to that of a lamprey and the creature will feed voraciously, as though this is this meal is the last it may have for sometime."

Other observations:
"We are unable to detect an anal duct. We think the slight protrusion on the left hand side may house both the anal duct and the reproductive organs as some of the creatures have an opaque white corkscrew like thing protruding from their and yesterday (19 Feb) we noted that two of the creatured seemed to be mating in a back to back position."
"We also noted that when placed in direct sunlight they turn upside down and then back again. Perhaps they are cooling themselves down as their backs are out of the water when they float about. In the sea the wave movement would possibly wash over them thus keeping them cool."
"We also tried using an aquarium pump to keep the water aerated, but this only caused more of them to die. Over-feeding them was also a headache as the death rate started to climb. We think this was due to the toxic nature of the food they ate and figured that they required more time between meals to aid with digestion. We now feed them ever other day."
At one stage they had a total of 38 (the figure of 27 was another mistake I made). Unfortunately a lot had died and they decided to release them:
"The decision has been made to release the survivors as we are unable to locate any more food for them. We took the survivors up to the river mouth and released them into the out going current. What we noticed was that when back in their natural habitat they folded their appendages and fronds back towards their body and stayed just under the surface, whereas in captivity they floated high in the water with their appendages and fronds extended outwards."
Another interesting comment:
"We noted that the waste produced by the Glaucus formed a fine cobweb the occupied the bottom half of the bowl and may be toxic to them. Hence the high death rate when we introduced the air pump."
This may actually be the short egg strings you mentioned.
"We noticed the very small Glaucus (1-2mm long) seemed to disappear overnight when there was a lack of food and also some of the smaller ones starting to loose some of their fronds. We came to the conclusion that Glaucus developed cannibalistic tendencies where there was a food shortage and the larger ones would eat the smaller ones."
Their finishing comment:
"These findings are not based on a scientific study of Glaucus atlanticus but are based on what we noted on a daily basis over the past week."

Personally I think they did an excellent job and I apologise for the inaccuracies of my first e-mail which I wrote without having the letter readily available.

Ross Armstrong

Armstrong, R., 1999 (Feb 26) Re: Glaucus in New Zealand. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Ross,
Thanks for the fuller notes. You are right they have done an excellent job. I wonder whether the small jellyfish is in fact Porpita, the third animal I mentioned. It has a round flattened disc with blue tentacles which stick out all over the bottom of the disc and around the edge. Physalia, Velella and Porpita are all "siphonophores" are group of cnidarians in which each "animal" is better thought of as a colony of polyps, in which the polyps are specialised for particular jobs. In Physalia, for example, one polyps forms the float, others are mouths, others long tentacles, etc.

I wish we could get this sort of information on all nudibranchs.

best wishes,
Bill Rudman.

Rudman, W.B., 1999 (Feb 26). Comment on Re: Glaucus in New Zealand by Ross Armstrong. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Glaucus atlanticus

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