Re: Gelatinous organism from Alaska

July 4, 2000
From: Jeff Goddard

Hi Bill,

Regarding George Benson's message of July 1. From his description I'd guess they found either a heteropod prosobranch or a pseudothecosome pteropod opisthobranch, Corolla spectabilis. Both are pelagic, gelatinous, and good swimmers. The heteropods have a single ventral swimming fin, while the Corolla have 2 large swimming "wings". Both appendages are modified feet. Corolla has a gelatinous pseudoshell which when washed ashore looks like a rounded glass slipper with small warts on it. Some but not all heteropods (when intact) have a small rudimentary shell that covers only the viscera.

George: have a look at Pacific Coast pelagic Invertebrates by David Wrobel and Claudia Mills (Sea Challengers, 1998); it has great photos and natural history info on these organisms (but incorrectly identifies C. spectabilis as C. calceola).

PS: The other gelatinous planktonic organisms with fin like extensions of the body are the gymnosome pteropod opisthobranchs ("sea butterflies") and chaetognaths (arrow worms).

Best wishes,

Goddard, J., 2000 (Jul 4) Re: Gelatinous organism from Alaska. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jeff,
Thanks for your thoughts on the George's gelatinous mystery from Alaska. It's always a bit difficult when you have no picture. I wondered if the animal was a pteropod. My understanding of its shape from George's message was that the wings were like the wings (cerata) of Melibe rather than the oral hood. My impression of Corolla is that it has a large bilobed wingplate (up to 50mm across) which rather dominates the rest of the body. I have added a rough sketch alongside.

My feeling is that if George's animal is a sea slug then it may possibly be a gymnosome.
I have added a page on the gymnosome Cliopsis krohni, not because I think it is the one George saw but simply because it is the only one I have a photo of. By coincidence I note that this species feeds exclusively on Corolla!

George, have a look at the pictures of these two animals and let us know if they bear any resemblance to what you saw. Pteropods are a fascinating collection of pelagic sea slugs which spend their whole life swimming and floating in the sea. The usually smaller thecosomes, have a lightly calcified shell and feed on smaller plankton, and the usually larger gymnosomes feed on the thecosomes. I have added a photo of one type of thecosome, Creseis acicula, but there are many different species with quite differenty shaped shells, including some with more typical spiral shells.

Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Jul 4). Comment on Re: Gelatinous organism from Alaska by Jeff Goddard. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from



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