Float like a Butterfly

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Merry

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Location
Torrance, California
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Posted by Merry on December 03, 2012 at 10:09:18:





One of the most enchanting and graceful gelatinous blobs in midwater has to be the sea butterfly, Corolla spectabilis. Members of the subclass Opisthobranchia, they’re planktonic members of the wide, wide world of sea slugs.

Because sea butterflies belong to a family of animals that are descendents of gastropods, portions of the molluscan foot have been modified to form swimming wings. Corolla is generally a passive drifter. However, at any disturbance, it vigorously flaps its oval wingplate, propelling itself past surprised divers with remarkable speed. Nearly transparent with a swimming rate of eighteen inches per second, a fleeting glimpse is often all one gets.






Illustration taken from John A. McGowan The Veliger, Vol. 3, May 1, 1968.





Planktonic survival depends on maintaining buoyancy, and expending as little energy as possible to offset sinking. Consequently, the fragile sea butterfly has no shell. Its internal organs are supported by a gelatinous pseudoconch, which is neutrally buoyant.

Perhaps tubercles serve to increase surface area, which would further reduce the sinking rate.





The darkly pigmented spots around the periphery of the wing margin are light sensing organs. A strobe flash may send the animal bobbing and weaving.





A fascinating and almost unimaginable feature of the sea butterfly is the unique way in which it captures food. It starts with a row of mucous glands embedded in the wing margin.




In combination with an internal pallial gland, these glands produce sticky mucous which is then formed by the proboscis into a delicate feeding web, which can be many times larger than the animal.




The web traps planktonic particles ranging from bacteria to single cell algae to copepods and other crustaceans. As ciliary pathways convey the web to the mouth, the grooves of the proboscis consolidate the whole enchilada into a string. Sorting occurs, some food and mucus are rejected, and the rest is consumed.

The next time sea butterflies are in town, watch the motionless ones closely, as they most likely have a flat or funnel-shaped web extended.






Corolla spectabilis actually swims backwards, pushing its pseudoconch forward, with the mouth and feeding web bringing up the rear. The proboscis always stays in contact with the web. If disturbed, the animal may shed the web and swim away. Unfortunately, a strobe flash sometimes qualifies as a disturbance!
 
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OMG, Merry, how DO you get these unbelievably detailed shots of tiny, translucent animals which are in constant motion? My hat is so totally off to you . . . not to mention that you have my thanks for the great educational material.
 
I agree, those shots are incredible!
 
Thank you for your kind words, Lynne. Getting those shots doesn't reflect any particular skill on my part, I promise. It's really the camera and lens, combined with a mild obsession for gelatinous invertebrates. I had no idea about the biology of these animals until I downloaded the photos and noticed what looked "schumtz" trailing from them. Then I had to find books that gave more details about the little beasts!
 
Stunning series Merry! Crisp, clean, superbly composed. Doesn't get much better then that. Never would have even guessed that they were mucous netters. I always look forward to your "science" posts. Thank you for taking the time to share your knowledge with us.
 
Amazing! Thank you, Merry.
I had no idea they cast a net for their supper.

We saw many of these in the top 10 feet off Anacapa Island two days ago.
Next time, I'll be looking for the little nets.
Thanks for doing the homework and sharing the info.

~~~~~
Claudette
 
Wonderful stuff, Merry. Love the photos and the information.
 
In Ah...
 
Learn something new everyday!!!

We're due to hit Ship Rock this weekend so hopefully I'd get to see some.
 

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